LsGRP1, a class II glycine‐rich protein of Lilium, confers plant resistance via mediating innate immune activation and inducing fungal programmed cell death

Defence‐related LsGRP1 is a leaf‐specific plant class II glycine‐rich protein (GRP) involved in salicylic acid‐induced systemic resistance against grey mould caused by necrotrophic Botrytis elliptica in lily (Lilium) cultivar Stargazer. The C‐terminal region of LsGRP1 (LsGRP1(C)) can inhibit fungal growth in vitro via a mechanism of inducing fungal apoptosis programmed cell death (PCD). In this study, the role of LsGRP1 in induced defence mechanism was investigated using LsGRP1‐silenced Stargazer lily and LsGRP1‐transgenic Arabidopsis thaliana. LsGRP1 silencing in lily was found to slightly inhibit plant growth and greatly increase the susceptibility to B. elliptica by suppressing callose deposition and early reactive oxygen species (ROS) accumulation. In contrast, LsGRP1‐transgenic Arabidopsis showed higher resistance to Botrytis cinerea and also to Pseudomonas syringae pv. tomato DC3000 as compared to the wild type, accompanied with the enhancement of callose deposition and ROS accumulation. Additionally, LsGRP1 silencing increased plant cell death caused by B. elliptica secretion and reduced pathogen‐associated molecular pattern (PAMP)‐triggered defence activation in Stargazer lily. Consistently, LsGRP1 expression boosted PAMP‐triggered defence responses and effector recognition‐induced hypersensitive response in Arabidopsis. Moreover, fungal apoptosis PCD triggered by LsGRP1 in an LsGRP1(C)‐dependent manner was demonstrated by leaf infiltration with LsGRP1(C)‐containing recombinant proteins in Stargazer lily. Based on these results, we presume that LsGRP1 plays roles in plant defence via functioning as a pathogen‐inducible switch for plant innate immune activation and acting as a fungal apoptosis PCD inducer to combat pathogen attack.