Optimum of flowering time is most important for modern agricultural production system, especially for crops yield and seeds quality. Furthermore, during the lifecycle of a plant, one of the most attractive biological processes in plant research field is the transition from the vegetative to the reproductive stage. Consequently, flowering time control is an important research field in plant biology. In Arabidopsis, flowering time is precisely controlled by extensive environmental and internal cues. Gibberellins (GA) promote flowering, while abscisic acid (ABA) is considered as a flowering suppressor. Currently, the mechanisms underlying the promotion effect of GA on flowering transition is studies extensively and intensively. However, the detailed mechanism through which ABA inhibits floral transition is poorly understood.

We recently found that ABA inhibits floral transition by activating FLC transcription through ABSCISIC ACID-INSENSITIVE 4 (ABI4) with solid evidences including genetics, molecular biology, plant physiology and biochemical data. Consequently, ABI4 also is the second indentified gene regulating plant floral transition in ABA signaling pathway, after ABI5.

Firstly, the authors demonstrated that the abi4 mutant showed the early flowering phenotype whereas the over-expression ABI4 (OE-ABI4) plant delayed floral transition. Consistently, qRT-PCR assay revealed that the FLC transcription level was downregulated in abi4, but upregulated in OE-ABI4. The change of FT level was consistent with the pattern of FLC expression. Following Chromatin immunoprecipitation qPCR (ChIP-qPCR), Electrophoretic Mobility Shift Assays (EMSA) and tobacco transient expression analysis showed that ABI4 promotes FLC expression by directly binding to its promoter. Further, genetic analysis demonstrated that OE-ABI4::flc-3 could not alter the flc-3 phenotype. OE-FLC::abi4 showed a markedly delayed-flowering phenotype, which mimicked OE-FLC::WT, and suggested that ABI4 acts upstream on FLC in the same genetic pathway. In a word, these available evidences suggest that ABA inhibits floral transition by activating FLC transcription through ABI4.

Publication

ABSCISIC ACID-INSENSITIVE 4 negatively regulates flowering through directly promoting Arabidopsis FLOWERING LOCUS C transcription.
Shu K, Chen Q, Wu Y, Liu R, Zhang H, Wang S, Tang S, Yang W, Xie Q
J Exp Bot. 2016 Jan

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