TAF15b, involved in the autonomous pathway for flowering, represses transcription of FLOWERING LOCUS C

First author: Hyunjoo Eom; Affiliations: Seoul National University (国立首尔大学): Seoul, Korea

Corresponding author: Ilha Lee

TATA-binding protein-associated factors (TAFs) are general transcription factors within the transcription factor IID (TFIID) complex, which recognizes the core promoter of genes. In addition to their biochemical function, it is known that several TAFs are involved in the regulation of developmental processes. In this study, we found that TAF15b affects flowering time, especially through the autonomous pathway (AP; 自主途径) in Arabidopsis. The mutant taf15b shows late flowering compared with the wild type plant during both long and short days, and vernalization (春化) accelerates the flowering time of taf15b. In addition, taf15b shows strong upregulation of FLOWERING LOCUS C (FLC), a flowering repressor in Arabidopsis, and the flc taf15b double mutant completely offsets (抵消) the late flowering of taf15b, indicating that TAF15b is a typical AP gene. The taf15b mutant also shows increased transcript levels of COOLAIR, an antisense transcript (反义转录本) of FLC. Consistently, chromatin immunoprecipitation (ChIP) analyses showed that the TAF15b protein is enriched around both sense and antisense transcription start sites of the FLC locus. In addition, co-immunoprecipitation showed that TAF15b interacts with RNA polymerase II (Pol II), while ChIP showed increased enrichment of the phosphorylated (磷酸化) forms, both serine 2 (Ser2) and Ser5, of the C-terminal domain of Pol II at the FLC locus, which is indicative of transcriptional elongation (转录伸长). Finally, taf15b showed higher enrichment of the active histone marker, H3K4me3, on FLC chromatin. Taken together, our results suggest that TAF15b affects flowering time through transcriptional repression of FLC in Arabidopsis.

TATA结合蛋白相关因子TAF是转录因子IID复合物内的基本转录因子，作用是识别基因的核心启动子。除了TAF的生物生化作用，已知一些TAF会参与到发育进程的调控。本文发现TAF15b会影响拟南芥开花时间，尤其是通过自主途径。taf15b突变体与野生型相比会在长日照和短日照下都延迟开花，春化会加速taf15b开花。另外，taf15b突变体中拟南芥开花抑制基因FLC受到强烈上调，flc taf15b双突变体会完全抵消taf15b突变体的晚花表型，表明TAF15b是一个典型的自主途径基因。taf15b突变体同样还会增加FLC的一个翻译转录本COOLAIR基因的转录水平。同样，染色质免疫沉淀ChIP分析显示TAF15b蛋白在FLC正义和反义转录起始位点上富集。另外，免疫共沉淀显示TAF15b会与RNA聚合酶II互作，同时ChIP结果显示在FLC基因上Pol II的C端结构域Ser2和Ser5的磷酸化富集程度增加，显示转录的伸长。最终，taf15b显示活性组蛋白标记H3K4me3在FLC染色质上更高的富集程度。综上，本文的结果显示TAF15b会通过FLC的转录抑制影响拟南芥的开花时间。

通讯：Ilha Lee (http://biosci.snu.ac.kr/en/people/faculty?mode=view&profidx=31)

个人简介：1982.3 - 1986.2，学士；1986.3 - 1988.2，硕士；1990.6 - 1994.12，威斯康星大学麦迪逊分校，生物化学博士。

doi: 10.1111/tpj.13758