Background

(1,3)-β-Glucan callose is a cell wall polymer that is involved in several fundamental biological processes, ranging from plant development to the response to abiotic and biotic stresses. Despite its importance in maintaining plant integrity and plant defence, knowledge about the regulation of callose biosynthesis at its diverse sites of action within the plant is still limited. The moderately sized family of GSL (GLUCAN SYNTHASE-LIKE) genes is predicted to encode callose synthases with a specific biological function and subcellular localization. Phosphorylation and directed translocation of callose synthases seem to be key post-translational mechanisms of enzymatic regulation, whereas transcriptional control of GSL genes might only have a minor function in response to biotic or abiotic stresses.

Scope and Conclusions

Among the different sites of callose biosynthesis within the plant, particular attention has been focused on the formation of callose in response to pathogen attack. Here, callose is deposited between the plasma membrane and the cell wall to act as a physical barrier to stop or slow invading pathogens. Arabidopsis (Arabidopsis thaliana) is one of the best-studied models not only for general plant defence responses but also for the regulation of pathogen-induced callose biosynthesis. Callose synthase GSL5 (GLUCAN SYNTHASE–LIKE5) has been shown to be responsible for stress-induced callose deposition. Within the last decade of research into stress-induced callose, growing evidence has been found that the timing of callose deposition in the multilayered system of plant defence responses could be the key parameter for optimal effectiveness. This timing seems to be achieved through co-ordinated transport and formation of the callose synthase complex.

INTRODUCTION

Callose is a (1,3)-β-glucan cell wall polymer with some (1,6)-branches (Aspinall and Kessler, 1957). It is found in all multicellular green algae as well as higher plants (Scherp et al., 2001). The amount and distribution of callose are highly variable depending on developmental stages and the presence of biotic as well as abiotic stresses.

During cytokinesis callose is transiently deposited in the cell plate of the phragmoblast. It has also been also associated with pollen self-incompatibility (Dumas and Knox, 1983) and pollen development (McCormick, 1993; Fei et al., 2004). Callose is also an essential component of the transient cell wall surrounding pollen mother cells and encloses the four microspores after meiosis. In addition, callose forms a pre-cell wall at the growing pollen tube tip (Edlund et al., 2004). Sieve plates, which are a basic component of the phloem, are already rich in callose under normal growing and developmental conditions (Hartig, 1851; Eschrich, 1956). When subjected to stress, callose accumulates rapidly and plugs the sieve pores. Similar to this stress response, callose biosynthesis and degradation in the neck region of plasmodesmata help to regulate permeability during abiotic and biotic stresses. In response to pathogen attack, callose is deposited between the plasma membrane and the pre-existing cell wall at sites of pathogen attack (Nishimura et al., 2003).

Even though callose is involved in multiple, important biological processes in the plant, detailed knowledge about the regulation of this cell wall polymer and its specific function has not been provided for all diverse callose synthase family members. Major contributions to elucidate the biosynthesis and regulation of callose deposition were made by Hong et al. in 2001 and by Jacobs et al. and Nishimura et al. in 2003. They provided for the first time a detailed insight into the biological role of two callose synthase family members.

Apart from solving questions about stress-induced callose biosynthesis in general, the findings of Jacobs et al. (2003) and Nishimura et al. (2003) also raised new questions about the effectiveness and importance of pathogen-induced callose deposition at sites of infection. Because they showed enhanced pathogen resistance for arabidopsis mutants that were deficient in stress-induced callose deposition, callose was regarded as a possible by-product of the response to pathogen attack, without an important biological role in plant defence. Its ongoing utilization as marker for general alterations in pathogen defence responses or to screen new elicitors (McCann et al., 2012) was not affected. This kind of usage benefited from the easy staining of this cell wall polymer with the fluorophore aniline blue (Currier, 1957) in histological examination with an epifluorescence microscope with a UV filter, either with (Luna et al., 2011) or without destaining of the plant tissue and in combination with fluorescent proteins or fluorescent dyes that are specific for distinct organelles or cellular structures (Xie et al., 2012). Within recent years, several methods have been published that describe different approaches to the quantification of time-dependent callose formation to investigate the regulation of callose biosynthesis. They range from measuring callose intensity by counting white pixels of digital photographs or by calculating the number of depositions relative to the total number of pixels using office solutions like Photoshop (Luna et al., 2011) or scientific software like ImageJ (Li et al., 2009) to the application of automated analysis using the Acapella framework (Zhou et al., 2012). The first successful application of super-resolution microscopy to aniline blue-stained callose deposits after fungal infection, which allows visualization of nanoscale, 3-D polymer networks (Eggert et al., 2014), opens new possibilities in the histological examination of stress-induced structural modification of callose and its interaction with other cell wall polymers.

This article summarizes what is known about the regulation of callose synthase activity as well as what has been discussed with regard to this topic within the last decade based on results derived from new techniques and available mutant lines. We focus especially on the progress that has been made in understanding the regulation of callose biosynthesis in response to pathogen attack.

OVERVIEW OF THE ARABIDOPSIS CALLOSE SYNTHASE FAMILY

In most plants, the group of callose synthases encoding GSL (GLUCAN SYNTHASE-LIKE) genes forms a moderately sized gene family. The predicted function of GSL-encoded proteins as callose synthases is based on their homology with the yeast (Saccharomyces cerevisiae) FKS (FK506 SENSITIVITY) genes, which encode subunits of predicted (1,3)-β-glucan synthase complexes (Douglas et al., 1994; Dijkgraaf et al., 2002). In the best-studied model plant, arabidopsis (Arabidopsis thaliana), 12 GSL genes have been identified, which were initially designated as GSL1–GSL12 (Richmond and Somerville, 2000). A parallel annotation referred to these genes as callose synthase genes CalS1CalS12 (Verma and Hong, 2001). The numerical designation has not been aligned in these two annotation approaches, which might result in confusion. Although a callose synthase function is very likely for most members of this gene family, direct biochemical evidence for callose synthase activity has not been provided yet, which prompted us to continue using the conservative GSL nomenclature. A comparative list of the parallel annotations is provided in Table 1 together with additional information on their individual biological roles (as far as known).

Table 1.

Overview of subcellular localization and biological role of callose synthases encoded by the GSL gene family in Arabidopsis

