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.

植物中无数的非生物胁迫反应是由脱落酸（ABA）信号控制的。通过运输（ESCRT）蛋白所需的内体分选复合物加工后，ABA受体可以通过26S蛋白酶体途径和液泡降解途径降解。尽管对于ABA信号传导至关重要，但ESCRT的上游调节子仍然未知。在这里，我们报告ESCRT-1组件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域与XBAT35的两个PSAP基序（E3泛素连接酶）发生物理相互作用，这种相互作用导致K48聚泛素链在VPS23A上沉积，从而使其被26S蛋白酶体降解。我们表明，植物中的XBAT35是ABA应答的正调节剂，它通过VPS23A / PYL4复合物起作用，特别是通过加速VPS23A转换并从而增加ABA受体PYL4的积累。这项工作解释了ESCRT成分在植物中的调控方式，并通过说明一种机制来加深我们对植物胁迫反应的理解，在该机制中，UPS与内体-真空介导的降解途径之间的串扰控制了ABA信号传导。