Functional analysis and mode of action of phytotoxic Nep1-like proteins of Botrytis cinerea

Nep1-like proteins (NLPs) induce necrosis and ethylene production in dicotyledonous plants. Botrytis cinerea contains two genes encoding NLPs, named Bcnep1 and Bcnep2. The activity of both proteins as well as the expression and function of the genes was studied. The genes are differentially expressed during pathogenesis. Mutants in either the Bcnep1 or Bcnep2 gene were equally virulent as the wild type strain. Site-directed mutant proteins were expressed in tobacco by agroinfiltration. Mutations in a conserved motif, or in either of two N-terminal cysteine residues abolished necrosis-inducing activity. The contribution of the plant to necrosis-inducing activity of B. cinerea NLPs was investigated using Arabidopsis mutants, virus-induced gene silencing and pharmacological inhibitors. The necrosis-inducing activity of B. cinerea NLPs does not seem to require cellular processes or defense signalling pathways previously identified to be involved in pathogen-induced plant cell death.