State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, The Innovative Academy of Seed Design, Chinese Academy of Sciences, Beijing 100101, P. R. China.
State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, The Innovative Academy of Seed Design, Chinese Academy of Sciences, Beijing 100101, P. R. China; University of the Chinese Academy of Sciences, Beijing 100049, P. R. China.
Mol Plant. 2020 Nov 2;13(11):1556-1569. doi: 10.1016/j.molp.2020.09.008. Epub 2020 Sep 9.
A myriad of abiotic stress responses in plants are controlled by abscisic acid (ABA) signaling. ABA receptors can be degraded by both the 26S proteasome pathway and vacuolar degradation pathway after processing via the endosomal sorting complex required for transport (ESCRT) proteins. Despite being essential for ABA signaling, the upstream regulators of ESCRTs remain unknown. Here, we report that the ESCRT-I component VPS23A is an unstable protein that is degraded via the ubiquitin-proteasome system (UPS). The UEV domain of VPS23A physically interacts with the two PSAP motifs of XBAT35, an E3 ubiquitin ligase, and this interaction results in the deposition of K48 polyubiquitin chains on VPS23A, marking it for degradation by 26S proteasomes. We showed that XBAT35 in plants is a positive regulator of ABA responses that acts via the VPS23A/PYL4 complex, specifically by accelerating VPS23A turnover and thereby increasing accumulation of the ABA receptor PYL4. This work deciphers how an ESCRT component is regulated in plants and deepens our understanding of plant stress responses by illustrating a mechanism whereby crosstalk between the UPS and endosome-vacuole-mediated degradation pathways controls ABA signaling.
植物中有许多非生物胁迫反应受脱落酸（ABA）信号的控制。ABA 受体在经过内体分选复合物必需的运输（ESCRT）蛋白加工后，可以通过 26S 蛋白酶体途径和液泡降解途径降解。尽管 ESCRTs 对 ABA 信号至关重要，但 ESCRTs 的上游调节剂仍不清楚。在这里，我们报告说 ESCRT-I 成分 VPS23A 是一种不稳定的蛋白质，可通过泛素-蛋白酶体系统（UPS）降解。VPS23A 的 UEV 结构域与 XBAT35 的两个 PSAP 基序相互作用，XBAT35 是一种 E3 泛素连接酶，这种相互作用导致 VPS23A 上沉积 K48 多聚泛素链，使其被 26S 蛋白酶体降解。我们表明，植物中的 XBAT35 是 ABA 反应的正向调节剂，通过 VPS23A/PYL4 复合物发挥作用，特别是通过加速 VPS23A 的周转，从而增加 ABA 受体 PYL4 的积累。这项工作揭示了植物中 ESCRT 成分是如何被调控的，并通过阐明 UPS 和内体-液泡介导的降解途径之间的串扰如何控制 ABA 信号的机制，加深了我们对植物应激反应的理解。
