The Botrytis cinerea Crh1 transglycosylase is a cytoplasmic effector triggering plant cell death and defense response

Kai Bi,Amir Sharon,Javier Arroyo,Wenjun Zhu,Loredana Scalschi,Gal Masrati,Renana Fried,Ana Belén Sanz,Namrata Jaiswal,Tesfaye Mengiste

doi:10.1038/s41467-021-22436-1

Abstract

Crh proteins catalyze crosslinking of chitin and glucan polymers in fungal cell walls. Here, we show that the BcCrh1 protein from the phytopathogenic fungus Botrytis cinerea acts as a cytoplasmic effector and elicitor of plant defense. BcCrh1 is localized in vacuoles and the endoplasmic reticulum during saprophytic growth. However, upon plant infection, the protein accumulates in infection cushions; it is then secreted to the apoplast and translocated into plant cells, where it induces cell death and defense responses. Two regions of 53 and 35 amino acids are sufficient for protein uptake and cell death induction, respectively. BcCrh1 mutant variants that are unable to dimerize lack transglycosylation activity, but are still able to induce plant cell death. Furthermore, Arabidopsis lines expressing the bccrh1 gene exhibit reduced sensitivity to B. cinerea, suggesting a potential use of the BcCrh1 protein in plant immunization against this necrotrophic pathogen.

Highlights

Crh proteins catalyze crosslinking of chitin and glucan polymers in fungal cell walls
The glycosyl hydrolases (GHs) necrosis-inducing proteins (NIPs) that have been characterized so far remain in the apoplast after secretion by the fungus, and their cell death-inducing activity is mediated by plant extracellular membrane components, commonly in an SOBIR-BAK1-depedent manner[5,12,13]
We found that BcCrh[1] forms dimers, which seem to be necessary for the transglycosylase activity, while the monomeric protein is sufficient for induction of necrosis

Summary

Introduction

Crh proteins catalyze crosslinking of chitin and glucan polymers in fungal cell walls. A working model derived from these findings predicts secretion of cell death-inducing factors during the early stage that promote the formation of patches of dead tissue, which serve as foci for the subsequent stages[4]. This model has been supported by the discovery of secreted proteins with cell death-inducing activity, which are collectively referred to as necrosis-inducing proteins (NIPs)[5]. The best-studied NIPs are a family of non-catalytic NIPs collectively named NEP or NELP/NLP (NEP-like proteins)[6,7] Proteins in this family induce hypersensitive-like cell death in a variety of dicotyledonous, but not monocotyledonous plants[8,9,10]. Our study reveals an unexpected role for Crh proteins as mediators of fungal-plant interaction, and provides details on their role in fungal cell wall biosynthesis

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Conclusion