Ubiquitin ligases in plant immunity: structural mechanisms and signaling

The ubiquitin system plays a central role in regulating plant growth, development, and immune responses. Within this system, E3 ubiquitin ligases act as key specificity factors that direct the modification and degradation of immune receptors, transcription factors, kinases, and hormone regulators. Recent advances reveal how diverse E3 ligase families, including Cullin–RING ligases (CRLs), RING-type, U-box, and RBR-type ligases, modulate both pattern-triggered and effector-triggered immunity. This review integrates new mechanistic and structural insights that clarify how E3s recognize substrates, assemble with E2 enzymes, and interface with pathogen effectors. Together, these studies uncover conserved catalytic principles and indicate pathogen-driven diversification of ubiquitin signaling. Emerging themes include feedback regulation, E3–E3 antagonism, and crosstalk with hormone pathways that balance defense and growth. Collectively, these findings redefine the ubiquitin–proteasome system as a dynamic regulatory network integrating perception, signaling, and proteostasis during plant immunity, offering new conceptual and practical avenues for enhancing disease resistance.