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JA and SA signaling components are required for shade avoidance

Julin Maloof: University of California

<div>Plants have sophisticated mechanisms for sensing neighbor shade and responding through enhanced elongation and physiological changes to maximize their ability to compete for light. The shade avoidance response affects many organs and growth stages, yet the signaling pathways have mostly been studied in seedlings. To understand the signaling pathways in older plants, we performed phenotypic profiling and a gene expression time course of adult shade avoidance in wild-type and shade avoidance mutants. With this data we established a signaling cascade of hormone action during wild-type response to shade and used mutants to determine how genetic perturbation affects the cascade. One finding was that <em>MYC2</em>, central to jasmonic acid signaling, is also required for shade induced petiole elongation. A second finding was that we found pervasive misregulation of salicylic acid genes in many mutants, suggesting salicylic acid signaling to be an important shade avoidance growth regulator. Supporting this hypothesis, several salicylic acid pathway mutants reduced shade-induced and basal growth. The effect of these mutants on shade avoidance was specific to petiole elongation, thereby defining important stage-specific differences in the downstream shade avoidance signaling pathway. Shade treatment did not change salicylic acid levels, indicating salicylic acid mediation of shade avoidance is not dependent on modulation of salicylic acid levels.</div>

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