Mr-AbaA Regulates Conidiation by Interacting with the Promoter Regions of Both Mr-veA and Mr-wetA in Metarhizium robertsii

Conidiation is a pivotal strategy for fungi to resist adverse environments and disperse to new habitats, which is especially important for entomopathogenic fungi whose conidia are infective as fungal pesticide propagules. However, the molecular mechanism for regulating conidiation in entomopathogenic fungi is not fully understood. Here, we characterized the regulatory mechanism of the key developmental transcription factor Mr-AbaA. Bioinformatic analysis, transcriptional profiles, and subcellular localization of Mr-abaA indicated that AbaA functioned as a transcription factor in the conidiophore development and conidium stages. Microscopic examination showed that the null mutant of Mr-abaA differentiated into defective phialides to produce an abacus structure instead of conidia. Loss of Mr-abaA resulted in the inhibition of submerged blastospore separation in vitro. Moreover, yeast (Saccharomyces cerevisiae) one-hybrid assays of interactions between genes and deletion of Mr-veA showed that Mr-AbaA regulates conidiation by interacting with the promoter regions of Mr-veA and Mr-wetA. These results demonstrate that Mr-AbaA positively regulates conidiation in Metarhizium robertsii by regulating the velvet family ortholog gene Mr-veA and contributes to the separation of blastospores in submerged culture. IMPORTANCE Metarhizium robertsii is an emerging model entomopathogenic fungus for developing biopesticides; therefore, a comprehensive understanding of its conidiation is very important for its application. In this study, we revealed that the transcription factor Mr-AbaA is involved in the control of aerial conidiation and blastospore separation in submerged culture. Further yeast one-hybrid assays demonstrated that Mr-AbaA interacts with the promoter regions of Mr-veA and Mr-wetA, which code for proteins involved in the control of conidiation. This finding provides new insight into the regulation of the conidiation of this important entomopathogenic fungi.