The chitin synthase FgChs2 and other FgChss co-regulate vegetative development and virulence in F. graminearum

Fusarium graminearum contains eight chitin synthase (Chs) genes belonging to seven classes. Previous studies have found that deletion of FgChs3b is lethal to F. graminearum, and deletion of FgChs1, FgChs2, FgChs7 and FgChs5 caused diverse defects in chitin content, mycelial growth, conidiation, virulence or stress responses. However, little is known about the functional relationships among these FgChss. In this study, FgChs2 deletion mutant ΔFgChs2 exhibited reduced mycelial growth and virulence as reported previously. In addition, we found that the mutant produced thickened and "wavy" septa. Quantitative real-time PCR (qRT-PCR) assays showed that the expression levels of FgChs1, FgChs3a, FgChs4, FgChs7, FgChs5 and FgChs6 in ΔFgChs2 were significantly higher than those in the wild type. Therefore, we generated six double deletion mutants of FgChs2 and each of the above six FgChss, and found that FgChs2 shares a function with FgChs1 in regulating mycelial growth, and co-regulates conidiation with FgChs1, FgChs4, FgChs7 and FgChs5. Furthermore, FgChs2 and other six FgChss have overlapped functions in virulence, DON production and septum formation. Taken together, these results indicate that although each chitin synthase of F. graminearum plays certain roles, FgChss may co-regualte various cellular processes in F. graminearum.