Nuclear Activity of MLA Immune Receptors Links Isolate-Specific and Basal Disease-Resistance Responses

TLDR

Plant immune responses are initiated by pattern recognition receptors detecting conserved pathogen‑associated molecular patterns or by resistance proteins recognizing isolate‑specific pathogen effectors. In barley, nuclear‑localized MLA R proteins recognize the A10 effector, recruit WRKY transcription factors, and counteract their repression of PAMP‑triggered basal defense, thereby integrating isolate‑specific and basal disease‑resistance signals.

Abstract

Plant immune responses are triggered by pattern recognition receptors that detect conserved pathogen-associated molecular patterns (PAMPs) or by resistance (R) proteins recognizing isolate-specific pathogen effectors. We show that in barley, intracellular mildew A (MLA) R proteins function in the nucleus to confer resistance against the powdery mildew fungus. Recognition of the fungal avirulence A10 effector by MLA10 induces nuclear associations between receptor and WRKY transcription factors. The identified WRKY proteins act as repressors of PAMP-triggered basal defense. MLA appears to interfere with the WRKY repressor function, thereby de-repressing PAMP-triggered basal defense. Our findings reveal a mechanism by which these polymorphic immune receptors integrate distinct pathogen signals.