title: Definition of early transcriptional circuitry involved in light-induced reversal of PIF-imposed repression of photomorphogenesis in young Arabidopsis seedlings.
abstract: Light signals perceived by the phytochromes induce the transition from skotomorphogenic to photomorphogenic development (deetiolation) in dark-germinated seedlings. Evidence that a quadruple mutant (pifq) lacking four phytochrome-interacting bHLH transcription factors (PIF1, 3, 4, and 5) is constitutively photomorphogenic in darkness establishes that these factors sustain the skotomorphogenic state. Moreover, photoactivated phytochromes bind to and induce rapid degradation of the PIFs, indicating that the photoreceptor reverses their constitutive activity upon light exposure, initiating photomorphogenesis. Here, to define the modes of transcriptional regulation and cellular development imposed by the PIFs, we performed expression profile and cytological analyses of pifq mutant and wild-type seedlings. Dark-grown mutant seedlings display cellular development that extensively phenocopies wild-type seedlings grown in light. Similarly, 80% of the gene expression changes elicited by the absence of the PIFs in dark-grown pifq seedlings are normally induced by prolonged light in wild-type seedlings. By comparing rapidly light-responsive genes in wild-type seedlings with those responding in darkness in the pifq mutant, we identified a subset, enriched in transcription factor-encoding genes, that are potential primary targets of PIF transcriptional regulation. Collectively, these data suggest that the transcriptional response elicited by light-induced PIF proteolysis is a major component of the mechanism by which the phytochromes pleiotropically regulate deetiolation and that at least some of the rapidly light-responsive genes may comprise a transcriptional network directly regulated by the PIF proteins.
authors.affiliation: Department of Plant and Microbial Biology, University of California-Berkeley, CA 94720, USA.
authors.forename: Pablo
authors.initials: P
authors.lastname: Leivar
authors.forename: James M
authors.initials: JM
authors.lastname: Tepperman
authors.forename: Elena
authors.initials: E
authors.lastname: Monte
authors.forename: Robert H
authors.initials: RH
authors.lastname: Calderon
authors.forename: Tiffany L
authors.initials: TL
authors.lastname: Liu
authors.forename: Peter H
authors.initials: PH
authors.lastname: Quail
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D003624:Darkness; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000528:radiation effects; D008027:Light; D055537:Light Signal Transduction / Q000235:genetics; D009024:Morphogenesis / Q000235:genetics* / Q000528:radiation effects; D009154:Mutation / Q000235:genetics; D010775:Photic Stimulation; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D036226:Seedlings / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics* / Q000528:radiation effects; D015533:Transcriptional Activation / Q000235:genetics / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D010834:Phytochrome; D014157:Transcription Factors; C508068:At2g20180 protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis; C459466:PIF4 protein, Arabidopsis; C497729:PIF5 protein, Arabidopsis