Transcription Factor Mavib-1 Negatively Regulates Conidiation by Affecting Utilization of Carbon and Nitrogen Source in Metarhizium acridum .

Conidium is the main infection unit and reproductive unit of pathogenic fungi. Exploring the mechanism of conidiation and its regulation contributes to understanding the pathogenicity of pathogenic fungi. Vib-1 , a transcription factor, was reported to participate in the conidiation process. However, the regulation mechanism of Vib-1 in conidiation is still unclear. In this study, we analyzed the function of Vib-1 and its regulation mechanism in conidiation through knocking out and overexpression of Vib-1 in entomopathogenic fungus Metarhizium acridum . Results showed that the colonial growth of Mavib-1 disruption mutant (Δ Mavib-1 ) was significantly decreased, and conidiation was earlier compared to wild type (WT), while overexpression of Mavib-1 led to a delayed conidiation especially when carbon or nitrogen sources were insufficient. Overexpression of Mavib-1 resulted in a conidiation pattern shift from microcycle conidiation to normal conidiation on nutrient-limited medium. These results indicated that Mavib-1 acted as a positive regulator in vegetative growth and a negative regulator in conidiation by affecting utilization of carbon and nitrogen sources in M. acridum . Transcription profile analysis demonstrated that many genes related to carbon and nitrogen source metabolisms were differentially expressed in Δ Mavib-1 and OE strains compared to WT. Moreover, Mavib-1 affects the conidial germination, tolerance to UV-B and heat stresses, cell wall integrity, conidial surface morphology and conidial hydrophobicity in M. acridum . These findings unravel the regulatory mechanism of Mavib-1 in fungal growth and conidiation, and enrich the knowledge to conidiation pattern shift of filamentous fungi.