E3 ubiquitin ligases in plant defense: mechanisms and prospects for resistance breeding.

Biotic stress is a major constraint on global crop productivity and a persistent challenge to sustainable agriculture. The ubiquitin-proteasome system (UPS) serves as a central post-translational regulatory hub coordinating plant growth, stress adaptation, and immune responses. Within this system, E3 ubiquitin ligases confer substrate specificity by recognizing and ubiquitinating target proteins, thereby shaping immune signaling networks at multiple levels. Recent studies have revealed that plant E3 ligases regulate both pattern-triggered and effector-triggered immunity by controlling the stability of immune receptors, signaling intermediates, and transcriptional regulators, while also playing crucial roles in antiviral defense and resistance to herbivorous insects. In parallel, diverse pathogen effectors have evolved to target, hijack, or mimic host E3 ligases, illustrating an intense coevolutionary arms race centered on ubiquitin-mediated regulation. Building on these mechanistic insights, emerging research hotspots, including structural dissection of E3-substrate interactions, genome editing, promoter engineering, and allelic variation mining, are opening new avenues to fine-tune immunity while minimizing growth penalties. This review synthesizes current advances in E3 ligase-mediated plant defense, highlights pathogen strategies that exploit ubiquitination pathways, and discusses future perspectives for leveraging E3 ligases in resistance breeding and sustainable crop protection.