Fusarium sacchari is a causal agent of sugarcane Pokkah boeng, an important fungal disease that causes a considerable reduction in yield and sugar content in susceptible varieties of sugarcane worldwide. Despite its importance, the fungal factors that regulate the virulence of this pathogen remain largely unknown. In our previous study, mapping of an insertional mutant defect in virulence resulted in the identification of a cutinase G-box binding protein gene, designated FsCGBP, that encodes a C2H2-type transcription factor (TF). FsCGBP was shown to localize in the nuclei, and the transcript level of FsCGBP was significantly upregulated during the infection process or in response to abiotic stresses. Deletion or silencing of FsCGBP resulted in a reduction in mycelial growth, conidial production, and virulence and a delay in conidial germination in the F. sacchari. Cutinase genes FsCUT2, FsCUT3, and FsCUT4 and the mitogen-activated protein kinase (MAPK) genes FsHOG1, FsMGV1, and FsGPMK1, which were significantly downregulated in ΔFsCGBP. Except for FsHOG1, all of these genes were found to be transcriptionally activated by FsCGBP using the yeast one-hybrid system in vitro. The deletion of individual cutinase genes did not result in any of the phenotypes exhibited in the ΔFsCGBP mutant, except for cutinase activity. However, disruption of the MAPK pathway upon deletion of FsMGV1 or FsGPMK1 resulted in phenotypes similar to those of the ΔFsCGBP mutant. The above results suggest that FsCGBP functions by regulating the MAPK pathway and cutinase genes, providing new insights into the mechanism of virulence regulation in F. sacchari.
Keywords: C2H2 transcription factor; FsCGBP; Fusarium sacchari; MAPK pathway; sugarcane Pokkah boeng; virulence.