GSL1 CalS2 Gene ID3 Subcellular localization (experimental) Biological function 
Biological role in fertility and cell division 
GSL1 CalS11 AT4G04970 MS/MS: plasma membrane (Benschop et al., 2007Pollen development and fertility (Enns et al., 2005
GSL2 CalS5 AT2G13680 GFP-tagged protein in cultured tobacco BY-2 cells: plasma membrane and Golgi-related endo-membranes (Xie et al., 2012Found in mature pollen grains (Grobei et al., 2009); involved in late stages of pollen development and pollen tube (Dong et al., 2005; Xie et al., 2010
GSL6 CalS1 AT1G05570 GFP-tagged protein: cytosol and plasma membrane (Hong et al., 2001a); MS/MS: plasma (Alexandersson et al., 2004; Keinath et al., 2010; Benschop et al., 2007; Zhang and Peck, 2011Required for callose depositions during cell plate formation (Hong et al., 2001a, b
GSL8 CalS10 AT2G36850 MS/MS: plasma membrane (Alexandersson et al., 2004; Mitra et al., 2009; Benschop et al., 2007; Marmagne et al., 2007; Zhang and Peck, 2011Required for male gametophyte development and plant growth (Töller et al., 2008); entry of microspores into mitosis (Chen et al., 2009; De Storme et al., 2013); required for callose biosynthesis at the cell plate (Thiele et al., 2009), involved in stomatal pattering and deposition at the plasmodesmata (Guseman et al., 2010; Han et al., 2014
GSL10 CalS9 AT3G07160 MS/MS: plasma membrane (Alexandersson et al., 2004; Dunkley et al., 2006; Benschop et al., 2007; Marmagne et al., 2007; Mitra et al., 2009; Keinath et al., 2010; Zhang and Peck, 2011Required for male gametophyte development and plant growth (Töller et al., 2008); together with GSL8, involved in entry of microspores into mitosis (De Storme et al., 2013
Structural reinforcement 
GSL5 (PMR4) CalS12 AT4G03550 GFP-tagged protein: plasma membrane (Drakakaki et al., 2012; Ellinger et al., 2013); MS/MS: plasma membrane (Alexandersson et al., 2004; Dunkley et al., 2006; Benschop et al., 2007; Mitra et al., 2009; Keinath et al., 2010; Zhang and Peck, 2011Required for wound and papillary callose formation in response to fungal pathogens (Jacobs et al., 2003; Nishimura et al., 2003; Ellinger et al., 2013; Naumann et al., 2013); important for exine formation and pollen wall patterning (Enns et al., 2005
GSL7 CalS7 AT1G06490 No experimental data Responsible for callose deposition in the phloem (Barratt et al., 2011; Xie et al., 2011
GSL12 CalS3 AT5G13000 MS/MS: plasma membrane (Benschop et al., 2007; Keinath et al., 2010; Zhang and Peck, 2011Required for callose deposition at plasmodesmata (Sevilem et al., 2013
Unknown function     
GSL3 CalS2 AT2G31960 MS/MS: plasma membrane (Alexandersson et al., 2004; Benschop et al., 2007; Kierszniowska et al., 2009Unknown function 
GSL4 CalS8 AT3G14570 No experimental data Unknown function, found in roots (Lan et al., 2011
GSL9 CalS4 AT5G36870 No experimental data Unknown function, found in leaf membranes (Mitra et al., 2007
GSL11 CalS6 AT3G59100 No experimental data Unknown function 
GSL1 CalS2 Gene ID3 Subcellular localization (experimental) Biological function 
GSL1 CalS2 Gene ID3 Subcellular localization (experimental) Biological function 
Biological role in fertility and cell division 
GSL1 CalS11 AT4G04970 MS/MS: plasma membrane (Benschop et al., 2007Pollen development and fertility (Enns et al., 2005
GSL2 CalS5 AT2G13680 GFP-tagged protein in cultured tobacco BY-2 cells: plasma membrane and Golgi-related endo-membranes (Xie et al., 2012Found in mature pollen grains (Grobei et al., 2009); involved in late stages of pollen development and pollen tube (Dong et al., 2005; Xie et al., 2010
GSL6 CalS1 AT1G05570 GFP-tagged protein: cytosol and plasma membrane (Hong et al., 2001a); MS/MS: plasma (Alexandersson et al., 2004; Keinath et al., 2010; Benschop et al., 2007; Zhang and Peck, 2011Required for callose depositions during cell plate formation (Hong et al., 2001a, b
GSL8 CalS10 AT2G36850 MS/MS: plasma membrane (Alexandersson et al., 2004; Mitra et al., 2009; Benschop et al., 2007; Marmagne et al., 2007; Zhang and Peck, 2011Required for male gametophyte development and plant growth (Töller et al., 2008); entry of microspores into mitosis (Chen et al., 2009; De Storme et al., 2013); required for callose biosynthesis at the cell plate (Thiele et al., 2009), involved in stomatal pattering and deposition at the plasmodesmata (Guseman et al., 2010; Han et al., 2014
GSL10 CalS9 AT3G07160 MS/MS: plasma membrane (Alexandersson et al., 2004; Dunkley et al., 2006; Benschop et al., 2007; Marmagne et al., 2007; Mitra et al., 2009; Keinath et al., 2010; Zhang and Peck, 2011Required for male gametophyte development and plant growth (Töller et al., 2008); together with GSL8, involved in entry of microspores into mitosis (De Storme et al., 2013
Structural reinforcement 
GSL5 (PMR4) CalS12 AT4G03550 GFP-tagged protein: plasma membrane (Drakakaki et al., 2012; Ellinger et al., 2013); MS/MS: plasma membrane (Alexandersson et al., 2004; Dunkley et al., 2006; Benschop et al., 2007; Mitra et al., 2009; Keinath et al., 2010; Zhang and Peck, 2011Required for wound and papillary callose formation in response to fungal pathogens (Jacobs et al., 2003; Nishimura et al., 2003; Ellinger et al., 2013; Naumann et al., 2013); important for exine formation and pollen wall patterning (Enns et al., 2005
GSL7 CalS7 AT1G06490 No experimental data Responsible for callose deposition in the phloem (Barratt et al., 2011; Xie et al., 2011
GSL12 CalS3 AT5G13000 MS/MS: plasma membrane (Benschop et al., 2007; Keinath et al., 2010; Zhang and Peck, 2011Required for callose deposition at plasmodesmata (Sevilem et al., 2013
Unknown function     
GSL3 CalS2 AT2G31960 MS/MS: plasma membrane (Alexandersson et al., 2004; Benschop et al., 2007; Kierszniowska et al., 2009Unknown function 
GSL4 CalS8 AT3G14570 No experimental data Unknown function, found in roots (Lan et al., 2011
GSL9 CalS4 AT5G36870 No experimental data Unknown function, found in leaf membranes (Mitra et al., 2007
GSL11 CalS6 AT3G59100 No experimental data Unknown function 
GSL1 CalS2 Gene ID3 Subcellular localization (experimental) Biological function 
1

Annotation according to Richmond and Somerville (2000).

2

Annotation according to Verma and Hong (2001).

3

Gene identifier according to The Arabidopsis Information Source (http://www.arabidopsis.org).

Subcellular localization of callose synthases

A minimum of ten transmembrane domains were predicted for all 12 members of the arabidopsis callose synthase family using the ARAMEMNON database (Schwacke et al., 2003) and the TMHMM Server v. 2.0 (http://www.cbs.dtu.dk/services/TMHMM), which would imply a membrane localization and has already been confirmed for eight callose synthases. Most experimental data have been derived from membrane preparations followed by mass spectrometry analysis (Table 1). In addition to a general localization in membranes, callose synthases might accumulate in detergent-resistant membrane fractions, the so-called lipid rafts, as recently shown for callose synthases from cultured poplar (Populus trichocarpa) cells (Srivastava et al., 2013). However, accumulation of callose synthases in lipid rafts could be plant-specific, because unequal distribution could not be detected in arabidopsis using either cell-fractioning experiments or callose synthases tagged with fluorescent proteins. In this regard, the arabidopsis callose synthases GSL2, GSL5 and GSL6 were successfully fused with a fluorescent protein. The green fluorescent protein (GFP)-tagged GSL2 and GSL5 co-localized with FM4-64, a lipophilic fluorescent dye and plasma membrane marker (Bolte et al., 2004), without showing preferences for putative membrane regions. In addition, GSL2 (Xie et al., 2012) and GSL5 (Drakakaki et al., 2012; Ellinger et al., 2013) were also found in vesicle-like structures, which indicates a possible transport mechanism for callose synthases to sites of required callose biosynthesis, raising questions about putative regulatory pathways involved in targeted translocation.

