Rho4 interacts with BbGDI and is essential for the biocontrol potential of Beauveria bassiana by maintaining intracellular redox homeostasis

Rho4 is a member of the Rho-family small GTPases. In this study, we revealed the function of Rho4 and explored its mechanism involved in intracellular redox homeostasis in Beauveria bassiana, one of the most widely utilized filamentous entomopathogenic fungi. The disruption of Rho4 in B. bassiana resulted in significant phenotypic changes, such as fungal virulence, growth rate on different media, thermotolerance, germination, and conidiation. Integrated analysis of proteomic and transcriptomic data unveiled differential expression patterns of various redox-related genes and proteins in Δrho4, including the down-regulation of GST shown in proteomic and transcriptomic data, and the down-regulated gene expression levels of NOX, SOD, CAT, and GR in the transcriptome. Based on the bi-omics analysis, we focused on the impact of Rho4 in maintaining intracellular redox homeostasis. A decreased ROS content observed in Δrho4 might be attributed to the reduced NOX activity, which subsequently affects the GSH-producing/consuming metabolisms, with the attenuated activities of GR and GST. The imbalanced redox homeostasis also resulted in the reduced enzyme activities of SOD and CAT. Exogenous oxides could partially complement the ROS level and rescue the growth defect in Δrho4 to a certain extent. Besides, BbGDI was initially identified as an interacting protein of Rho4 in entomopathogenic fungi. Our results provide a comprehensive understanding of the function and regulating mechanism of Rho4 in B. bassiana.