Mutation of a Nucleotide-Binding Leucine-Rich Repeat Immune Receptor-Type Protein Disrupts Immunity to Bacterial Blight

Most characterized plant resistance proteins belong to the nucleotide-binding domain and Leu-rich repeat-containing (NLR) family. NLRs are present in an auto-inhibited state in the absence of specific pathogens, while gain-of-function mutations in NLRs usually cause autoimmunity. Here, we show that a gain-of-function mutation, weaker defense ( wed ), which caused a Phe-to-Leu substitution in the nucleotide-binding domain of a typical NLR in rice ( Oryza sativa ), led to enhanced susceptibility to Xanthomonas oryzae pv. Oryzae The unexpected accumulation of salicylic acid (SA), along with downregulation of NONEXPRESSOR OF PR1 ( NPR1 ), in wed indicates the potential presence of a feedback regulation loop of SA biosynthesis in rice. Epistasis analyses illustrated that SA accumulation and the NLR-associated components RAR1, OsRac1, and PhyB are dispensable for the wed phenotypes. Intriguingly, besides pattern-triggered immunity, effector-triggered immunity conferred by different resistance proteins, including Xa3/Xa26, Xa4, and Xa21, was also disturbed by wed to a certain extent, indicating the existence of shared regulatory mechanisms for various defense systems. The identification of wed therefore provides a unique system for genetic dissection of shared immune signaling pathways activated by different types of immune receptors.