Biological role of callose synthase family members in pollen fertility and plant development

A reason for the limited knowledge of the biological role of specific callose synthases can be found in the lack of phenotypes for specific gsl disruption mutants, which could indicate partially redundant functions. Especially in plant growth and development, experimental data support the assumption of possible redundancy. Callose synthases encoded by GSL1, GSL2, GSL5, GSL8 and GSL10 were required for callose biosynthesis during pollen development and were essential for pollen fertility and/or viability. GSL1 and GSL5 were required for the formation of the callosic cell wall that separates the microspore in the tetrad and for subsequent pollen grain maturation (Enns et al., 2005). The degeneration of microspores in gls2 disruption mutants indicated that this callose synthase would be required for exine formation during microgametogenesis (Dong et al., 2005). The disruption mutants gsl8 and gsl10 showed perturbation in the symmetry of microspore division and had irregular callose deposition during microgametogenesis (Töller et al., 2008). In addition, the GSL8- and GSL6-encoded callose synthases play a role in forming premature cell walls at cell plates of dividing cells. Together with GSL12, GSL8 predominantly contributes to callose deposition at plasmodesmata (Guseman et al., 2010; Sevilem et al., 2013). So far, only GSL7 has been shown to be responsible for the synthesis of callose in sieve plate pores (Barratt et al., 2011; Xie et al., 2011).

Biological role of callose synthase family members in stress and pathogen response

Regarding stress-induced callose biosynthesis, GSL5 (in the context of pathogen response first described as PMR4; POWDERY MILDEW RESISTANT4) encodes the callose synthase that is responsible for the deposition of callose in papillae, which are cell wall thickenings at sites of pathogen attack and at wounding sites (Jacobs et al., 2003; Nishimura et al., 2003; Kim et al., 2005). In addition to redundancies in callose biosynthesis in developmental processes, there is growing evidence that, apart from GSL5, at least one additional callose synthase could be involved in callose deposition after treatment with purified elicitors from callose-inducing pathogens. The treatment of arabidopsis leaves with chitosan, which is an elicitor associated with fungal pathogens (El Hadrami et al., 2010), also resulted in callose deposition in GSL5 disruption mutants. Comparison with elicitor-induced callose production in wild-type plants revealed that ∼10 % of the callose produced was derived from callose synthase(s) other than GSL5. In contrast, callose deposition induced by flg22, an elicitor derived from the flagellin of bacterial pathogens (Gomez-Gomez et al., 1999), was entirely dependent on GSL5 activity (Luna et al., 2011). Although a redundant callose synthase for pathogen- or elicitor-induced callose formation has not been identified, induction of gene expression was observed for GSL5 and also for GSL6 and GSL11 after biotic stress (Jacobs et al., 2003).

Based on their biological roles, the GSL callose synthase family can be divided into two separate groups. The larger one, including GSL1, GSL2, GSL6, GSL8 and GSL10, is mainly involved in callose biosynthesis during pollen development and cell division. Members of the smaller group, including GSL5, GSL7 and GSL12, are required when callose acts in plugging, barrier formation or other kinds of structural reinforcement. The function of the remaining members, GSL3, GSL4, GSL9 and GSL11, is still unknown. Involvement in a precise biological process and their localization have not been determined yet.

REGULATION OF CALLOSE BIOSYNTHESIS

A common characteristic of the majority of the described callose synthases is their strict temporal and spatial regulation, which is required so that they can fulfil a specific biological function. This leads directly to the question of the regulatory mechanisms that control callose biosynthesis.

Regulation at transcriptional level

Overlapping expression patterns of several GSL genes were observed in response to wounding and physiological stresses as well as in different tissues during plant development (Dong et al., 2008). However, in almost all of these cases of possible transcriptional regulation of GSL genes, alterations of gene expression were relatively moderate and did not exceed a 2·5-fold induction compared with controls, based on our analysis of publicly available expression data provided in the Genevestigator database (Hruz et al., 2008). Exceptions to these moderate inductions were treatments with cycloheximide, which is an inhibitor of protein biosynthesis (Ellis and Macdonald, 1970), and salicylic acid, a phenolic compound that is important for the regulation of multiple physiological processes and plant defence (An and Mou, 2011). Cycloheximide induced up to 50-fold upregulation of GSL3 expression and salicylic acid treatment induced strong GSL5 and GSL6 expression (Dong et al., 2008) regulated by the salicylic acid receptor NPR1 (NON-EXPRESSOR OF PATHOGENISIS-RELATED GENES 1) (Wu et al., 2012). A significant increase in GSL6 expression was also observed after infection with different bacterial Pseudomonas syringae pathovars and the downy mildew Hyaloperonospora arabidopsidis. Based on these expression results, regulation of callose biosynthesis at the transcriptional level seems to be restricted to specific stress situations. However, a transcription factor for the regulation of GSL gene expression in the biotic or abiotic stress response is not known yet. An exception is auxin-induced, callose-mediated plasmodesmatal gating, in which GSL8 expression is regulated by the auxin response factor ARF7 (Han et al., 2014). Another auxin response factor, ARF17, was recently shown to regulate the expression of GSL2 during pollen wall pattern formation (Yang et al., 2013). In addition to ARF17, GSL2 expression seemed to be regulated by pre-mRNA splicing through CYCLIN-DEPENDENT KINASE G1 (CDKG1) during pollen wall formation (Huang et al., 2013). Because the expression of GSL2 was down-regulated in both cdkg1 and arf17 disruption mutants, transcriptional regulation of callose biosynthesis seems to be important during pollen wall pattern formation.

Regulation by phosphorylation

A post-translational modification that has been discussed as a putative mechanism of regulating callose biosynthesis is phosphorylation. In yeast, the activity of the callose synthase homologues FKS1 and FKS2 was dependent on their phosphorylation status (Qadota et al., 1996; Calonge et al., 2003; Ishiguro et al., 2013). Regulation through phosphorylation was also proposed for the arabidopsis callose synthases GSL10, where phosphorylated peptides were identified by mass spectrometry after treatment with elicitor flg22 and xylanase (Benschop et al., 2007), and GSL12 (Nuhse et al., 2003). A GSL5 peptide was found in six independent experimental approaches with phosphorylation at the same serine residue after various stress situations (Nuhse et al., 2007; Sugiyama et al., 2008; Reiland et al., 2009, 2011; Kline et al., 2010; Nakagami et al., 2010). However, a kinase or phosphatase that would regulate the phosphorylation status of a callose synthase in response to stress or at a specific developmental stage has not been identified yet.

Regulation by complex formation

Regulating substrate uptake into the catalytic centre, either by conformational changes or substrate delivery, is another common mechanism of the regulation of enzyme activity. This type of regulation usually depends on accessory proteins interacting with the callose synthase. The formation of high molecular callose synthase complexes with accessory, putative regulatory proteins was first predicted from experiments with yeast (Qadota et al., 1996) and green algae (Stone, 2006). In plants, the arabidopsis callose synthase GSL6 was partially purified with two cell plate-associated proteins, phragmoplastin and the UDP-glucose transferase UGT1 (Hong et al., 2001b). UGT1 also interacted with Rop1, a Rho-like GTPase. Interestingly, this interaction occurred only in the GTP-bound configuration of Rop1, which suggests that the plant callose synthase might be regulated by Rop1 by interaction with UGT1 (Hong et al., 2001b). A monomeric GTPase from the Rho family was also involved in callose biosynthesis in yeast (Calonge et al., 2003). Finally, an annexin-like protein modulated callose synthase activity in cotton (Gossypium hirsutum) (Andrawis et al., 1993). In summary, the hypothetical callose synthase complex proposed by Verma and Hong in 2001, in which the hydrophilic loop may interact with a monomeric GTPase, UGT, annexin and a sucrose synthase, is still a widely accepted model.

Regulation by transport

Phosphorylation and interaction with other proteins might also be involved in the transport and focal accumulation of callose synthases at the various sites of callose biosynthesis. It is known that these regulatory processes are required for the correct timing and amount of callose deposition. Verma and Hong (2001) proposed that Rho-like GTPase might not only regulate callose synthase activity but also function as a spatial regulator. Another well-documented example of a transport process is the production of callose at the growing tip of pollen tubes. Transport of callose synthases in tobacco pollen tubes seemed to start at the endoplasmic reticulum, where the enzyme might be synthesized or processed. Subsequently, they were proposed to be integrated into Golgi bodies and transported along bundles of actin filaments to the subapex of the pollen tube (Cai et al., 2011). These finding were based on the inhibition of vesicle transport. Most knowledge about the transport of callose synthases and the underlying regulatory mechanisms applies to callose biosynthesis at the tips of growing pollen tubes and the stress-induced callose synthase GSL5 from arabidopsis, for which the current discussion about the regulation of plant defence responses is summarized in the following section.

