In plants, the ubiquitin-proteasome system, endosomal sorting, and autophagy are essential for protein degradation; however, their interplay remains poorly understood. Here, we show that four Arabidopsis (Arabidopsis thaliana) E3 ubiquitin ligases, SEVEN IN ABSENTIA OF ARABIDOPSIS THALIANA1 (SINAT1), SINAT2, SINAT3, and SINAT4, regulate the stabilities of FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING1 (FREE1) and VACUOLAR PROTEIN SORTING23A (VPS23A), key components of the endosomal sorting complex required for transport-I, to modulate abscisic acid (ABA) signaling. GFP-SINAT1, GFP-SINAT2, and GFP-SINAT4 primarily localized to the endosomal and autophagic vesicles. SINATs controlled FREE1 and VPS23A ubiquitination and proteasomal degradation. SINAT overexpressors showed increased ABA sensitivity, ABA-responsive gene expression, and PYRABACTIN RESISTANCE1-LIKE4 protein levels. Furthermore, the SINAT-FREE1/VPS23A proteins were codegraded by the vacuolar pathway. In particular, during recovery post-ABA exposure, SINATs formed homo- and hetero-oligomers in vivo, which were disrupted by the autophagy machinery. Taken together, our findings reveal a novel mechanism by which the proteasomal and vacuolar turnover systems regulate ABA signaling in plants.

在植物中，泛素-蛋白酶体系统、内体分选和自噬对于蛋白质降解至关重要。然而，它们的相互作用仍然知之甚少。在这里，我们展示了四种拟南芥 ( Arabidopsis thaliana ) E3 泛素连接酶，其中七个缺乏拟南芥 ( Arabidopsis thaliana)1 (SINAT1)、SINAT2、SINAT3 和 SINAT4，调节内体分选所需的 FYVE 结构域蛋白 1 (FREE1) 和空泡蛋白分选23A (VPS23A) 的稳定性，这是转运 I 所需的内体分选复合物的关键成分，以调节脱落酸 (ABA) 信号传导。GFP-SINAT1、GFP-SINAT2 和 GFP-SINAT4 主要定位于内体和自噬囊泡。SINAT 控制 FREE1 和 VPS23A 泛素化和蛋白酶体降解。SINAT 过表达者表现出 ABA 敏感性、ABA 响应基因表达和 PYRABACTIN RESISTANCE1-LIKE4 蛋白水平增加。此外，SINAT-FREE1/VPS23A 蛋白通过液泡途径进行共降解。特别是，在 ABA 暴露后的恢复过程中，SINAT 在体内形成同源和异源寡聚体，并被自噬机制破坏。综合起来，