Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.
Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada.
Plant J. 2022 May;110(4):961-977. doi: 10.1111/tpj.15713. Epub 2022 Mar 21.
Water stress can severely impact plant growth, productivity and yield. Consequently, plants have evolved various strategies through which they can respond and adapt to their environment. XERICO (XER) is a stress-responsive RING E3 ubiquitin ligase that modulates abscisic acid (ABA) levels and promotes drought tolerance when overexpressed. To better understand the biological role of XER in stress responses, we characterized a xer-1 hypomorphic mutant and a CRISPR/Cas9-induced xer-2 null mutant in Arabidopsis. Both xer mutant alleles exhibited increased drought sensitivity, supporting the results from overexpression studies. Furthermore, we discovered that both xer mutants have greater stomatal indices and that XER is expressed in epidermal cells, indicating that XER functions in the epidermis to repress stomatal development. To explore XER spatiotemporal and stress-dependent regulation, we conducted a yeast one-hybrid screen and found that CBF4/DREB1D associates with the XER 5' untranslated region (5'-UTR). We generated three cbf4 null mutants with CRISPR/Cas9 and showed that CBF4 negatively regulates ABA responses, promotes stomatal development and reduces drought tolerance, in contrast to the roles shown for XER. CBF4 is induced by ABA and osmotic stress, and localizes to the nucleus where it downregulates XER expression via the DRE element in its 5'-UTR. Lastly, genetic interaction studies confirmed that xer is epistatic to cbf4 in stomatal development and in ABA, osmotic and drought stress responses. We propose that the repression of XER by CBF4 functions to attenuate ABA signaling and stress responses to maintain a balance between plant growth and survival under adverse environmental conditions.
水分胁迫会严重影响植物的生长、生产力和产量。因此，植物已经进化出各种策略来应对和适应环境。XERICO（XER）是一种应激反应的 RING E3 泛素连接酶，当过度表达时，它可以调节脱落酸（ABA）的水平并促进耐旱性。为了更好地理解 XER 在应激反应中的生物学作用，我们对拟南芥中的 xer-1 弱等位基因和 CRISPR/Cas9 诱导的 xer-2 缺失突变体进行了表征。xer 突变体等位基因都表现出对干旱的敏感性增加，这支持了过表达研究的结果。此外，我们发现，两个 xer 突变体的气孔指数都更大，并且 XER 在表皮细胞中表达，这表明 XER 在表皮中起作用以抑制气孔发育。为了探索 XER 的时空和应激依赖性调节，我们进行了酵母单杂交筛选，发现 CBF4/DREB1D 与 XER 的 5'非翻译区（5'-UTR）结合。我们利用 CRISPR/Cas9 生成了三个 cbf4 缺失突变体，并表明 CBF4 负调控 ABA 反应，促进气孔发育并降低耐旱性，这与 XER 所表现出的作用相反。CBF4 被 ABA 和渗透胁迫诱导，并定位于核内，通过其 5'-UTR 中的 DRE 元件下调 XER 的表达。最后，遗传相互作用研究证实，在气孔发育和 ABA、渗透和干旱胁迫反应中，xer 对 cbf4 是上位的。我们提出，CBF4 对 XER 的抑制作用可减弱 ABA 信号和应激反应，以在不利的环境条件下维持植物生长和存活之间的平衡。
