Function Analysis Of MaSom1,a Transcription Factor,in Metarhizium Acridum

Metarhizium acridum is an important entomopathogenic fungus,so it is necessary to elucidate the molecular mechanism of infection.Flo8/Som1,which functions downstream from the cyclic AMP?cAMP?-dependent protein kinase A?PKA?pathway,plays important roles in hyphal development,spore formation and virulence in yeast and several filamentous fungi.However,the functions of Som1 in entomopathogenic fungi are still a mystery.In this study,MaSom1,a Flo8/Som1 homologue,was identified and functionally characterized in a model entomopathogenic fungus M.acridum in its spore production,stress resistance and infection.The main results are as follows:1.Similar to Flo8/Som1 in other fungi,MaSom1 mainly localized to the nucleus in M.acridum.2.Disruption of MaSom1 reduced conidial yield and delayed conidial germination.The half germination time(GT₅₀)was delayed,and the sporulation was reduced nearly to 40%of WT.3.Disruption of MaSom1 impaired the fungal tolerances to heat and UV-B.4.MaSom1 is also important for cell wall integrity and conidial surface structures in M.acridum.In?MaSom1,some genes related to fungal cell wall synthesis were down regulated,and the distribution of?-1,3-glucan on the surface of cell wall is increased,the?-1,3-glucans of conidia appeared to coagulate into a particle form and the coloring rate of chitin is about 1.88 times of WT.5.Bioassays showed that?MaSom1 had a dramatically decreased virulence after both topical inoculation and intrahemocoel injection of the fungus in locusts.6.Inactivation of MaSom1 diminished fungal growth in locust haemolymph in vitro and affected the penetration of M.anisopliae to the locust surface,delayed the conidial germination and reduced the formation of appressorium to 45.7%of WT on the locust hind wings.7.Inactivation of MaSom1 enhanced insect immune responses,the immune genes relate to Toll pathway are up-regulated,the extracellular phenoloxidase?PO?activity and the number of nodules in inner body wall are increased.Taken together,these results indicate that disruption of MaSom1 leads to a decline of fungal virulence because of impairments in conidial germination and appressorium formation,reduction of fungal growth in host haemolymph and enhancement of insect immune responses owing to the changes in conidial surface structures.In addition,the deletion of MaSom1 also impaired the fungal tolerances to heat and UV-B stres.