The light perception in seedlings modulates the post-embryonic development,integrating phytohormone and other endogenous responses with environmental cues. Aproper hypocotyl elongation at the first hours/days of development is critical for plantestablishment and photosynthetic success. The precise coordination of hypocotylelongation is under parallel and redundant regulatory pathways. Gene expression, atspecific cells, modulated by photoreceptors and phytohormones, is the main regulatorymechanism at this phase. However, the integrative pathways controlling hypocotyldevelopment are not completely elucidated. Our previous results showed that themiRNA156/SPL9 module is associated with hypocotyl elongation control. Wehypothesized that this module acts as a regulatory hub in gibberellin (GA),brassinosteroid (BR), and light crosstalk. We already generated several data indicatingthat SPL9 expression is modulated by GA and BR, and perhaps by light duringhypocotyl elongation. The BEPE project proposes to evaluate in greater detail thehypocotyl phenotype and transcriptome alterations in Arabidopsis miR156/SPL9mutants and transgenic lines under distinct light regimes. The hypocotyl length fromseedlings growing in high red/far-red, and low blue/UV-A light will show whether thephenotype observed in SPL9 gain or loss of function is dependent on the light quality.Moreover, transcriptome analyses of specific cells in the hypocotyl expansion zoneunder distinct light regimes will provide important insights into the SPL9 function as anactivator and/or repressor of light responses. The use of SPL9-GFP transgenic plantswill allow the discovery of direct targets by ChIP-qPCR. Finally, the combination ofRNA-seq and ChIP-qPCR will allow the discovery of SPL9 direct targets, which maybe modulated by BR, GA, and light in the hypocotyl.
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