title: A circadian clock- and PIF4-mediated double coincidence mechanism is implicated in the thermosensitive photoperiodic control of plant architectures in Arabidopsis thaliana.
abstract: In Arabidopsis thaliana, the circadian clock regulates diurnal and photoperiodic plant growth including the elongation of hypocotyls in a time-of-day-specific and short-day (SD)-specific manner. The clock-controlled PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) encoding a basic helix-loop-helix (bHLH) transcription factor plays crucial roles in this regulation. PIF4 is transcribed precociously at the end of the night in SDs, under which conditions the protein product is stably accumulated, while PIF4 is expressed exclusively during the daytime in long days (LDs), under which conditions the protein product is degraded by light-activated phytochrome B. The dawn- and SD-specific elongation of hypocotyls is best explained by the coincident accumulation of the active PIF4 protein during the night-time before dawn specifically in SDs. However, this coincidence model was challenged with the recent finding that the elongation of hypocotyls is markedly promoted at high growth temperature (i.e. 28°C) even under LDs in a PIF4-dependent manner. Here, we reconciled these apparently conflicting facts by showing that the transcription of PIF4 occurs precociously at the end of the night-time at 28°C in LDs, similarly to in SDs. Both the events resulted in the same consequence, i.e. that a set of PIF4 target genes (ATHB2, GH3.5, IAA19, IAA29, BRox2, GAI, ACS8 and CKX5) was induced accordingly in a time-of-day-specific manner. Taken together, we propose an extended double coincidence mechanism, by which the two environmental cues (i.e. photoperiods and temperatures), both of which vary on a season to season basis, are integrated into the same clock- and PIF4-mediated output pathway and regulate a hormone signaling network to fit plant architectures properly to domestic habitats.
authors.affiliation: Laboratory of Molecular and Functional Genomics, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nomoto
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Nomoto
authors.forename: Saori
authors.initials: S
authors.lastname: Kubozono
authors.forename: Miki
authors.initials: M
authors.lastname: Miyachi
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yamashino
authors.forename: Norihito
authors.initials: N
authors.lastname: Nakamichi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
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*; D057906:Circadian Clocks; D002940:Circadian Rhythm; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008954:Models, Biological; D017440:Photoperiod; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D015398:Signal Transduction; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D059467:Transcriptome
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; D051939:Phytochrome B; D014157:Transcription Factors; C080210:ATHB-2 protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C459466:PIF4 protein, Arabidopsis