French Associates Institute for Agriculture and Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, 84990, Israel.
Plant J. 2014 Jul;79(1):28-43. doi: 10.1111/tpj.12533. Epub 2014 May 27.
DEAD-box RNA helicases are involved in many aspects of RNA metabolism and in diverse biological processes in plants. Arabidopsis thaliana mutants of two DEAD-box RNA helicases, STRESS RESPONSE SUPPRESSOR1 (STRS1) and STRS2 were previously shown to exhibit tolerance to abiotic stresses and up-regulated stress-responsive gene expression. Here, we show that Arabidopsis STRS-overexpressing lines displayed a less tolerant phenotype and reduced expression of stress-induced genes confirming the STRSs as attenuators of Arabidopsis stress responses. GFP-STRS fusion proteins exhibited localization to the nucleolus, nucleoplasm and chromocenters and exhibited relocalization in response to abscisic acid (ABA) treatment and various stresses. This relocalization was reversed when stress treatments were removed. The STRS proteins displayed mis-localization in specific gene-silencing mutants and exhibited RNA-dependent ATPase and RNA-unwinding activities. In particular, STRS2 showed mis-localization in three out of four mutants of the RNA-directed DNA methylation (RdDM) pathway while STRS1 was mis-localized in the hd2c mutant that is defective in histone deacetylase activity. Furthermore, heterochromatic RdDM target loci displayed reduced DNA methylation and increased expression in the strs mutants. Taken together, our findings suggest that the STRS proteins are involved in epigenetic silencing of gene expression to bring about suppression of the Arabidopsis stress response.
DEAD-box RNA 解旋酶参与 RNA 代谢的多个方面，以及植物中的多种生物学过程。先前已经证明，拟南芥两种 DEAD-box RNA 解旋酶（STRS1 和 STRS2）的突变体对非生物胁迫具有耐受性，并上调胁迫响应基因的表达。在这里，我们发现拟南芥 STRS 过表达系表现出较低的耐受性表型和应激诱导基因表达的减少，证实 STRS 是拟南芥应激反应的衰减因子。GFP-STRS 融合蛋白定位于核仁、核质和染色质中心，并在响应脱落酸（ABA）处理和各种胁迫时发生重定位。当去除应激处理时，这种重定位会逆转。STRS 蛋白在特定基因沉默突变体中显示出错误定位，并表现出 RNA 依赖性 ATP 酶和 RNA 解链活性。特别是，STRS2 在 RNA 指导的 DNA 甲基化（RdDM）途径的四个突变体中的三个中显示出错误定位，而 STRS1 在组蛋白去乙酰化活性有缺陷的 hd2c 突变体中显示出错误定位。此外，异染色质 RdDM 靶标位点在 strs 突变体中显示出 DNA 甲基化减少和表达增加。总之，我们的研究结果表明，STRS 蛋白参与基因表达的表观遗传沉默，从而抑制拟南芥的应激反应。