CURRENT VIEWS REGARDING INDUCTION AND REGULATION OF GSL5 IN PLANT–PATHOGEN INTERACTION

Callose biosynthesis in response to plant–bacteria interaction

Apart from abiotic stress and wounding (Wheeler, 1974; Ryals et al., 1996; Jacobs et al., 2003; Mauch-Mani and Mauch, 2005), a wide range of bacteria induce callose deposition in leaf epidermal cells. Based on studies with bacterial elicitors, several pathways were identified that induced callose biosynthesis and depended either on the production of reactive oxygen species (Luna et al., 2011) and salicylic acid (Nishimura et al., 2003; Flors et al., 2008) or the accumulation of indole glucosinolates (Geng et al., 2012). However, precise analysis of the role of GSL5 in basal resistance or innate immunity to bacterial pathogens is generally restricted by the fact that GSL5 disruption mutants revealed a hyperinduction of salicylic acid biosynthesis as well as constitutive expression of plant defence-related genes (Nishimura et al., 2003). In addition, neither the lack of callose deposition nor enhanced callose deposition alone was sufficient to increase resistance to bacterial pathogens (Moreau et al., 2012). Therefore, the biological role of callose in plant–bacteria interaction is still a controversial issue in current discussions. Besides functioning as a physical barrier to prevent ingress of pathogens (Ellinger et al., 2013), callose might form a diffusion barrier (Aist, 1976; Samardakiewicz et al., 2012) or could be involved in the detoxification of antimicrobial compounds (Luna et al., 2011).

Although accumulation of callose in response to pathogen-associated molecular pattern (PAMP) recognition might not primarily contribute to pathogen resistance, this plant defence response can be used to study the regulation and transport of callose synthases. The fast response of a plant to pathogen attack relies on its innate immunity (Jones and Dangl, 2006), which can be divided into two arms: (1) PAMP-triggered immunity (PTI) (Boller and Felix, 2009); and (2) effector-triggered immunity (Senthil-Kumar and Mysore, 2013). PAMPs – or, more generally, MAMPs (microbial associated molecular patterns) – are highly conserved molecular elicitors derived from microbial pathogens. The most prominent bacterial MAMPs, flg22 (Gomez-Gomez et al., 1999; Luna et al., 2011), the elongation factor Tu (EF-Tu) (Lu et al., 2009), lipopolysaccharides (Keshavarzi et al., 2004; Sun et al., 2012) and peptidoglycan hairpins (Erbs et al., 2008; Erbs and Newman, 2012), all elicit callose deposition. MAMPs are recognized by a class of specific plasma-membrane-bound extracellular receptors, the so-called pattern recognition receptors (PRRs) (Dodds and Rathjen, 2010; Beck et al., 2012). MAMP-induced activation of PRRs triggers a series of fast defence responses, which include the production of reactive oxygen species, the induction of mitogen-activated protein kinases (MAPKs) and changes in protein phosphorylation, and were detectable already within the first 5 min after PRR activation. This first wave of responses is followed by ethylene and glucosinolate biosynthesis (Clay et al., 2009), receptor endocytosis (Beck et al., 2012) and induction of gene expression. Callose deposition at infection sites is normally observed within hours after pathogen attack and is therefore classified as a late PTI response. Interestingly, we observed not only callose deposition related to a late PTI response starting 6 h after infiltration of 1 μm flg22 into adult arabidopsis leaves, but also a relatively fast callose response 60–90 min after flg22 treatment (Fig. 1). This early callose response to flg22 treatment is commonly not recorded because in most studies visualization of callose started 18–24 h after treatment. However, also in studies with an early start of flg22-induced callose detection, such as that of Luna et al. (2011), an early callose response was not detected. Differences in the occurrence of an flg22-induced, early callose response could be determined by the method of treatment and the physiological and developmental stage of the plant. Whereas we infiltrated 4-week-old arabidopsis leaves, Luna et al. (2011) added a 1 μm flg22 solution to the growth medium of 9-day-old arabidopsis seedlings.

Fig. 1.

Callose deposition in response to flg22 infiltration. For each time-point, three 4-week-old arabidopsis leaves were infiltrated with 1 μm flg22 solution as described in Daudi et al. (2012) and harvested at the indicated time-points after treatment. Chlorophylls were removed with ethanol to eliminate the auto-fluorescence background in callose visualization with the organic fluorophore aniline blue (Stein et al., 2006). Micrographs were taken by confocal laser-scanning microscopy using a 405 nm diode laser for aniline blue excitation. Emission filtering was achieved using a 472- to 490-nm bandpass filter. (A) Number of callose depositions per mm2 counted by CalloseMeasurer (Zhou et al., 2012). Data are means of three independent experiments with n = 4. Error bars indicate standard deviation. (B) Distribution and amount of callose depositions in leaves stained with aniline blue at indicated time-points after flg22 infiltration. Scale bars = 500 μm.

Fig. 1.

Callose deposition in response to flg22 infiltration. For each time-point, three 4-week-old arabidopsis leaves were infiltrated with 1 μm flg22 solution as described in Daudi et al. (2012) and harvested at the indicated time-points after treatment. Chlorophylls were removed with ethanol to eliminate the auto-fluorescence background in callose visualization with the organic fluorophore aniline blue (Stein et al., 2006). Micrographs were taken by confocal laser-scanning microscopy using a 405 nm diode laser for aniline blue excitation. Emission filtering was achieved using a 472- to 490-nm bandpass filter. (A) Number of callose depositions per mm2 counted by CalloseMeasurer (Zhou et al., 2012). Data are means of three independent experiments with n = 4. Error bars indicate standard deviation. (B) Distribution and amount of callose depositions in leaves stained with aniline blue at indicated time-points after flg22 infiltration. Scale bars = 500 μm.

We previously observed the ability for fast callose deposition in response to stress also in arabidopsis lines with GSL5 overexpression. Epidermal leaf cells of the overexpression line strongly deposited callose 60 min after spraying flg22, in contrast to wild-type and pmr4 lines without an early callose response (Ellinger et al., 2013). These results clearly indicate that initial callose biosynthesis is GSL5-dependent, can be explained by the presence of this enzyme at plasma membrane before treatment, and occurs without de novo protein biosynthesis. We hypothesize that callose deposits observed 6 h after flg22 treatment and later might be mainly derived from transported GSL5 because we did not detect induction of GSL5 expression at this time-point (data not shown). In this regard, Wang and Forbert (2013) also did not find a correlation between callose deposition and GSL5 expression after flg22 infiltration of arabidopsis leaves. Reduction in callose deposition between 120 and 300 min after flg22 spraying may be due to degradation of callose, which we also observed after fungal infections at the first callose deposition (Ellinger et al., 2013).

