A coordinated, multi-subunit chitin deacetylase complex for robust evasion of wheat immunity by Fusarium graminearum

Fusarium head blight (FHB), caused by Fusarium graminearum, poses a significant threat to global wheat production. F. graminearum-mediated suppression of host immunity is critical for infection, yet the underlying mechanisms remain incompletely understood. Fungal chitin deacetylases (CDAs) are known to modify cell wall chitin, a potent microbe-associated molecular pattern, to evade plant defenses. Here, we investigated the CDA family in F. graminearum and identified four secreted paralogs, FgCDA1-4, that are highly induced during wheat infection. Functional analyses confirmed that all four are potent virulence factors, protecting fungal hyphae from degradation by host proteins and suppressing chitin-triggered immunity, including ROS production and callose deposition. Crucially, genetic analysis of single, double, and quadruple deletion mutants revealed a non-additive functional relationship; the virulence defect in multigene mutants was no greater than that of single-gene mutants, pointing to a coordinated mechanism rather than functional redundancy. We subsequently showed through yeast two-hybrid assays, co-immunoprecipitation, and AlphaFold-based structural modeling that FgCDA1-4 physically interact and are likely to assemble into hetero-oligomeric complexes. Our findings uncover a sophisticated immune evasion strategy where F. graminearum deploys a multi-subunit enzymatic complex to ensure robust virulence. This FgCDA complex represents a novel, high-value target for developing durable FHB resistance.