Redundant and distinct roles of two 14-3-3 proteins in Fusarium sacchari, pathogen of sugarcane Pokkah boeng disease

Fusarium sacchari is one of the most important sugarcane pathogens that causes Pokkah boeng disease (PBD) in China. 14-3-3 proteins have been shown to play vital roles in developmental processes in dimorphic transition, signal transduction and carbon metabolism in some phytopathogenic fungi, but were poorly understood in F. sacchari. In this study, two 14-3-3 protein-encoding genes, FsBmh1 and FsBmh2 in F. sacchari, were investigated. Although both FsBmh1 and FsBmh2 were expressed at vegetative growth stage, FsBmh1 was repressed at sporulation stage in vitro. In order to clarify the roles of FsBmh1 and FsBmh2, deletion mutants {Delta}FsBmh1 and {Delta}FsBmh2 were constructed. Phenotypic defects, including hyphal branching, hyphal septation, conidiation, spore germination and colony growth, were more severe in {Delta}FsBmh2 than in {Delta}FsBmh1, although virulence attenuation was observed in both mutants. To further explore the relationship between FsBmh1 and FsBmh2, the combination of deletion and silencing ({Delta}FsBmh/sFsBmh) and overexpression (O-FsBmh) mutants were constructed and characterized. Compared to the single allele deletion, combinations of {Delta}FsBmh1/sFsBmh2 or {Delta}FsBmh2/sFsBmh1 showed more severe manifestations in general, suggesting a redundancy in function of the two 14-3-3 genes. Comparative transcriptome analysis revealed that more functional genes were affected in {Delta}FsBmh2 than in {Delta}FsBmh1. Redundancy in function between FsBmh1 and FsBmh2 suggests that 14-3-3 is vitally important for the organism and distinction in roles between the two isoforms may be resulted from the divergence in evolution. To the best of our knowledge, this was the first report on the distinct roles of 14-3-3 protein isoforms in a pathogenic fungus. Knowledge gained from this study should be of help to further understand the regulation mechanism of pathogenicity-related traits in fungal pathogens and for the development of new strategy for control of PBD in particular.