Abstract
Plants have evolved strategies to avoid shade and optimize the capture of sunlight. While some species are tolerant to shade, plants such as Arabidopsis thaliana are shade-intolerant and induce elongation of their hypocotyl to outcompete neighboring plants. We report the identification of a developmental module acting downstream of shade perception controlling vascular patterning. We show that Arabidopsis plants react to shade by increasing the number and types of water-conducting tracheary elements in the vascular cylinder to maintain vascular density constant. Mutations in genes affecting vascular patterning impair the production of additional xylem and also show defects in the shade-induced hypocotyl elongation response. Comparative analysis of the shade-induced transcriptomes revealed differences between wild type and vascular patterning mutants and it appears that the latter mutants fail to induce sets of genes encoding biosynthetic and cell wall modifying enzymes. Our results thus set the stage for a deeper understanding of how growth and patterning are coordinated in a dynamic environment.
Highlights
Shade intolerant plants such as Arabidopsis respond to subtle changes in the red (R) to far-red (FR) light ratio (R:FR) by increasing hypocotyl elongation growth to outcompete shade caused by neighboring plants
We find that the REVOLUTA (REV) and KANADI1 (KAN1) transcription factors which are primarily involved in patterning the early leaf, impinge on the regulation of WUSCHEL HOMEOBOX4 (WOX4), another transcription factor involved in vascular development
In white light conditions, when the R:FR ratio is high, PHYTOCHROME B (PHYB) is active in the nucleus where it maintains the continuous degradation of PHYTOCHROME-INTERACTING FACTORs (PIFs) transcription factors [5]
Summary
Shade intolerant plants such as Arabidopsis respond to subtle changes in the red (R) to far-red (FR) light ratio (R:FR) by increasing hypocotyl elongation growth to outcompete shade caused by neighboring plants. Genome-wide transcription factor binding site studies focusing on the master patterning factors of the class III homeodomain leucine zipper (HD-ZIPIII) as well as on KANADI families revealed several direct target genes with known roles in the shade avoidance response [18,19,20]. These HD-ZIPIII proteins interact with the rapid shade-response HD-ZIPII transcription factors to regulate leaf patterning [21,22,23]
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