Endocytosis in Fusarium graminearum requires coordination of the motor domain and two tail homology domains of myosin-1.

Fusarium graminearum is a major pathogen for the outbreak of Fusarium head blight disease. Recently, it was found that phenamacril (a Fusarium-specific fungicide) specifically inhibits the motor function of F. graminearum myosin-1 (FgMyo1). By using the FgMyo1-specific inhibitor phenamacril and genetic manipulation of FgMyo1 gene, we investigated the roles of each FgMyo1 domains (motor domain, TH1 domain, TH2 domain, SH3 domain, and CA domains) in supporting F. graminearum growth, with a special focus on endocytosis and subapical localization of FgMyo1. We demonstrate that FgMyo1 (a truncated FgMyo1 containing the motor domain, IQ motifs, TH1 and TH2 domains) is sufficient to support endocytosis of F. graminearum and subapical localization of FgMyo1. Biochemical analysis and electron microscopy revealed that FgMyo1 contains two actin-binding sites (the motor domain and the TH2 domain) and is able to crosslink actin filaments to form bundles. Based on above results, we propose a positive-feedback model explaining FgMyo1-dependent actin polymerization at endocytic site in subapical hyphae of F. graminearum: FgMyo1 molecules anchor at bottom of endocytic pitch, driving inward movement of actin filaments and enhancing actin polymerization; with more actin filaments are formed, more FgMyo1 molecules are recruited to the endocytic site.