In addition to studying callose biosynthesis during PTI, analysis of this plant defence response during effector-triggered immunity can provide new insight into the regulation of this process during pathogen attack. As mentioned before, PTI results in callose deposition at the cell wall, but microbial effectors targeting PTI can suppress callose deposition (Hauck et al., 2003; Underwood et al., 2007; Zhang et al., 2007; Fabro et al., 2011). Biotrophic bacterial pathogens have evolved and maintained a type III secretion system to deliver effectors into host cells to suppress elicitor-induced defence responses (Lee et al., 2013). The pathogenic bacterium P. syringae pv. tomato DC3000 secretes the effector proteins Hrp outer protein M1 (HopM1) and coronatine, which structurally mimics active jasmonic acid conjugates. Both effectors target and inhibit distinct signalling steps to suppress callose deposition, which is independent of salicylic acid responses but dependent on the accumulation of indole glucosinolates (Geng et al., 2012). In addition, HopM1 suppresses PTI responses by interfering with vesicle trafficking (Nomura et al., 2011). Pathogen-induced degradation of the trans-Golgi network seems to be critical for invading bacteria to overcome the plant's effector-triggered immunity mechanism for successful colonization. The trans-Golgi network and early endosomes function as a central junction for major endomembrane trafficking events, which are required not only for endocytosis but also for the secretion of apoplastic proteins such as the pathogenesis-related protein PR1 (Wang et al., 2005; Gu and Innes, 2012). Because bacteria-induced callose accumulation was delayed in arabidopsis mutants that were impaired in vesicle-associated secretion processes (Kwon et al., 2008) and their regulation at transcriptional level (Wang and Fobert, 2013), these regulatory mechanisms might also apply to the transport of GSL5, as observed in plant–fungus interaction (Nielsen et al., 2012).

Callose biosynthesis in response to plant–fungus interaction

A further example of highly localized callose accumulation is the deposition of callose in papillae in response to fungal attack at sites of attempted penetration in epidermal cells (Zimmerli et al., 2004; Koh et al., 2005; Nielsen et al., 2012; Ellinger et al., 2013). After powdery mildew infection of arabidopsis leaves, the pathogen-induced callose synthase GSL5 was shown to be recruited from the plasma membrane, where it localized in untreated leaf epidermal cells, to the site of attempted fungal penetration. Here, it was reintegrated into the plasma membrane to generate localized callose plugs (Ellinger et al., 2013). A general transport of callose synthases in the vesicles is also supported by a study by Drakakaki et al. (2012), in which biochemical analysis revealed the presence of GSL5 in the SYP61 trans-Golgi network compartment.

Involvement of transport processes in callose accumulation during papilla formation after fungal attack was also observed by Nielsen et al. (2012). Treatment of leaves with brefeldin A, which is a fungal inhibitor of vesicle transport (Sciaky et al., 1997), inhibited callose accumulation in the papilla. They further proposed that papilla formation would require rapid reorganization of material from the plasma membrane, which might be sorted into multi-vesicular bodies and directed to the site of fungal attack (Nielsen et al., 2012).

Exocytosis mediated by multi-vesicular bodies is well studied in animals (Harding et al., 1983; Pan and Johnstone, 1983). In plants, a retrograde pathway has been proposed that would involve a fusion of multi-vesicular bodies with the plasma membrane, resulting in the delivery of previously intralumenal vesicles to the cell exterior. In barley as well as in arabidopsis, putative multi-vesicular bodies were observed in close contact with the plasma membrane in TEM experiments (An et al., 2006; Micali et al., 2011). However, callose was not detectable in multi-vesicular bodies and vesicles in the central vacuole during microscopy of fixed tissue (An et al., 2006). Further evidence that multi-vesicular bodies play a role in the delivery and assembly of callose and other defence components at the growing papilla was derived from studies with barley in response to the powdery mildew Blumeria graminis f. sp. hordei (Böhlenius et al., 2010). In this pathosystem, a monomeric G-protein from the ADP ribosylation factor (ARF) GTPase (ARFA1b/1c) was associated with plant multi-vesicular bodies and was required for penetration resistance and callose deposition. However, ARFA1b/1c was not required to form the basic structure of papillae. Although ARFA1b/1c mainly localized to Golgi and endocytotic vesicles, it was also identified as a component of multi-vesicular bodies, which might indicate involvement in vesicle budding and callose deposition in papillae. Additional evidence for this hypothesis derived from mutant lines of the ADP ribosylation factor–GTP exchange factor (ARF-GEF) GNOM. The analysis of a partially functional mutant revealed a delay in papilla formation and callose accumulation as well as reduced penetration resistance. Moreover, a time-course study revealed that these gnom mutants had a delay of ∼30 min in the appearance of callose (Nielsen et al., 2012). Combining these results with recent studies of callosic papillae at the site of fungal penetration using super-resolution microscopy (Eggert et al., 2014), it becomes evident that precise timing of pathogen-induced callose biosynthesis is one of the key factors in callose-mediated resistance against biotrophic fungi. The complete penetration resistance of GSL5-overexpressing lines to powdery mildews is based on elevated and massive physical strengthening of the cell wall at infection sites (Ellinger et al., 2013, Naumann et al., 2013), which includes the formation of a physical barrier against pathogen-secreted cell wall hydrolases (Eggert et al., 2014).

CONCLUSIONS AND FUTURE PROSPECTS

Direct evidence for a specific regulatory mechanism of callose biosynthesis in plants has only been provided for pollen wall pattern formation, in which transcriptional regulation of callose formation is very likely. There is also growing evidence for the requirement of transport processes in pathogen-induced callose biosynthesis. Figure 2 summarizes all discussed facts about callose biosynthesis and its regulation in four main spheres of action, which are surrounded by factors that might influence callose regulation related to the specific action, but have not been determined yet. Figure 2 illustrates that profound knowledge already exists, but similar questions are still open within the different spheres of callose action. Also, much basic information, such as direct biochemical proof of the callose synthase activity of all 12 GSL members and the stoichiometry of the active callose synthase complex, is still missing. From our point of view, a milestone in testing and understanding the regulation of callose biosynthesis would be the purification of an active complex or subunit from the plasma membrane or its heterologous expression and subsequent in vitro analysis. Nevertheless, promising strategies have already been established that will promote research on callose biosynthesis, and include the application of super-resolution microscopy (Eggert et al., 2014) and the use of cultured cells (Srivastava et al., 2013).

Fig. 2.

Spheres of action in callose biosynthesis and regulation. Overview of four major spheres of action involved in callose biosynthesis and its regulation. Inside the spheres: aspects described for callose biosynthesis are described inside the spheres; aspects requiring further work in future projects (discussed within the text) are described outside the spheres.

Fig. 2.

Spheres of action in callose biosynthesis and regulation. Overview of four major spheres of action involved in callose biosynthesis and its regulation. Inside the spheres: aspects described for callose biosynthesis are described inside the spheres; aspects requiring further work in future projects (discussed within the text) are described outside the spheres.

LITERATURE CITED

Aist
JR
Baker
KF
Zentmeyer
GA
Cowling
EB
Annual Review of Phytopathology
Papillae and related wound plugs of plant cells
 
1976
Palo Alto
Annual Reviews
Alexandersson
E
Saalbach
G
Larsson
C
Kjellbom
P
Arabidopsis plasma membrane proteomics identifies components of transport, signal transduction and membrane trafficking
Plant and Cell Physiology
 
2004
45
1543
1556
An
C
Mou
Z
Salicylic acid and its function in plant immunity
Journal of Integrative Plant Biology
 
2011
53
412
428
An
Q
Hückelhoven
R
Kogel
KH
Van Bel
AJ
Multivesicular bodies participate in a cell wall-associated defence response in barley leaves attacked by the pathogenic powdery mildew fungus
Cellular Microbiology
 
2006
8
1009
1019
Andrawis
A
Solomon
M
Delmer
DP
Cotton fiber annexins: a potential role in the regulation of callose synthase
Plant Journal
 
1993
3
763
772
Aspinall
GO
Kessler
G
The structure of callose from the grape vine
Chemistry and Industry
 
1957
1296
Barratt
DH
Kolling
K
Graf
A
et al.  
Callose synthase GSL7 is necessary for normal phloem transport and inflorescence growth in Arabidopsis
Plant Physiology
 
