Plant immune homeostasis is achieved through a balanced immune activation and suppression, enabling effective defense while averting autoimmunity. In Arabidopsis, disrupting a mitogen-activated protein (MAP) kinase cascade triggers nucleotide-binding leucine-rich-repeat (NLR) SUPPRESSOR OF mkk1/2 2 (SUMM2)-mediated autoimmunity. Through an RNAi screen, we identify PUB5, a putative plant U-box E3 ligase, as a critical regulator of SUMM2-mediated autoimmunity. In contrast to typical E3 ligases, PUB5 stabilizes CRCK3, a calmodulin-binding receptor-like cytoplasmic kinase involved in SUMM2 activation. A closely related E3 ligase, PUB44, functions oppositely with PUB5 to degrade CRCK3 through monoubiquitylation and internalization. Furthermore, CRCK3, highly expressed in roots and conserved across plant species, confers resistance to Fusarium oxysporum, a devastating soil-borne fungal pathogen, in both Arabidopsis and cotton. These findings demonstrate the antagonistic role of an E3 ligase pair in fine-tuning kinase proteostasis for the regulation of NLR-mediated autoimmunity and highlight the function of autoimmune activators in governing plant root immunity against fungal pathogens.

植物免疫稳态是通过平衡的免疫激活和抑制来实现的，从而在避免自身免疫的同时实现有效防御。在拟南芥中，破坏丝裂原激活蛋白 (MAP) 激酶级联会触发核苷酸结合富含亮氨酸重复序列 (NLR) 的mkk1/2 2 (SUMM2) 介导的自身免疫抑制剂。通过 RNAi 筛选，我们确定 PUB5（一种假定的植物 U-box E3 连接酶）是 SUMM2 介导的自身免疫的关键调节因子。与典型的 E3 连接酶相反，PUB5 可以稳定 CRCK3，这是一种参与 SUMM2 激活的钙调蛋白结合受体样细胞质激酶。密切相关的 E3 连接酶 PUB44 与 PUB5 功能相反，通过单泛素化和内化来降解 CRCK3。此外，CRCK3 在根部高度表达并在植物物种中保守，赋予拟南芥和棉花对尖孢镰刀菌（一种毁灭性土传真菌病原体）的抗性。这些发现证明了 E3 连接酶对在微调激酶蛋白稳态以调节 NLR 介导的自身免疫中的拮抗作用，并强调了自身免疫激活剂在控制植物根部针对真菌病原体的免疫中的功能。