Central clock components modulate plant shade avoidance by directly repressing transcriptional activation activity of PIF proteins ($) (PNAS)

PHYTOCHROME INTERACTING FACTORs (PIFs) are transcriptional factors that relay light signals from the phytochrome photoreceptors to regulate the expression of light-sensitive genes, but there is not a direct correlation between PIF binding and expression of the target genes. In this paper, Zhang Y et al. identified additional regulatory proteins that influence PIF-mediated transcription. Starting with computational predictions from ChiP-seq data, the authors found that key proteins involved in the central clock, Pseudo-Response Regulators 5 and 7 (PRR5 and PRR7) affect PIF transcriptional activity. In shade, pif mutants show reduced hypocotyl elongation, and in contrast prr mutants exhibit elongated hypocotyls, indicating an important role for these PRR clock components in light responses and hypocotyl elongation. Expression analysis of PIF-regulated genes in prr mutants showed altered gene expression suggesting PRRs repress the PIF induced gene expression. The formation of a PIF-PRR complex shows a physical interaction between PRR and PIF in the nucleus to repress PIF activity, and a direct link between the clock and light-regulated gene expression. (Summary by Suresh Damodaran) PNAS  10.1073/pnas.1918317117