Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
Gene Discovery Research Group, RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa 230-0045, Japan.
Nat Plants. 2017 Jan 6;3:16204. doi: 10.1038/nplants.2016.204.
Rapid changes in messenger RNA population are vital for plants to properly exert multiple adaptive responses under continuously changing stress conditions. Transcriptional activation mediated by the 'abscisic acid (ABA)-activated SnRK2 protein kinases-ABA-responsive element (ABRE)-binding proteins/ABRE-binding factors (AREB/ABFs)' signalling module is a crucial step in the expression of stress-inducible genes under osmotic stress conditions in Arabidopsis. In addition to transcriptional control, proper transcript levels of individual genes can be achieved by post-transcriptional regulation, but how this regulation functions under stress conditions and the underlying molecular mechanisms remain elusive. Here, we show that ABA-unresponsive osmotic stress-activated subclass I SnRK2s and their downstream substrate, VARICOSE (VCS), an mRNA decapping activator, regulate mRNA decay under osmotic stress conditions. The expression of many stress-responsive genes was similarly misregulated in a mutant lacking all functional subclass I SnRK2s and in VCS-knockdown plants. Additionally, the mRNA decay of the transcripts of these genes was impaired in these plants under osmotic stress conditions. Furthermore, these plants showed growth retardation under osmotic stresses. Notably, subclass I-type SnRK2s have been identified in seed plants but not in lycophytes or mosses. Therefore, the post-transcriptional regulation mediated by the 'subclass I SnRK2s-VARICOSE' signalling module represents an additional mechanism of gene expression control that facilitates drastic changes in mRNA populations under osmotic stresses and might enhance the adaptability of seed plants to stress conditions.
信使 RNA 群体的快速变化对于植物在不断变化的胁迫条件下正确发挥多种适应性反应至关重要。在拟南芥的渗透胁迫条件下，“脱落酸（ABA）激活的 SnRK2 蛋白激酶-ABA 反应元件（ABRE）结合蛋白/ABRE 结合因子（AREB/ABFs）”信号模块介导的转录激活是胁迫诱导基因表达的关键步骤。除了转录控制外，个体基因的适当转录本水平可以通过转录后调控来实现，但这种调控在胁迫条件下如何发挥作用以及潜在的分子机制仍不清楚。在这里，我们表明 ABA 不响应渗透胁迫激活的 I 型 SnRK2 及其下游底物 VARICOSE（VCS），一种 mRNA 去帽激活因子，在渗透胁迫条件下调节 mRNA 衰变。许多应激响应基因的表达在缺乏所有功能性 I 型 SnRK2 和 VCS 敲低植物中也同样受到错误调控。此外，在这些植物中，这些基因的转录物的 mRNA 衰变在渗透胁迫条件下受损。此外，这些植物在渗透胁迫下表现出生长迟缓。值得注意的是，I 型 SnRK2 已在种子植物中被鉴定出来，但在石松类植物或苔藓植物中没有被鉴定出来。因此，由“I 型 SnRK2-VARICOSE”信号模块介导的转录后调控代表了一种额外的基因表达调控机制，它促进了在渗透胁迫下 mRNA 群体的剧烈变化，并且可能增强了种子植物对胁迫条件的适应性。