2011
155
328
341
Beck
M
Zhou
J
Faulkner
C
MacLean
D
Robatzek
S
Spatio-temporal cellular dynamics of the Arabidopsis flagellin receptor reveal activation status-dependent endosomal sorting
Plant Cell
 
2012
24
4205
4219
Benschop
JJ
Mohammed
S
O'Flaherty
M
Heck
AJ
Slijper
M
Menke
FL
Quantitative phosphoproteomics of early elicitor signaling in Arabidopsis
Molecular and Cellular Proteomics
 
2007
6
1198
1214
Böhlenius
H
Mørch
SM
Godfrey
D
Nielsen
ME
Thordal-Christensen
H
The multivesicular body-localized GTPase ARFA1b/1c is important for callose deposition and ROR2 syntaxin-dependent preinvasive basal defense in barley
Plant Cell
 
2010
22
3831
3844
Boller
T
Felix
G
A renaissance of elicitors: perception of microbe-associated molecular patterns and danger signals by pattern-recognition receptors
Annual Review of Plant Biology
 
2009
60
379
406
Bolte
S
Talbot
C
Boutte
Y
Catrice
O
Read
ND
Satiat-Jeunemaitre
B
FM-dyes as experimental probes for dissecting vesicle trafficking in living plant cells
Journal of Microscopy
 
2004
214
159
173
Cai
G
Faleri
C
Del Casino
C
Emons
AM
Cresti
M
Distribution of callose synthase, cellulose synthase, and sucrose synthase in tobacco pollen tube is controlled in dissimilar ways by actin filaments and microtubules
Plant Physiology
 
2011
155
1169
1190
Calonge
TM
Arellano
M
Coll
PM
Perez
P
Rga5p is a specific Rho1p GTPase-activating protein that regulates cell integrity in Schizosaccharomyces pombe
Molecular Microbiology
 
2003
47
507
518
Chen
XY
Liu
L
Lee
E
et al.  
The Arabidopsis callose synthase gene GSL8 is required for cytokinesis and cell patterning
Plant Physiology
 
2009
150
105
113
Clay
NK
Adio
AM
Denoux
C
Jander
G
Ausubel
FM
Glucosinolate metabolites required for an Arabidopsis innate immune response
Science
 
2009
323
95
101
Currier
HB
Callose substance in plant cells
American Journal of Botany
 
1957
44
478
488
Daudi
A
Cheng
Z
O'Brien
JA
et al.  
The apoplastic oxidative burst peroxidase in Arabidopsis is a major component of pattern-triggered immunity
Plant Cell
 
2012
24
275
287
Dijkgraaf
GJ
Abe
M
Ohya
Y
Bussey
H
Mutations in Fks1p affect the cell wall content of β-1,3- and β-1,6-glucan in Saccharomyces cerevisiae
Yeast
 
2002
19
671
690
Dodds
PN
Rathjen
JP
Plant immunity: towards an integrated view of plant-pathogen interactions
Nature Reviews Genetics
 
2010
11
539
548
Dong
X
Hong
Z
Sivaramakrishnan
M
Mahfouz
M
Verma
DP
Callose synthase (CalS5) is required for exine formation during microgametogenesis and for pollen viability in Arabidopsis
Plant Journal
 
2005
42
315
328
Dong
X
Hong
Z
Chatterjee
J
Kim
S
Verma
DP
Expression of callose synthase genes and its connection with Npr1 signaling pathway during pathogen infection
Planta
 
2008
229
87
98
Douglas
CM
Foor
F
Marrinan
JA
et al.  
The Saccharomyces cerevisiae FKS1 (ETG1) gene encodes an integral membrane protein which is a subunit of 1,3-beta-D-glucan synthase
Proceedings of the National Academy of Sciences of the USA
 
1994
91
12907
12911
Drakakaki
G
van de Ven
W
Pan
S
et al.  
Isolation and proteomic analysis of the SYP61 compartment reveal its role in exocytic trafficking in Arabidopsis
Cell Research
 
2012
22
413
424
Dumas
C
Knox
RB
Callose and determination of pistil viability and incompatibility
Theoretical and Applied Genetics
 
1983
67
1
10
Dunkley
TP
Hester
S
Shadforth
IP
et al.  
Mapping the Arabidopsis organelle proteome
Proceedings of the National Academy of Sciences of the USA
 
2006
103
6518
6523
Edlund
AF
Swanson
R
Preuss
D
Pollen and stigma structure and function: the role of diversity in pollination
Plant Cell
 
2004
16
Suppl
S84
S97
Eggert
D
Naumann
M
Reimer
R
Voigt
CA
Nanoscale glucan polymer network causes pathogen resistance
Scientific Reports
 
2014
4
4159
Ellinger
D
Naumann
M
Falter
C
et al.  
Elevated early callose deposition results in complete penetration resistance to powdery mildew in Arabidopsis
Plant Physiology
 
2013
161
1433
1444
Ellis
RJ
Macdonald
IR
Specificity of cycloheximide in higher plant systems
Plant Physiology
 
1970
46
227
232
Enns
LC
Kanaoka
MM
Torii
KU
Comai
L
Okada
K
Cleland
RE
Two callose synthases, GSL1 and GSL5, play an essential and redundant role in plant and pollen development and in fertility
Plant Molecular Biology
 
2005
58
333
349
Erbs
G
Newman
MA
The role of lipopolysaccharide and peptidoglycan, two glycosylated bacterial microbe-associated molecular patterns (MAMPs), in plant innate immunity
Molecular Plant Pathology
 
2012
13
95
104
Erbs
G
Silipo
A
Aslam
S
et al.  
Peptidoglycan and muropeptides from pathogens Agrobacterium and Xanthomonas elicit plant innate immunity: structure and activity
Chemistry & Biology
 
2008
15
438
448
Eschrich
W
Kallose
Protoplasma
 
1956
47
487
530
Fabro
G
Steinbrenner
J
Coates
M
et al.  
Multiple candidate effectors from the oomycete pathogen Hyaloperonospora arabidopsidis suppress host plant immunity
PLoS Pathogens
 
2011
7
e1002348
Fei
H
Zhang
R
Pharis
RP
Sawhney
VK
Pleiotropic effects of the male sterile33 (ms33) mutation in Arabidopsis are associated with modifications in endogenous gibberellins, indole-3-acetic acid and abscisic acid
Planta
 
2004
219
649
660
Flors
V
Ton
J
van Doorn
R
Jakab
G
Garcia-Agustin
P
Mauch-Mani
B
Interplay between JA, SA and ABA signalling during basal and induced resistance against Pseudomonas syringae and Alternaria brassicicola
Plant Journal
 
2008
54
81
92
Geng
X
Cheng
J
Gangadharan
A
Mackey
D
The coronatine toxin of Pseudomonas syringae is a multifunctional suppressor of Arabidopsis defense
Plant Cell
 
2012
24
4763
4774
Gomez-Gomez
L
Felix
G
Boller
T
A single locus determines sensitivity to bacterial flagellin in Arabidopsis thaliana
Plant Journal
 
1999
18
277
284
Grobei
MA
Qeli
E
Brunner
E
et al.  
Deterministic protein inference for shotgun proteomics data provides new insights into Arabidopsis pollen development and function
Genome Research
 
2009
19
1786
1800
Gu
Y
Innes
RW
The KEEP ON GOING protein of Arabidopsis regulates intracellular protein trafficking and is degraded during fungal infection
Plant Cell
 
2012
24
4717
4730
Guseman
JM
Lee
JS
Bogenschutz
NL
et al.  
Dysregulation of cell-to-cell connectivity and stomatal patterning by loss-of-function mutation in Arabidopsis CHORUS (GLUCAN SYNTHASE-LIKE 8)
Development
 
2010
137
1731
1741
El Hadrami
A
Adam
LR
El Hadrami
I
Daayf
F
Chitosan in plant protection
Marine Drugs
 
