The homeobox gene MaH1 governs microcycle conidiation for increased conidial yield by mediating transcription of conidiation pattern shift-related genes in Metarhizium acridum.

Conidiation capacity and conidial quality are very important for the production and application of mycopesticides. Most filamentous ascomycetous fungi have two distinct patterns of conidiation. Conidiation through microcycle conidiation proceeds to more rapidly achieve a maximum of conidial yield than normal conidiation and hence is of greater merit for exploitation in mass production of fungal insect pathogens, such as Metarhizium acridum. In this study, the mechanism underlying the conidiation pattern shift in M. acridum was explored by characterization of the fungal homeobox gene MaH1. MaH1 was evidently localized to the nuclei of hyphae and transcriptionally expressed at a maximal level when conidiation began. Intriguingly, deletion of MaH1 in M. acridum resulted in a shift of normal conidiation to microcycle conidiation on one-quarter strength Sabouraud's dextrose agar medium, and hence accelerated conidiation and increased conidial yield. In the deletion mutant, moreover, conidia became larger in size and hyphae cells were shorter in length while conidial virulence and stress tolerance were not altered. As revealed by digital gene expression profiling, MaH1 controlled the shift of conidiation patterns by mediating transcription of a set of genes related to hyphal growth, cell differentiation, conidiation, and some important signaling pathways. These findings indicate that MaH1 and its downstream genes can be exploited to increase the conidial yield for more efficient production of mycopesticides.