A small cysteine-rich protein from two kingdoms of microbes is recognized as a novel pathogen-associated molecular pattern.

Pathogen-associated molecular patterns (PAMPs) are conserved molecules which are crucial for normal life cycle of microorganisms. However, the diversity of microbial PAMPs is little known. During screening of cell death-inducing factors from the necrotrophic fungus Valsa mali, we identified a novel PAMP VmE02 that is widely spread in oomycetes and fungi. Agrobacterium tumefaciens-mediated transient expression or infiltration of recombinant protein produced by Escherichia coli was performed to assay elicitor activity of tested proteins. Virus-induced gene silencing (VIGS) in Nicotiana benthamiana was used to determine the components involved in VmE02-triggered cell death. The role of VmE02 in virulence and conidiation of V. mali were characterized by gene deletion and complementation. We found that, VmE02, together with some of its homologs from both oomycete and fungal species exhibited cell death-inducing activity in N. benthamiana. VmE02-triggered cell death was shown to be dependent on BRI1-ASSOCIATED KINASE-1 (BAK1), SUPPRESSOR OF BIR1-1 (SOBIR1), HSP90 and SGT1 in N. benthamiana. Deletion of VmE02 in V. mali greatly attenuated pathogen conidiation but not virulence, and treatment of N. benthamiana with VmE02 enhances plant resistance to Sclerotinia sclerotiorum and Phytophthora capsici. We conclude that VmE02 is a novel cross-kingdom PAMP produced by several fungi and oomycetes. This article is protected by copyright. All rights reserved.