Functional Analysis Of The Two-component Histidine Kinase MaSln1 In Metarhizium Acridum

As an environmentally friendly biological insecticide,fungal insecticide has many advantages such as low likelihood to inducing insect resistance and sustainable control,thus exhibiting a great potential in biological control.However,the shortcomings such as high cost,slow speed to kill pests and susceptibility to environmental factors limit their large-scale application.Conidia are the main infection units of entomopathogenic fungi,thus the conidial yield and quality can surely affect the production cost and the control effect of fungal pesticides.Therefore,clarifying the regulation mechanism of the conidial yield and quality in entomopathogenic fungi,is widely expected to provide a theoretical basis for improving the production efficiency of fungal insecticides.Sln1,a conserved sensor kinase in the HOG-MAPK pathway,played different functions in different fungi.In this study,we found that the coding sequence of MaSln1 is 3426 bp,containing an intron of 60 bp,which encodes a protein of 1121 amino acids through bioinformatics analysis in the model entomopathogenic fungus M.acridum.The molecular mass and the isoelectric point are 122.8 k D and 6.88,respectively.The functions of MaSln1 were analyzed in M.acridum through gene knockout and rescue strategies.Results showed that deletion of MaSln1 did not affect the fungal germination rate,conidial yield as well as resistances to chemical agents.However,fungal tolerances to UV-B and wet-heat were significantly reduced after the deletion of MaSln1.Bioassays showed that the virulence was significantly reduced when MaSln1 was deleted.Further studies showed that MaSln1 affected neither germination nor appressorium formation of M.acridum on locust wings,but significantly increased the appressorium turgor pressure.In addition,we found that deletion of MaSln1 led to conidiation pattern shift of M.acridum on SYA medium.By observing the conidiation patterns of some other mutants in the MAPK pathway(ΔMaSho1,ΔMa Hog1,ΔMa Mk1 and ΔMaSlt2)on SYA medium,we speculated that the conidiation pattern shift in M.acridum regulated by MaSln1 is probably independent on the conserved MAPK pathway.Different gene expression analysis was performed to explore the mechanism of conidiation pattern shift.Of the 143 different expression genes(DEGs)that may be regulated by MaSln1,no gene related to the MAPK pathway was found.It was found that 22 of the 98 known DEGs regulated by MaSln1 were involved in mycelial growth,cell devision and cytoskeleton formation,indicating that MaSln1 is likely to regulate the expression of these genes related to cell division and morphogenesis,thus regulating the conidiation pattern shift in M.acridum.This study will provide essential insights into the molecular mechanism of the pathogenicity and conidiation pattern shift in filamentous fungi.