Phytochrome Photosensory Signaling and Transcriptional Networks

ITQB Seminar

Title:Phytochrome Photosensory Signaling and Transcriptional Networks
Speaker: Peter H. Quail  (http://pmb.berkeley.edu/profile/pquail)

Affiliation: Plant and Microbial Biology, U.C. Berkeley, and Plant Gene Expression Center, Albany CA 94710

Host: Nelson Saibo-Genomics of Plant Stress Laboratory

Abstract:

Current evidence indicates that the phytochrome (phy) signaling process involves rapid translocation of the light-activated photoreceptor into the nucleus, where it interacts with specific bHLH transcription factors, termed Phytochrome-Interacting Factors (PIFs), inducing transcriptional responses in target genes. We have shown that a quadruple pif mutant (pif1pif3pif4pif5 (pifq)) exhibits a cop-like phenotype in dark-grown seedlings, indicating that these transcription factors collectively repress photomorphogenesis in post-germinative darkness, and that photoactivated phy reverses this repression by inducing rapid phosphorylation and subsequent degradation of the PIFs upon initial light exposure. Previously, using targeted and random mutagenesis, we identified binding sites on phyB and PIF3 necessary for productive signaling interactions in vivo. Recently, we have defined residues within the PIF3 protein that are targets of light-induced phosphorylation. Using genome-wide transcriptome analysis of wild-type and pifq seedlings, we have identified PIF-regulated genes that respond rapidly and reciprocally, in a PIF-dependent manner, to phy photoactivation and deactivation upon initial light-exposure and vegetative-shade exposure, respectively. Coupled with ChIP-seq analysis, these data have permitted identification of potential direct targets of the phy-PIF signaling system. Interestingly, increasing evidence indicates that the PIFs have a role in multiple signaling pathways, in addition to light, thereby suggesting that they function as components of a central cellular signaling hub.