Understanding and manipulating the recognition of necrosis-inducing secreted protein 1 (NIS1) by BRI1-associated receptor kinase 1 (BAK1)

Necrosis-inducing secreted protein 1 (NIS1) is a core effector of Ascomycota and Basidiomycota fungi. They inhibit the immune responses of host plants mainly through interaction with the multi-functional coreceptor BRI1-associated receptor kinase 1 (BAK1). However, the structural mechanism of the NIS1 family and how they are recognized by BAK1 are unknown. Herein, we report the first crystal structure of the NIS1 family protein, the Magnaporthe oryzae NIS1 (MoNIS1), analyze the recognition mechanism of NIS1s by BAK1, and explore regulation of the NIS1-BAK1 interaction by a chemical compound. MoNIS1 exists as a β barrel formed by eight β strands, a folding mode that has not been reported. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) assay suggested that β4-β5 loop and β5 strand of MoNIS1 participate in OsBAK1 interaction, which was supported by further single-point mutational assays. For OsBAK1, HDX-MS assay suggested four regions involved in MoNIS1 interaction. Additionally, we identified a compound that blocks MoNIS1-OsBAK1 interaction in vitro and inhibits the virulence of M. oryzae on rice. Collectively, we determined the first structure of NIS1 family effectors, presented the recognition mechanism of NIS1 by BAK1, and showed that blocking NIS1-BAK1 interaction could be a new target for fungicide development.