PIL5, a Phytochrome-Interacting bHLH Protein, Regulates Gibberellin Responsiveness by Binding Directly to theGAIandRGAPromoters inArabidopsisSeeds | Zendy

Eunkyoo Oh | Zendy; Shinjiro Yamaguchi | Zendy; Jianhong Hu | Zendy; Yusuke Jikumaru | Zendy; Byunghyuck Jung | Zendy; Inyup Paik | Zendy; HeeSeung Lee | Zendy; Taiping Sun | Zendy; Yuji Kamiya | Zendy; Giltsu Choi | Zendy

Open Access

PIL5, a Phytochrome-Interacting bHLH Protein, Regulates Gibberellin Responsiveness by Binding Directly to theGAIandRGAPromoters inArabidopsisSeeds

Author(s) -

Eunkyoo Oh,

Shinjiro Yamaguchi,

Jianhong Hu,

Yusuke Jikumaru,

Byunghyuck Jung,

Inyup Paik,

HeeSeung Lee,

Taiping Sun,

Yuji Kamiya,

Giltsu Choi

Publication year - 2007

Publication title -

the plant cell

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 5.324

H-Index - 341

eISSN - 1532-298X

pISSN - 1040-4651

DOI - 10.1105/tpc.107.050153

Subject(s) - phytochrome , gibberellin , repressor , biology , abscisic acid , arabidopsis , promoter , gene , catabolism , gibberellic acid , psychological repression , transcription (linguistics) , microbiology and biotechnology , transcription factor , germination , regulation of gene expression , gene expression , biochemistry , mutant , genetics , metabolism , botany , linguistics , philosophy , red light

Previous work showed that PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5), a light-labile basic helix-loop-helix protein, inhibits seed germination by repressing GIBBERELLIN 3beta-HYDROXYLASE1 (GA3ox1) and GA3ox2 and activating a gibberellic acid (GA) catabolic gene (GA2ox2). However, we show persistent light-dependent and PIL5-inhibited germination behavior in the absence of both de novo GA biosynthesis and deactivation by GA2ox2, suggesting that PIL5 regulates not only GA metabolism but also GA responsiveness. PIL5 increases the expression of two GA repressor (DELLA) genes, GA-INSENSITIVE (GAI) and REPRESSOR OF GA1-3 (RGA/RGA1), in darkness. The hypersensitivity of gai-t6 rga-28 to red light and the suppression of germination defects of a rga-28 PIL5 overexpression line show the significant role of this transcriptional regulation in seed germination. PIL5 also increases abscisic acid (ABA) levels by activating ABA biosynthetic genes and repressing an ABA catabolic gene. PIL5 binds directly to GAI and RGA promoters but not to GA and ABA metabolic gene promoters. Together, our results show that light signals perceived by phytochromes cause a reduction in the PIL5 protein level, which in turn regulates the transcription of two DELLA genes directly and that of GA and ABA metabolic genes indirectly.

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