title: Molecular convergence of clock and photosensory pathways through PIF3-TOC1 interaction and co-occupancy of target promoters.
abstract: A mechanism for integrating light perception and the endogenous circadian clock is central to a plant's capacity to coordinate its growth and development with the prevailing daily light/dark cycles. Under short-day (SD) photocycles, hypocotyl elongation is maximal at dawn, being promoted by the collective activity of a quartet of transcription factors, called PIF1, PIF3, PIF4, and PIF5 (phytochrome-interacting factors). PIF protein abundance in SDs oscillates as a balance between synthesis and photoactivated-phytochrome-imposed degradation, with maximum levels accumulating at the end of the long night. Previous evidence shows that elongation under diurnal conditions (as well as in shade) is also subjected to circadian gating. However, the mechanism underlying these phenomena is incompletely understood. Here we show that the PIFs and the core clock component Timing of CAB expression 1 (TOC1) display coincident cobinding to the promoters of predawn-phased, growth-related genes under SD conditions. TOC1 interacts with the PIFs and represses their transcriptional activation activity, antagonizing PIF-induced growth. Given the dynamics of TOC1 abundance (displaying high postdusk levels that progressively decline during the long night), our data suggest that TOC1 functions to provide a direct output from the core clock that transiently constrains the growth-promoting activity of the accumulating PIFs early postdusk, thereby gating growth to predawn, when conditions for cell elongation are optimal. These findings unveil a previously unrecognized mechanism whereby a core circadian clock output signal converges immediately with the phytochrome photosensory pathway to coregulate directly the activity of the PIF transcription factors positioned at the apex of a transcriptional network that regulates a diversity of downstream morphogenic responses.
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain;
authors.forename: Judit
authors.initials: J
authors.lastname: Soy
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain; Bioengineering Department, Institut Químic de Sarrià School of Engineering, 08017 Barcelona, Spain;
authors.forename: Pablo
authors.initials: P
authors.lastname: Leivar
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain;
authors.forename: Nahuel
authors.initials: N
authors.lastname: González-Schain
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain;
authors.forename: Guiomar
authors.initials: G
authors.lastname: Martín
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain;
authors.forename: Céline
authors.initials: C
authors.lastname: Diaz
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain;
authors.forename: Maria
authors.initials: M
authors.lastname: Sentandreu
authors.affiliation: Departmentt of Plant and Microbial Biology, University of California, Berkeley, CA 94720; Plant Gene Expression Center, Agriculture Research Service, US Department of Agriculture, Albany, CA 94710.
authors.forename: Bassem
authors.initials: B
authors.lastname: Al-Sady
authors.affiliation: Departmentt of Plant and Microbial Biology, University of California, Berkeley, CA 94720; Plant Gene Expression Center, Agriculture Research Service, US Department of Agriculture, Albany, CA 94710 quail@berkeley.edu elena.monte@cragenomica.es.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Quail
authors.affiliation: Center for Research in Agricultural Genomics, Consejo Superior de Investigaciones Científicas (CRAG, CSIC), Bellaterra, 08193 Barcelona, Spain; quail@berkeley.edu elena.monte@cragenomica.es.
authors.forename: Elena
authors.initials: E
authors.lastname: Monte
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000502:physiology*; D051792:Basic Helix-Loop-Helix Proteins / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D017343:Genes, Plant; D011401:Promoter Regions, Genetic / Q000235:genetics*; D025941:Protein Interaction Mapping; D036226:Seedlings / Q000254:growth & development; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D014157:Transcription Factors; C116162:PIF3 protein, Arabidopsis; C411822:TOC1 protein, Arabidopsis
keywords: PIFs; TOC1; circadian clock; gating of growth; photoperiod