title: HYPERSENSITIVE TO RED AND BLUE 1 and its C-terminal regulatory function control FLOWERING LOCUS T expression.
abstract: The red and far-red light-absorbing phytochromes and UV-A/blue light-absorbing cryptochromes regulate seedling de-etiolation and flowering responses. The signaling steps that mediate the photoreceptor regulation on key flowering genes remain largely unknown. We report that a previously identified photomorphogenic mutant, hypersensitive to red and blue 1 (hrb1), flowered late and showed attenuated expression of FLOWERING LOCUS T (FT) over both long days and short days. Transgenic plants that overexpress the full-length HRB1, or its C-terminal half, flowered early and accumulated more FT messages under short-day conditions. The transgenic plants also displayed hyposensitive de-etiolation phenotypes, and the expression of these phenotypes requires the action of PIF4. The double mutant of hrb1/cry2 showed a flowering phenotype and an FT expression pattern similar to hrb1 under long-day conditions, suggesting that HRB1 may function downstream of cry2 under long-day conditions. In contrast, hrb1/phyB-9 showed a flowering phenotype and an FT expression pattern similar to phyB-9 over both long days and short days, indicating a modulatory role of HRB1 in the flowering pathway mediated by phyB. Overexpression of HRB1 did not affect the expression of the central clock oscillators, TOC1 and CCA1. HRB1 therefore represents a signaling step that regulates FT expression downstream of red and blue light perception.
authors.affiliation: Department of Plant Biology, University of Minnesota, St Paul, MN 55108, USA.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Kang
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhou
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Sun
authors.forename: Min
authors.initials: M
authors.lastname: Ni
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism / Q000502:physiology; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D018548:Cotyledon / Q000254:growth & development / Q000378:metabolism; D056931:Cryptochromes; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000254:growth & development / Q000378:metabolism; D008027:Light; D009154:Mutation; D010641:Phenotype; D051939:Phytochrome B / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism / Q000528:radiation effects; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000217:Acyltransferases; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins; D056931:Cryptochromes; D051939:Phytochrome B; D014157:Transcription Factors; C114425:CCA1 protein, Arabidopsis; C103618:CRY2 protein, Arabidopsis; C418905:FT protein, Arabidopsis; C526697:HRB1 protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C459466:PIF4 protein, Arabidopsis; C411822:TOC1 protein, Arabidopsis; C491135:AT5G13930 protein, Arabidopsis