2010
8
968
987
Harding
C
Heuser
J
Stahl
P
Receptor-mediated endocytosis of transferrin and recycling of the transferrin receptor in rat reticulocytes
Journal of Cell Biology
 
1983
97
329
339
Hartig
GL
Lehrbuch für Förster
 
1851
9th edn
Stuttgart
J.O. Gotta'scher
Han
X
Hyun
TK
Zhang
M
et al.  
Auxin-callose-mediated plasmodesmal gating is essential for tropic auxin gradient formation and signaling
Developmental Cell
 
2014
28
132
146
Hauck
P
Thilmony
R
He
SY
A Pseudomonas syringae type III effector suppresses cell wall-based extracellular defense in susceptible Arabidopsis plants
Proceedings of the National Academy of Sciences of the USA
 
2003
100
8577
8582
Hong
Z
Delauney
AJ
Verma
DP
A cell plate-specific callose synthase and its interaction with phragmoplastin
Plant Cell
 
2001a
13
755
768
Hong
Z
Zhang
Z
Olson
JM
Verma
DP
A novel UDP-glucose transferase is part of the callose synthase complex and interacts with phragmoplastin at the forming cell plate
Plant Cell
 
2001b
13
769
779
Hruz
T
Laule
O
Szabo
G
et al.  
Genevestigator v3: a reference expression database for the meta-analysis of transcriptomes
Advances in Bioinformatics
 
2008
2008
420747
Huang
XY
Niu
J
Sun
MX
et al.  
CYCLIN-DEPENDENT KINASE G1 is associated with the spliceosome to regulate CALLOSE SYNTHASE5 splicing and pollen wall formation in Arabidopsis
Plant Cell
 
2013
25
637
648
Ishiguro
J
Shibahara
K
Ueda
Y
Nakamura
K
Fission yeast TOR signaling is essential for the down-regulation of a hyperactivated stress-response MAP kinase under salt stress
Molecular Genetics and Genomics
 
2013
288
63
75
Jacobs
AK
Lipka
V
Burton
RA
et al.  
An Arabidopsis callose synthase, GSL5, is required for wound and papillary callose formation
Plant Cell
 
2003
15
2503
2513
Jones
JD
Dangl
JL
The plant immune system
Nature
 
2006
444
323
329
Keinath
NF
Kierszniowska
S
Lorek
J
et al.  
PAMP (pathogen-associated molecular pattern)-induced changes in plasma membrane compartmentalization reveal novel components of plant immunity
Journal of Biological Chemistry
 
2010
285
39140
39149
Keshavarzi
M
Soylu
S
Brown
I
et al.  
Basal defenses induced in pepper by lipopolysaccharides are suppressed by Xanthomonas campestris pv. vesicatoria
Molecular Plant-Microbe Interactions
 
2004
17
805
815
Kierszniowska
S
Seiwert
B
Schulze
WX
Definition of Arabidopsis sterol-rich membrane microdomains by differential treatment with methyl-beta-cyclodextrin and quantitative proteomics
Molecular & Cellular Proteomics
 
2009
8
612
623
Kim
MG
da Cunha
L
McFall
AJ
et al.  
Two Pseudomonas syringae type III effectors inhibit RIN4-regulated basal defense in Arabidopsis
Cell
 
2005
121
749
759
Kline
KG
Barrett-Wilt
GA
Sussman
MR
In planta changes in protein phosphorylation induced by the plant hormone abscisic acid
Proceedings of the National Academy of Sciences of the USA
 
2010
107
15986
15991
Koh
S
Andre
A
Edwards
H
Ehrhardt
D
Somerville
S
Arabidopsis thaliana subcellular responses to compatible Erysiphe cichoracearum infections
Plant Journal
 
2005
44
516
529
Kwon
C
Neu
C
Pajonk
S
et al.  
Co-option of a default secretory pathway for plant immune responses
Nature
 
2008
451
835
840
Lan
P
Li
W
Wen
TN
et al.  
iTRAQ protein profile analysis of Arabidopsis roots reveals new aspects critical for iron homeostasis
Plant Physiology
 
2011
155
821
834
Lee
AH
Middleton
MA
Guttman
DS
Desveaux
D
Phytopathogen type III effectors as probes of biological systems
Microbial Biotechnology
 
2013
6
230
240
Li
J
Zhao-Hui
C
Batoux
M
et al.  
Specific ER quality control components required for biogenesis of the plant innate immune receptor EFR
Proceedings of the National Academy of Sciences of the USA
 
2009
106
15973
15978
Lu
X
Tintor
N
Mentzel
T
et al.  
Uncoupling of sustained MAMP receptor signaling from early outputs in an Arabidopsis endoplasmic reticulum glucosidase II allele
Proceedings of the National Academy of Sciences of the USA
 
2009
106
22522
22527
Luna
E
Pastor
V
Robert
J
Flors
V
Mauch-Mani
B
Ton
J
Callose deposition: a multifaceted plant defense response
Molecular Plant-Microbe Interactions
 
2011
24
183
193
Marmagne
A
Ferro
M
Meinnel
T
et al.  
A high content in lipid-modified peripheral proteins and integral receptor kinases features in the arabidopsis plasma membrane proteome
Molecular & Cellular Proteomics
 
2007
6
1980
1996
Mauch-Mani
B
Mauch
F
The role of abscisic acid in plant-pathogen interactions
Current Opinion in Plant Biology
 
2005
8
409
414
McCann
HC
Nahal
H
Thakur
S
Guttman
DS
Identification of innate immunity elicitors using molecular signatures of natural selection
Proceedings of the National Academy of Sciences of the USA
 
2012
109
4215
4220
McCormick
S
Male gametophyte development
Plant Cell
 
1993
5
1265
1275
Micali
CO
Neumann
U
Grunewald
D
Panstruga
R
O'Connell
R
Biogenesis of a specialized plant-fungal interface during host cell internalization of Golovinomyces orontii haustoria
Cellular Microbiology
 
2011
13
210
226
Mitra
SK
Gantt
JA
Ruby
JF
Clouse
SD
Goshe
MB
Membrane proteomic analysis of Arabidopsis thaliana using alternative solubilization techniques
Journal of Proteome Research
 
2007
6
1933
1950
Mitra
SK
Walters
BT
Clouse
SD
Goshe
MB
An efficient organic solvent based extraction method for the proteomic analysis of Arabidopsis plasma membranes
Journal of Proteome Research
 
2009
8
2752
2767
Moreau
M
Degrave
A
Vedel
R
et al.  
EDS1 contributes to nonhost resistance of Arabidopsis thaliana against Erwinia amylovora
Molecular Plant-Microbe Interactions
 
2012
25
421
430
Nakagami
H
Sugiyama
N
Mochida
K
et al.  
Large-scale comparative phosphoproteomics identifies conserved phosphorylation sites in plants
Plant Physiology
 
2010
153
1161
1174
Naumann
M
Somerville
S
Voigt
C
Differences in early callose deposition during adapted and non-adapted powdery mildew infection of resistant Arabidopsis lines
Plant Signaling & behavior
 
2013
8
e24408
Nielsen
ME
Feechan
A
Böhlenius
H
Ueda
T
Thordal-Christensen
H
Arabidopsis ARF-GTP exchange factor, GNOM, mediates transport required for innate immunity and focal accumulation of syntaxin PEN1
Proceedings of the National Academy of Sciences of the USA
 
2012
109
11443
11448
Nishimura
MT
Stein
M
Hou
BH
Vogel
JP
Edwards
H
Somerville
SC
Loss of a callose synthase results in salicylic acid-dependent disease resistance
Science
 
