Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA.
J Exp Bot. 2013 Aug;64(11):3425-37. doi: 10.1093/jxb/ert179.
Rac-like GTPases or Rho-related GTPases from plants (RAC/ROPs) are important components of hormone signalling pathways in plants. Based on phylogeny, several groups can be distinguished, and the underlying premise is that members of different groups perform distinct functions in the plant. AtRAC7/ROP9 is phylogenetically unique among 11 Arabidopsis RAC/ROPs, and here it was shown that it functions as a modulator of auxin and abscisic acid (ABA) signalling, a dual role not previously assigned to these small GTPases. Plants with reduced levels of AtRAC7/ROP9 had increased sensitivity to auxin and were less sensitive to ABA. On the other hand, overexpressing AtRAC7/ROP9 activated ABA-induced gene expression but repressed auxin-induced gene expression. In addition, both hormones regulated the activity of the AtRAC7/ROP9 promoter, suggesting a feedback mechanism to modulate the signalling output from the AtRAC7/ROP9-controlled molecular switch. High levels of AtRAC7/ROP9 were detected specifically in embryos and lateral roots, underscoring the important role of this protein during embryo development and lateral root formation. These results place AtRAC7/ROP9 as an important signal transducer in recently described pathways that integrate auxin and ABA signalling in the plant.
植物中的 Rac 样 GTP 酶或 Rho 相关 GTP 酶（RAC/ROPs）是植物激素信号通路中的重要组成部分。基于系统发育，可区分出几个组，其基本前提是不同组的成员在植物中执行不同的功能。在拟南芥的 11 个 RAC/ROPs 中，AtRAC7/ROP9 在系统发育上是独特的，研究表明它作为生长素和脱落酸（ABA）信号的调节剂发挥作用，这是这些小 GTP 酶以前未被赋予的双重作用。AtRAC7/ROP9 水平降低的植物对生长素的敏感性增加，对 ABA 的敏感性降低。另一方面，过表达 AtRAC7/ROP9 会激活 ABA 诱导的基因表达，但抑制生长素诱导的基因表达。此外，这两种激素都调节 AtRAC7/ROP9 启动子的活性，表明存在一种反馈机制来调节由 AtRAC7/ROP9 控制的分子开关的信号输出。AtRAC7/ROP9 的高水平特异性地在胚胎和侧根中检测到，这强调了该蛋白在胚胎发育和侧根形成过程中的重要作用。这些结果将 AtRAC7/ROP9 置于最近描述的途径中的重要信号转导子，该途径整合了植物中的生长素和 ABA 信号。
