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 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. However, the detailed mechanism through which ABA inhibits floral transition is poorly understood.

 

Dr. XIE Qi’s group in the Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences, recently reported that ABA inhibits floral transition by activating FLOWERING LOCUS C (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 identified gene regulating plant floral transition in ABA signaling pathway, after ABI5.

 

Firstly, the researchers demonstrated that the abi4 mutant showed the early flowering phenotype whereas the ABI4-overexpressing (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.

 

The study entitled “ABSCISIC ACID-INSENSITIVE 4 negatively regulates flowering through directly promoting Arabidopsis FLOWERING LOCUS Ctranscription” has been published online in Journal of Experimental Botany (DOI: 10.1093/jxb/erv459).

 

Dr. SHU Kai, associate professor of Sichuan Agricultural University, and CHEN Qian, Ph. D student of IGDB are the co-first authors. This work was supported by grants from The Ministry of Science and Technology of China and the National Natural Science Foundation of China.

 

Figure. A proposed working model in which ABA inhibits floral transition through activating FLC transcription by ABI4 and ABI5. (Image by IGDB)