The Defense Strategies Of Resistant And Susceptible Tea Cultivars In Response To Empoasca Onukii Feeding

The small green leafhopper,Empoasca onukii(Matsuda),is a major pest of tea plants(Camellia sinensis(L.)O.Kuntze)in China,its damage seriously affected the quality and yield of tea.At present,there were few studies on the defense mechanism of tea plant respond to E.onukii feeding,and the molecular mechanism is still unclear.In this study,a resistant tea cultivar Juyan(JY)and a susceptible tea cultivar Enbiao(EB)were Used as the materials,the differential expression genes(DEGs)were screened and their expression changes were analyzed,by comparing the transcriptome of the two tea cultivars at different time points of continuous feeding of leafhoppers,to found out the related defense pathways which were triggered by tea plant in response to leafhopper.Furthermore,to reveal the induced defense mechanism of tea plant by leafhopper feeding,the dynamic change of main volatiles of tea at different time points of leafhopper feeding were measured,and the content of secondary metabolites of lignin and the related enzyme activity were also analyzed,The study will provide abundant genetic resources for the breeding of resistant tea cultivars,and deepen the understanding of the theoretical system of tea plant-insect interaction mechanism.The main results are as follows:1.The defense response of the resistant and susceptible tea cultivars under E.onukii feeding.The molecular mechanism of tea resistance induced by leafhoppers was revealed in this study,by comparing the dynamic changes of transcriptomes of resistant and susceptible tea cultivar at different time points(0h,6h,12 h,24h)of leafhoppers feeding.The results showed that the numbers of DEGs in the susceptible tea cultivar EB were higher than those in the resistant cultivar JY at 6h and 24 h of leafhopper feeding.The numbers of DEGs of the two cultivars reached the maximum at 12 h of leafhopper feeding.Pathway enrichment analysis of GO and KEGG showed that the stress responses of the two tea cultivars induced by leafhoppers were similar.However,jasmonic acid(JA)-related genes were significantly up-regulated in the resistant cultivar at the early stage(6h),the terpene biosynthesis pathway and the ?-linolenic acid pathway were activated earlier in the resistant cultivar,and lasted for 24 h.Our results confirmed that after leafhopper damage,the resistant tea cultivar activated its defense responses earlier than the susceptible cultivar,and these defense responses were mainly related to terpenoid metabolism and JA biosynthetic pathway.2.The volatiles emission of the resistant and susceptible tea cultivars under E.onukii feeding.Dynamic headspace collection and GC-MS technique were used to detect the content of tea volatiles whihc induced by leafhopper at different time points(6 h,12 h,24 h,36 h,48 h,72 h).The results showed that the content of the major volatiles,including(Z)-3-hexenyl ester,ocimene,DMNT,linalool,caryophyllene and TMTT,were greatly affected by leafhopper feeding.Among them,content of monoterpenoids are higher in EB,while content of sesquiterpenoids are higher in JY.According to the previous transcriptome data,after leafhopper damage,most of genes in terpenoids synthesis were up-regulated in the two tea cultivars.And the mono-and diter-terpenoids content and the relative genes were highly expressed in EB.Therefore,leafhoppers feeding can induce the expression of the related genes in the synthesis pathway of terpenoid volatiles,thus affecting the production and release of terpenoids in tea plants.3.Analysis of the lignin metabolites of the resistant and susceptible tea cultivars under E.onukii feeding.The secondary metabolites of lignin were analyzed by HPLC-MS/MS.The results showed,in healthy tea plants(0 h),the content of phenylalanine,coumaric acid and ferulic acid of JY were significantly higher than those in EB,and the activity of CAD enzyme in JY were significantly higher than it in EB.After treatment of leafhopper feeding,the enzyme activities of PAL,4CL,CAD and POD were significantly increased in two tea cultivars.The content of phenylalanine and 5-hydroxyconiferyl alcohol in JY were increased significantly,and the content of ferulic acid and 5-hydroxyconiferyl alcohol in EB were also significantly increased.Leafhopper feeding activated most of the related genes in phenylpropane biosynthesis pathway,the expression of PAL?C4H?4CL?CCo AOMT in JY were slightly higher than those of EB after treatment of leafhopper feeding,but the difference was not significant.It was concluded that resistant tea cultivar activated the defense response earlier than susceptible tea cultivar,this defense response was mainly related to terpenoids and JA synthesis.Tea plant also activated the phenylpropane biosynthesis pathway and promote the production of more lignin metabolites to against leafhopper feeding.