The Effect Of Hyperosmotic Stress On The Growth,Development And Pathogenicity Of Setosphaeria Turcica And The Regulatory Molecular Mechanism

Previous research in our laboratory found that hyperosmotic stress affected the colony morphology and mycelial growth of Setosphaeria turcica.However,there is no systematic study about the effects of hyperosmotic stress on the growth and pathogenicity of pathogen.In the present study,we will systematically elucidate the effects of hyperosmotic stress on the growth,development and pathogenicity of pathogen and its molecular mechanism.The main results were as follow.1.Hyperosmotic stress affects the mycelium morphology of pathogen and the morphology and yield of pathogenic conidium.The growth of colony of the wild-type strain 01-23 was significantly inhibited under hyperosmotic culture conditions.The interval length of aerial hyphae and basal hyphae of the pathogen turned shorter and the conidium production was significantly reduced under hyperosmotic culture conditions.The morphology of the conidium did not change significantly when the strain was cultered on PDA medium added 0.4 M NaCl or 0.4 M KCl,however,the length of the conidium widened when the strain was cultered on PDA medium supplemented with 0.6 M sorbitol.2.The vesicular of pathogen cells and flocculent material outside the cell wall increased under hyperosmotic stress.Observed under transmission electron microscopy,the intracellular vesicular and flocculent material outside the cell wall were increased after strains was inoculated in PDA medium supplemented with 0.4 M NaCl for 3 days.3.The invading hypha and pathogenicity of pathogen was changed under hyperosmotic stress.The pathogen were inoculated in hypertonic medium for 20 days,after which the resulting conidia were collected and observed.The results showed that the germination time of the conidium was ahead,the invading hypha formed by the conidium extended in bundles and rapidly extended,the onset time of the pathogen was advanced,and the pathogenicity was enhanced.The invading hypha of the pathogen were found to be bundle-like,which were cultured under PDA medium and treated with hyperosmotic stress.4.The HOG-MAPK pathway is involved in the regulation of pathogenic hyperosmotic stress responses.The results of RT-qPCR showed that StSTE11,StPBS2,StHOG1,StMSN2,StMSN4,StFPS1,StGPD1,and StGPP2,which were the key genes in HOG-MAPK pathway or downstream of the pathway,responded to hyperosmotic stress signals,indicating that these genes are involved in the hyperosmotic stress response of pathogens.5.The key genes of the HOG-MAPK pathway,StHOG1 and StFPS1,are involved in the regulation of appressorium formation and pathogenicity of pathogen.Analysis of the StHOG1 and StFPS1 mutants revealed that the pathogens could not penetrate cellophane and did not form appressors.6.The analysis of RNA-Seq data revealed that 5 ABC transporter genes in Setosphaeria turcica were involved in the response to hyperosmotic stress signals and infection process.