2003
301
969
972
Nomura
K
Mecey
C
Lee
YN
Imboden
LA
Chang
JH
He
SY
Effector-triggered immunity blocks pathogen degradation of an immunity-associated vesicle traffic regulator in Arabidopsis
Proceedings of the National Academy of Sciences of the USA
 
2011
108
10774
10779
Nuhse
TS
Stensballe
A
Jensen
ON
Peck
SC
Large-scale analysis of in vivo phosphorylated membrane proteins by immobilized metal ion affinity chromatography and mass spectrometry
Molecular & Cellular Proteomics
 
2003
2
1234
1243
Nuhse
TS
Bottrill
AR
Jones
AM
Peck
SC
Quantitative phosphoproteomic analysis of plasma membrane proteins reveals regulatory mechanisms of plant innate immune responses
Plant Journal
 
2007
51
931
940
Pan
BT
Johnstone
RM
Fate of the transferrin receptor during maturation of sheep reticulocytes in vitro: selective externalization of the receptor
Cell
 
1983
33
967
978
Qadota
H
Python
CP
Inoue
SB
et al.  
Identification of yeast Rho1p GTPase as a regulatory subunit of 1,3-β-glucan synthase
Science
 
1996
272
279
281
Reiland
S
Messerli
G
Baerenfaller
K
et al.  
Large-scale Arabidopsis phosphoproteome profiling reveals novel chloroplast kinase substrates and phosphorylation networks
Plant Physiology
 
2009
150
889
903
Reiland
S
Finazzi
G
Endler
A
et al.  
Comparative phosphoproteome profiling reveals a function of the STN8 kinase in fine-tuning of cyclic electron flow (CEF)
Proceedings of the National Academy of Sciences of the USA
 
2011
108
12955
12960
Richmond
TA
Somerville
CR
The cellulose synthase superfamily
Plant Physiology
 
2000
124
495
498
Ryals
JA
Neuenschwander
UH
Willits
MG
Molina
A
Steiner
HY
Hunt
MD
Systemic acquired resistance
Plant Cell
 
1996
8
1809
1819
Samardakiewicz
S
Krzeslowska
M
Bilski
H
Bartosiewicz
R
Wozny
A
Is callose a barrier for lead ions entering Lemna minor L. root cells?
Protoplasma
 
2012
249
347
351
Scherp
P
Grotha
R
Kutschera
U
Occurrence and phylogenetic significance of cytokinesis-related callose in green algae, bryophytes, ferns and seed plants
Plant Cell Reports
 
2001
20
143
149
Schwacke
R
Schneider
A
van der Graaff
E
et al.  
ARAMEMNON, a novel database for Arabidopsis integral membrane proteins
Plant Physiology
 
2003
131
16
26
Sciaky
N
Presley
J
Smith
C
et al.  
Golgi tubule traffic and the effects of brefeldin A visualized in living cells
Journal of Cell Biology
 
1997
139
1137
1155
Senthil-Kumar
M
Mysore
KS
Nonhost resistance against bacterial pathogens: retrospectives and prospects
Annual Review of Phytopathology
 
2013
51
407
427
Sevilem
I
Miyashima
S
Helariutta
Y
Cell-to-cell communication via plasmodesmata in vascular plants
Cell Adhesion & Migration
 
2013
7
27
32
Srivastava
V
Malm
E
Sundqvist
G
Bulone
V
Quantitative proteomics reveals that plasma membrane microdomains from poplar cell suspension cultures are enriched in markers of signal transduction, molecular transport and callose biosynthesis
Molecular & Cellular Proteomics
 
2013
12
3874
3885
Stein
M
Dittgen
J
Sanchez-Rodriguez
C
et al.  
Arabidopsis PEN3/PDR8, an ATP binding cassette transporter, contributes to nonhost resistance to inappropriate pathogens that enter by direct penetration
Plant Cell
 
2006
18
731
746
Stone
B
Callose and related glucans
eLS
 
2006
Chichester
John Wiley & Sons
De Storme
N
De Schrijver
J
Van Criekinge
W
Wewer
V
Dormann
P
Geelen
D
GLUCAN SYNTHASE-LIKE8 and STEROL METHYLTRANSFERASE2 are required for ploidy consistency of the sexual reproduction system in Arabidopsis
Plant Cell
 
2013
25
387
403
Sugiyama
N
Nakagami
H
Mochida
K
et al.  
Large-scale phosphorylation mapping reveals the extent of tyrosine phosphorylation in Arabidopsis
Molecular Systems Biology
 
2008
4
193
Sun
A
Nie
S
Xing
D
Nitric oxide-mediated maintenance of redox homeostasis contributes to NPR1-dependent plant innate immunity triggered by lipopolysaccharides
Plant Physiology
 
2012
160
1081
1096
Thiele
K
Wanner
G
Kindzierski
V
et al.  
The timely deposition of callose is essential for cytokinesis in Arabidopsis
Plant Journal
 
2009
58
13
26
Töller
A
Brownfield
L
Neu
C
Twell
D
Schulze-Lefert
P
Dual function of Arabidopsis glucan synthase-like genes GSL8 and GSL10 in male gametophyte development and plant growth
Plant Journal
 
2008
54
911
923
Underwood
W
Zhang
S
He
SY
The Pseudomonas syringae type III effector tyrosine phosphatase HopAO1 suppresses innate immunity in Arabidopsis thaliana
Plant Journal
 
2007
52
658
672
Verma
DP
Hong
Z
Plant callose synthase complexes
Plant Molecular Biology
 
2001
47
693
701
Wang
D
Weaver
ND
Kesarwani
M
Dong
X
Induction of protein secretory pathway is required for systemic acquired resistance
Science
 
2005
308
1036
1040
Wang
L
Fobert
PR
Arabidopsis clade I TGA factors regulate apoplastic defences against the bacterial pathogen Pseudomonas syringae through endoplasmic reticulum-based processes
PLoS One
 
2013
8
e77378
Wheeler
H
Cell wall and plasmalemma modifications in diseased and injured plant tissue
Canadian Journal of Botany
 
1974
52
1005
1009
Wu
Y
Zhang
D
Chu
JY
et al.  
The Arabidopsis NPR1 protein is a receptor for the plant defense hormone salicylic acid
Cell Reports
 
2012
1
639
647
Xie
B
Wang
X
Hong
Z
Precocious pollen germination in Arabidopsis plants with altered callose deposition during microsporogenesis
Planta
 
2010
231
809
823
Xie
B
Wang
X
Zhu
M
Zhang
Z
Hong
Z
CalS7 encodes a callose synthase responsible for callose deposition in the phloem
Plant Journal
 
2011
65
1
14
Xie
B
Deng
Y
Kanaoka
MM
Okada
K
Hong
Z
Expression of Arabidopsis callose synthase 5 results in callose accumulation and cell wall permeability alteration
Plant Science
 
2012
183
1
8
Yang
J
Tian
L
Sun
MX
et al.  
AUXIN RESPONSE FACTOR17 is essential for pollen wall pattern formation in Arabidopsis
Plant Physiology
 
2013
162
720
731
Zhang
J
Shao
F
Li
Y
et al.  
A Pseudomonas syringae effector inactivates MAPKs to suppress PAMP-induced immunity in plants
Cell Host & Microbe
 
2007
1
175
185
Zhang
ZJ
Peck
SC
Simplified enrichment of plasma membrane proteins for proteomic analyses in Arabidopsis thaliana
Proteomics
 
2011
11
1780
1788
Zhou
J
Spallek
T
Faulkner
C
Robatzek
S
CalloseMeasurer: a novel software solution to measure callose deposition and recognise spreading callose patterns
Plant Methods
 
2012
8
49
Zimmerli
L
Stein
M
Lipka
V
Schulze-Lefert
P
Somerville
S
Host and non-host pathogens elicit different jasmonate/ethylene responses in Arabidopsis
Plant Journal
 
2004
40
633
646

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