Functional Analysis Of Rho Family Proteins In Fusarium Graminearum

Wheat scab, caused by Fusarium graminearum, is one of the most important wheat diseases worldwide, yet the mechanisms associated with making this fungus such a devastating pathogen remain largely ambiguous. Rho GTPases have multiple cellular and metabolic functions, including vesicular trafficking and pathogenesis, as signaling molecules in fungi. We supposed that Rho GTPases may also involve in these processes in F. graminearum. Therefore, functional analysis of the FgRho proteins will contribute to uncover the physiological process and mechanism of pathogenesis.In an effort to better understand the function of F. graminearum, all six Rho GTPases in F. graminearum were functionally characterized by gene knockout method. FgRHO1 was determined to be essential for fungus survival, while FgRho3 only demonstrated functions in vegetative growth and conidiation. Other four Rho GTPases, FgRho2, FgRho4, FgCdc42 and FgRac1, were multifunctional and involved ir sexual development and pathogenesis. Besides playing roles in cell wall integrity as FgRho2, FgRho4 also involves in nuclear division and is essential for septum formation. While FgRho2 and FgRho4 are both involved in cell wall integrity, only FgRho4 shows a role in nuclear division and septum formation. FgRho4, FgCdc42 and FgRacl are also important in hyphal growth and conidiation. All single deletion mutants show impaired growth, particularly in conidial morphology, when compared to the wild-type progenitor. FgRacl deletion mutants display a precocious, multi-site germ tube formation as well as hyperbranching of hyphae. Significantly, we find that FgRac1 negatively controls DON production whereas FgRho4 plays a positive role.Moreover, FgCla4 and FgNoxR were identifed as downstream targets of FgRacl. FgRacl regulates vegetative growth and conidiation by interacting with FgCla4 while regulates female fertility by interacting with FgNoxR and FgNoxl. FgCla4 and FgNoxR are important for pathogenesis suggesting that FgRacl may regulate pathogenesis by these two targets in F. graminearum.In summay, FgRho GTPases play diversified roles in the life cycle of F. graminearm including four of them are involved in pathogenesis. In addition, FgRacl interacts with its two downstream targets, FgCla4 and FgNoxR, to regulate different processes.