Lysin Motif–Containing Proteins LYP4 and LYP6 Play Dual Roles in Peptidoglycan and Chitin Perception in Rice Innate Immunity

TLDR

Plant innate immunity depends on detecting microbial MAMPs through pattern‑recognition receptors on the cell surface. The study identifies rice LYP4 and LYP6 as dual‑function pattern‑recognition receptors that detect both bacterial peptidoglycan and fungal chitin. LYP4 and LYP6 localize to the plasma membrane, are rapidly induced by pathogens or MAMPs, bind peptidoglycan and chitin but not LPS, and their silencing selectively disrupts PGN‑ or chitin‑triggered defense responses—compromising resistance to Xanthomonas oryzae and Magnaporthe oryzae—while cross‑pre‑treatment with one MAMP dampens the response to the other, indicating overlapping perception components.

Abstract

Plant innate immunity relies on successful detection of microbe-associated molecular patterns (MAMPs) of invading microbes via pattern recognition receptors (PRRs) at the plant cell surface. Here, we report two homologous rice (Oryza sativa) lysin motif–containing proteins, LYP4 and LYP6, as dual functional PRRs sensing bacterial peptidoglycan (PGN) and fungal chitin. Live cell imaging and microsomal fractionation consistently revealed the plasma membrane localization of these proteins in rice cells. Transcription of these two genes could be induced rapidly upon exposure to bacterial pathogens or diverse MAMPs. Both proteins selectively bound PGN and chitin but not lipopolysaccharide (LPS) in vitro. Accordingly, silencing of either LYP specifically impaired PGN- or chitin- but not LPS-induced defense responses in rice, including reactive oxygen species generation, defense gene activation, and callose deposition, leading to compromised resistance against bacterial pathogen Xanthomonas oryzae and fungal pathogen Magnaporthe oryzae. Interestingly, pretreatment with excess PGN dramatically attenuated the alkalinization response of rice cells to chitin but not to flagellin; vice versa, pretreatment with chitin attenuated the response to PGN, suggesting that PGN and chitin engage overlapping perception components in rice. Collectively, our data support the notion that LYP4 and LYP6 are promiscuous PRRs for PGN and chitin in rice innate immunity.