)mechanisms Of The Effects Of Arbuscular Mycorrhizal Fungus And Grass Endophyte On Leaf Spot Of Perennial Ryegrass

Leaf spot caused by Bipolaris sorokiniana is one of the mostly common diseases in perennial ryegrass.Arbuscular mycorrhizal fungi(AMF)and grass endophyte(Epichlo?)are two kinds of important symbiotic microorganisms.Previous studies have found that AMF and Epichlo? could improve the resistance of perennial ryegrass to leaf spot,however its physiological and biochemical,and the related molecular mechanism is unclear,which limited the application of use the two kinds of fungi to control the disease.In the present study,the effect of AMF Claroideoglomus etunicatum and Epichlo? on defensive enzyme activity and signal substance salicylic acid(SA)and jasmonic acid(JA)content were determined under greenhouse condition,and the differentially expressed genes related to plant disease resistance was analyzed via transcriptome technology.Moreover,WGCNA(Co-expression Network Analysis of Whole Added Genes)was used to analyze the network modules and function of the differentially expressed genes.The main research results are as follows:1.The infection of B.sorokiniana significantly decreased shoot biomass,N and P contents of ryegrass by 21.26%,11.53%,and 17.47%(P < 0.05).The presence of AMF significantly increased shoot biomass,N and P contents of ryegrass by 41.75%,20.26,and 54.48%(P < 0.05).AMF + Epichlo? significantly increased the shoot biomass,N and P contents of ryegrass by 11.91%,8.06%,and 38.96%(P < 0.05).However,the presence of Epichlo? had no significant effect on shoot biomass and P content of ryegrass.2.The presence of AMF C.etunicatum,Epichlo?,and AMF + Epichlo? reduced the disease incidence of leaf spot in perennial ryegrass by 39.47%,53.01%,and59.02%(P < 0.05),respectively.AMF significantly increased the activities of SOD,PPO,CAT and SA contents by 19.32%,21.19%,18.27%,and 48.32%,respectively.Epichlo? significantly increased the activities of SOD,PPO,POD,CAT and SA contents by 22.36%,30.96%,23.41%,28.26%,and 23.46%,respectively.AMF +Epichlo? significantly increased SOD,PPO,POD,CAT activities,and SA content by35.23%,45.96%,32.78%,41.01%,and 39.48%,respectively(P < 0.05).The presence of AMF C.etunicatum,Epichlo?,and AMF + Epichlo? significantly decreased JA content by 42.33%,15.12%,and 14.80%(P < 0.05),and significantly decreased MDA by 13.34%,12.58%,and 26.71%(P < 0.05),respectively.3.Transcriptome results showed that the presence of AMF regulates the expression of genes related to photosynthesis,carbon fixation,amino acid metabolism and other processes.900 genes were found in the module associated with AMF group,which contains 145 transcription factors(TFs)up-regulated and 226 plant resistance genes(PRGs).And most of the up-regulated TFs related to plant growth and development,information transfer,and fruit mature,such as C3 H RWP-RK,C2C2-GATA,MYB,MADS,GEBP,ARF,ARR-B,BES1,BSD,C2C2-CO-like,etc.Among the screened 25 hub genes,two plant growth-related transcription factors,C3 H and RWP-RK,were associated with AMF significantly increased the biomass of ryegrass.The reduction of the disease incidence of ryegrass by AMF was related to one HSF transcription factor and one PRG in the hub gene.Also,the differential genes induced by AMF were related to the up-regulated genes related to SOD,PPO,CAT,and SA synthesis.4.The presence of Epichlo? regulates the expression of genes related to phenylpropanoid biosynthesis,lignin,ABC transporter,and flavonoid biosynthesis.These substances are mainly involved in plant defense and material transport processes.281 genes associated with Epichlo? categorized into network module,which contains 60 TFs and 102 PRGs.8 PRGs that involved in plant disease resistance and 1 HSF transcription factor were found in the hub genes,which is associated with the fact that the presence of Epichlo? significantly improves plant disease resistance.Besides,Epichlo? also improves plant disease resistance via regulating the expression of genes related to SOD,PPO,POD,CAT,and SA.5.AMF + Epichlo? significantly improves plant growth and disease resistance.The results of differential expression gene analysis showed that AMF + Epichlo?regulates the expression of genes related to terpenoid skeletal biosynthesis,biotin metabolism,ascorbic acid metabolism,aldehyde acid metabolism and plant-pathogen interaction proteins.WGCNA results show that 370 genes associated with AMF +Epichlo? categorized into network module,which contains 54 TFs and 124 PRGs respectively.11 PRGs and 1 HSF transcription factor were found in the 27 hub genes,which is the important reason that AMF + Epichlo? have higher disease resistance.Besides,AMF + Epichlo? also up-regulated expression of genes related to SOD,PPO,POD,CAT,and SA.HSF transcription factors were found in the hub genes of each of the three modules.The results showed that the HSF transcription factor played an important role in AMF and Epichlo? resistance to perennial ryegrass leaf spot.