title: Overexpression of a mutant basic helix-loop-helix protein HFR1, HFR1-deltaN105, activates a branch pathway of light signaling in Arabidopsis.
abstract: The HFR1, a basic helix-loop-helix protein, is required for a subset of phytochrome A-mediated photoresponses in Arabidopsis. Here, we show that overexpression of the HFR1-deltaN105 mutant, which lacks the N-terminal 105 amino acids, confers exaggerated photoresponses even in darkness. Physiological analysis implied that overexpression of HFR1-deltaN105 activated constitutively a branch pathway of light signaling that mediates a subset of photomorphogenic responses, including germination, de-etiolation, gravitropic hypocotyl growth, blocking of greening, and expression of some light-regulated genes such as CAB, DRT112, PSAE, PSBL, PORA, and XTR7, without affecting the light-responsiveness of anthocyanin accumulation and expression of other light-regulated genes such as CHS and PSBS. Although the end-of-day far-red light response and petiole elongation were suppressed in the HFR1-deltaN105-overexpressing plants, flowering time was not affected by HFR1-deltaN105. In addition, the HFR1-deltaN105-overexpressing plants showed hypersensitive photoresponses in the inhibition of hypocotyl elongation, dependently on phytochrome A, FHY1, and FHY3 under FR light or phyB under R light, respectively. Moreover, our double mutant analysis suggested that the hypersensitive photoresponse is due to functional cooperation between HFR1-deltaN105 and other light-signaling components including HY5, a basic leucine zipper protein. Taken together, our results of gain-of-function approach with HFR1-deltaN105 suggest the existence of a complex and important basic helix-loop-helix protein-mediated transcriptional network controlling a branch pathway of light signaling and provide a useful framework for further genetic dissection of light-signaling network in Arabidopsis.
authors.affiliation: Kumho Life and Environmental Science Laboratory, 1 Oryong-Dong, Buk-Gu, Gwangju 500-712, Republic of Korea.
authors.forename: Ki-Young
authors.initials: KY
authors.lastname: Yang
authors.forename: Young-Mi
authors.initials: YM
authors.lastname: Kim
authors.forename: Seunghee
authors.initials: S
authors.lastname: Lee
authors.forename: Pill-Soon
authors.initials: PS
authors.lastname: Song
authors.forename: Moon-Soo
authors.initials: MS
authors.lastname: Soh
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics*; D004307:Dose-Response Relationship, Radiation; D018506:Gene Expression Regulation, Plant / Q000235:genetics* / Q000528:radiation effects; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D008027:Light; D009149:Mustard Plant / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017384:Sequence Deletion; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C414438:At1g02340 protein, Arabidopsis