Volume 25, Issue 1, January 2013

A high-throughput imaging platform and custom algorithm are presented for the quantitative analysis of complex plasmodesmata (PD) formation. Complex PDs are shown to be derived from simple PDs in a pattern that is accelerated when leaves undergo the sink–source transition. This approach will facilitate further large-scale analyses of the endogenous and exogenous factors that influence PD formation.

The role of HAN in regulating floral development was examined in Arabidopsis. HAN represses hundreds of genes, especially genes involved in hormone responses and floral organ specification. Overexpression of HAN represses the expression of HAN and other GATA3 family genes (HANL2, GNC, and GNL), forming a negative regulatory loop, and thus serves as a key repressor regulating floral development.

It has been assumed that only seed plants are able to sense far-red light as PHYA, which is essential for far-red light perception, specifically evolved in seed plants. Here, we show that also cryptogams, such as mosses and ferns, respond to far-red light and have phytochromes with PHYA-like properties. This suggests that far-red light sensing is an evolutionarily ancient trait.

Photoreceptors usually repress seedling hypocotyl elongation under light, whereas PHYB overexpression causes longer hypocotyls than in the wild type under far-red light. This work demonstrates that phyB forms a protein complex with SPA1 through a direct interaction to promote its nuclear accumulation, enhancing hypocotyl elongation in response to far-red light.

HDA19 interacts with HSL1 and together they negatively regulate seed maturation gene expression in vegetative organs, suggesting that epigenetic regulation is critical for seed development. This study provides insight into the molecular mechanism underlying the gene regulation in seed development.

This work identifies two seed dormancy regulators SIN3-LIKE1 (SNL1) and SNL2 that can interact with histone deacetylase to modify histone acetylation abundance of transcribed genes. SNL1 and SNL2 are redundantly involved in the regulation of seed dormancy via antagonism of abscisic acid and ethylene mediated by histone deacetylation.

Conditional repression of two essential chloroplast genes involved in plastid transcription and translation in the alga Chlamydomonas reinhardtii leads to cell growth arrest and overaccumulation of many plastid transcripts. It also identifies multiple negative regulatory chloroplast feedback loops and alters expression of nuclear genes implicated in chloroplast biogenesis, protein turnover, and stress.

The xylem in Arabidopsis roots develops as a single row of cells neighboring the undifferentiated procambium. This work determined that two closely related AHL3 and AHL4 transcription factors regulate the boundaries between the xylem and procambium. AHL4 moves from the procambium to xylem in the root meristem, likely as a heteromeric complex with AHL3.

The export of auxin by ABCB-type auxin transporters is essential for proper plant development and is regulated by TWISTED DWARF1. This work shows that in addition to the endoplasmic reticulum, TWISTED DWARF1 is also located at lateral plasma membrane subdomains where it colocalizes and interacts with ABCB1; the data support a model in which TWISTED DWARF1 promotes lateral ABCB1-mediated auxin efflux at the plasma membrane.

Diatom cell division is controlled by light. In this work, the diatom-specific cyclin dsCYC2 is identified as a rate-limiting factor that controls the onset of the cell cycle in response to blue light. Strikingly, dsCYC2 expression is under the direct control of an aureochrome blue light receptor.

This work reports that FCP1, encoding a CLE protein, negatively regulates the maintenance of the vegetative shoot apical meristem in rice. In addition, it reveals that WOX4 promotes the undifferentiated state of the meristem and is negatively regulated by FCP1.

Light inhibits hypocotyl growth and the expression of genes that stimulate it. This study reveals that the CHD3 chromatin remodeling factor PKL/EPP1 is recruited by HY5, a master transcription factor of the light signaling pathway and represses H3K27me3 modification of cell elongation–related loci. PKL/EPP1 and HY5 work together to fine-tune hypocotyl cell elongation in response to light.

HDA18 has deacetylase activity and affects epidermal cell patterning of Arabidopsis roots by regulating the transcription of a set of kinase genes. This set of kinase genes functions in a positional information relay system. Both down- and upregulation of HDA18 expression result in the same phenotype and increase the expression the kinase genes.

Pectin and xylan are generally considered as separate cell wall glycan networks distinct from cell wall proteins. This work describes a cell wall proteoglycan with pectin and arabinoxylan covalently attached to an arabinogalactan protein, identifying a cross-linked matrix polysaccharide wall protein architecture with implications for wall structure, function, and synthesis.

This study reports on the physiological role of the TPP riboswitch noncoding RNA element in balancing thiamin levels, plant metabolism, and overall organismal fitness. The model suggests that in Arabidopsis, the THIC promoter and the riboswitch simultaneously tightly regulate thiamin biosynthesis in a circadian manner and consequently sense and control vital points of core cellular metabolism.

Djarly, a natural Arabidopsis mutant defective in seed mucilage release, is shown to be defective in a pectin methylesterase inhibitor, PMEI6. Mutant and overexpressor phenotypes highlight the importance of modulating the degree of homogalacturonan methylesterification for correct primary cell wall fragmentation and pectin partitioning into adherent and soluble mucilage layers.

This work examines the role of tissue-specific abscisic acid signaling in the response of the root to salt, finding that salt stress affects root system architecture in seedlings by inhibiting lateral root development through a signaling pathway active in the endodermis.

This article characterizes RCF1, a cold-inducible DEAD box RNA helicase that is important for pre-mRNA splicing of genes. RCF1 regulates the expression of cold-regulated genes and is vital for cold tolerance in plants.