RLP23 is required for Arabidopsis immunity against the grey mould pathogen Botrytis cinerea

Necrosis- and ethylene-inducing-like proteins (NLPs) are secreted by fungi, oomycetes and bacteria. Conserved nlp peptides derived from NLPs are recognized as pathogen-associated molecular patterns (PAMPs), leading to PAMP-triggered immune responses. RLP23 is the receptor of the nlp peptides in Arabidopsis thaliana; however, its actual contribution to plant immunity is unclear. Here, we report that RLP23 is required for Arabidopsis immunity against the necrotrophic fungal pathogen Botrytis cinerea. Arabidopsis rlp23 mutants exhibited enhanced susceptibility to B. cinerea compared with the wild-type plants. Notably, microscopic observation of the B. cinerea infection behaviour indicated the involvement of RLP23 in pre-invasive resistance to the pathogen. B. cinerea carried two NLP genes, BcNEP1 and BcNEP2; BcNEP1 was expressed preferentially before/during invasion into Arabidopsis, whereas BcNEP2 was expressed at the late phase of infection. Importantly, the nlp peptides derived from both BcNEP1 and BcNEP2 induced the production of reactive oxygen species in an RLP23-dependent manner. In contrast, another necrotrophic fungus Alternaria brassicicola did not express the NLP gene in the early infection phase and exhibited no enhanced virulence in the rlp23 mutants. Collectively, these results strongly suggest that RLP23 contributes to Arabidopsis pre-invasive resistance to B. cinerea via NLP recognition at the early infection phase.