College of Biological Sciences, China Agricultural University, Beijing 100094, China.
J Exp Bot. 2012 Nov;63(18):6371-92. doi: 10.1093/jxb/ers293. Epub 2012 Oct 23.
Three evolutionarily closely related WRKY-domain transcription factors WRKY18, WRKY40, and WRKY60 in Arabidopsis were previously identified as negative abscisic acid (ABA) signalling regulators, of which WRKY40 regulates ABI4 and ABI5 expression, but it remains unclear whether and how the three transcription factors cooperate to regulate expression of ABI4 and ABI5. In the present experiments, it was shown that WRKY18 and WRKY60, like WRKY40, interact with the W-box in the promoters of ABI4 and ABI5 genes, though the three WRKYs have their own preferential binding domains in the two promoters. WRKY18 and WRKY60, together with WRKY40, inhibit expression of the ABI5 and/or ABI4 genes, which is consistent with their negative roles in ABA signalling. Further, genetic evidence is provided that mutations of ABI4 and ABI5 genes suppress ABA-hypersensitive phenotypes of the null mutant alleles of WRKY18 and WRKY60 genes, demonstrating that ABI4 and ABI5 function downstream of these two WRKY transcription factors in ABA signalling. A working model of cooperation of the three WRKYs in repressing ABI4 and ABI5 expression is proposed, in which the three WRKYs antagonize or aid each other in a highly complex manner. These findings help to understand the complex mechanisms of WRKY-mediated ABA signal transduction.
先前在拟南芥中鉴定出三个进化上密切相关的 WRKY 结构域转录因子 WRKY18、WRKY40 和 WRKY60，它们是负向脱落酸（ABA）信号调节剂，其中 WRKY40 调节 ABI4 和 ABI5 的表达，但这三个转录因子是否以及如何合作来调节 ABI4 和 ABI5 的表达仍不清楚。在本实验中，表明 WRKY18 和 WRKY60 与 WRKY40 一样，与 ABI4 和 ABI5 基因启动子中的 W-box 相互作用，尽管这三个 WRKY 在两个启动子中有其自身的优先结合域。WRKY18 和 WRKY60 与 WRKY40 一起抑制 ABI5 和/或 ABI4 基因的表达，这与它们在 ABA 信号转导中的负调控作用一致。此外，遗传证据表明，ABI4 和 ABI5 基因的突变可抑制 WRKY18 和 WRKY60 基因缺失突变体的 ABA 超敏表型，表明 ABI4 和 ABI5 在 ABA 信号转导中作为这两个 WRKY 转录因子的下游发挥作用。提出了这三个 WRKY 协同抑制 ABI4 和 ABI5 表达的工作模型，其中三个 WRKY 以高度复杂的方式相互拮抗或相互帮助。这些发现有助于理解 WRKY 介导的 ABA 信号转导的复杂机制。
