Functional Analysis Of MaSte12 Gene, A STE-like Transcription Factor In Metarhizium Acridum

Insect pests cause major devastation of crops, herbages and forests in world each year. Chemical pesticides have been the mainstay of insect pest control for a long time and eventually resulted in "3R" problems. It has been attracting numerous researchers' attention to search for environmentally friendly alternative, biologically based forms of pest control. Entomopathogenic fungi are important regulatory factors in pest insect populations in nature. Thus, entomopathogenic fungi have been an important source of biopesticides for pest control. Metarhizium acridum has been applied widely to control locust and an as important model organism for studies of host-pathogen interaction. M. acridum can infect their hosts by direct penetration of the cuticle. During infection, formation of mature and functional appressorium, the infection structure, is a key stage to guarantee the successful invasion. However, Although the molecular mechanisms of appressorium formation and cuticle penetration are still less clear. In plant pathogenic fungi, appressorium formation and successful penetration are mainly controlled by a Ste12 transcription factor, which activated directed by pathogen mitogen-activated protein kinase(PMK1). Once activated, Ste12 protein can regulate numerous genes expression through a transcritional regulation manner. But there was no functional analysis of Ste12-like transcription factor in entomopathogenic fungi. Here M. acridum and Lousta migratoria manilensis were selected as research materials to characterize the function of M. acridum Ste12 gene and reveal the molecular mechanisms in appressorium formation and cuticle penetration mediate by MaSte12 using RNA-seq.Using M. acridum genome sequence information, we amplified the full lenth of MaSte12 cDNA, which encoding a protein contained 702 amino acids. Protein sequence alignment shows that MaSte12 p has the typical feature of Ste12-like protein in fungi: a STE domain and two Zn_C2H2 zinc finger domains. Growth, stress tolerance and pathogenesis characteristics of wide-type, MaSte12 knockout and complementation strains were analyzed. The results show that MaSte12 affect conidial germination, but does not affect conidiation and stress tolerance in M. acridum. MaSte12 affect fungal pathogenicity to locust mainly because of appressorium formation defective. RNA-seq shows that MaSte12 regulate surface signal recognition, signal transduction, hydrophobin expression, fatty acids metabolism, carbohydrate metabolism, cell wall remodeling enzyme expression as well as cuticle degrading enzymes expression.Overall, our data provide a theoretical basis to reveal the pathogenesis of entomopathogenic fungi, and a large number of genetic resources to improve the biocontrol potential of biopesticides.