FgFim, a key protein regulating resistance to the fungicide JS399-19, asexual and sexual development, stress responses and virulence in Fusarium graminearum

Summary Fimbrin is an actin-bundling protein found in intestinal microvilli, hair cell stereocilia and fibroblast filopodia. Its homologue Sac6p has been shown to play a critical role in endocytosis and diverse cellular processes in Saccharomyces cerevisiae. FgFim from the wheat scab pathogenic fungus Fusarium graminearum strain Y2021A, which is highly resistant to the fungicide JS399-19, was identified by screening a mutant library generated by HPH-HSV-tk cassette-mediated integration. The functions of FgFim were evaluated by constructing a deletion mutant of FgFim, designated ΔFgFim-15. The deletion mutant exhibited a reduced rate of mycelial growth, reduced conidiation, delayed conidium germination, irregularly shaped hyphae, a lack of sexual reproduction on autoclaved wheat kernels and a dramatic decrease in resistance to JS399-19. ΔFgFim-15 also exhibited increased sensitivity to diverse metal cations, to agents that induce osmotic stress and oxidative stress, and to agents that damage the cell membrane and cell wall. Pathogenicity assays showed that the virulence of the FgFim deletion mutant on flowering wheat heads was impaired, which was consistent with its reduced production of the toxin deoxynivalenol in host tissue. All of these defects were restored by genetic complementation of the mutant with the parental FgFim gene. Quantitative real-time polymerase chain reaction (PCR) assays showed that the basal expression of three Cyp51 genes, which encode sterol 14α-demethylase, was significantly lower in the mutant than in the parental strain. The results of this study indicate that FgFim plays a critical role in the regulation of resistance to JS399-19 and in various cellular processes in F. graminearum.