P-153 - Structural and functional characterization of the fungal Ecp2 effector family.

Effectors play pivotal roles in disease development. Our research focuses on deciphering the biology of core effector proteins, including their intrinsic functions, contribution to virulence, and the molecular basis for their broad recognition by plant immune receptors. Here, we present a comprehensive structural, biochemical, and functional analysis of the Ecp2 core effector family in fungi, whose founding member was initially identified in the tomato pathogen Cladosporium fulvum. We have previously shown that CfEcp2 belongs to a novel, widely distributed multigene superfamily within the fungal kingdom, which we named Hce2 (Homologs of C. fulvum Ecp2). We also shown that most fungal species possess multiple Hce2 paralogs, some of which are fused to fungal Glycoside Hydrolase family 18 (GH18) chitinases with similarity to yeast Zymocin killer toxins. The crystal structure of CfEcp2 was solved to 2.09Å and shows a globular protein that multimerizes into a channel-like superstructure. CfEcp2 has highest structural homology to yeast killer toxins and other antimicrobial proteins, but despite these structural similarities, bioassays failed to demonstrate antimicrobial activity for CfEcp2. Instead, protein localization assays revealed that CfEcp2 interacts with the fungal cell wall by binding to specific carbohydrate components, a finding that was further supported by additional bioassays that highlighted the importance of this interaction and the role of CfEcp2 in the virulence.