Analysis Of Terpenoids And Transcriptional Changes In Response To Fungal Infection In Chrysanthemum Morifolium Rmat.

Chrysanthemum(Chrysanthemum morifolium Ramat.),as one of the top ten traditional flowers in China and one of the top four cut flowers in the world,has important ornamental,edible and medicinal values.However,in the process of production and transportation,Chrysanthemum plants are often infected by pathogenic fungi,resulting in the loss of ornamental value and biomass.Terpenoids are the largest type of plant secondary metabolites that have diverse roles in plant defense against their natural enemies.Some terpenoids have been demonstrated to have antifungal effects,in which terpenoids are induced upon fungal infection to prevent further invasion of pathogenic fungi.Some terpenoids,particularly monoterpenes and sesquiterpenes,can be released from plants as volatile compounds and have been shown to play an important role in interactions between plants and their environment.Our understanding of the roles of volatile terpenes in plant-fungus interactions is limited.Therefore,the main objective of this thesis is to investigate the role of volatile terpenes in defense against fungi in chrysanthemum.Specific research results are as follows:1.To compare the resistance levels of Chrysanthemum plants to the fungus Alternaria tenuissima,the leaves of five cultivars of chrysanthemums(‘Boju’,‘Jinsihuangju’,‘Hangbaiju’,‘Huangshangongju’ and ‘Chuanbaiju’)were inoculated with A.tenuissima.According to the area of leaf spots,‘Boju’ was found to be the most resistant cultivar,whereas ‘Chuanbaiju’ was the least resistant cultivar.Then terpenoids in the leaves of the five cultivars were extracted using organic solvent and analyzed using GC-MS.In most cultivars,the resistance level was correlated to the contents of terpenoids.The potential correlations between total terpenes,monoterpenes,sesquiterpenes and several specific terpenes and leaf spot area were also analyzed.The results showed that the content of monoterpenes was significantly negatively correlated with leaf spot area.The contents of certain terpenoids were significantly negatively correlated with the degree of leaf damage,suggesting that they could play a certain antifungal role.Next,we profiled the volatile terpenoid released from chrysanthemum plants in a time course experiment after the infection by A.tenuissima.Compared to uninfected control plants,A.tenuissima-infected plants showed elevated emission of terpenoids.Interestingly,the rates of terpeneodi emission appear to be positively correlated to the level of susceptibility.Finally,PCA and correlation clustering analysis were performed.such as a type of terpenoid substances of the plants have been established and its release into the atmosphere after infected type induction terpenoid substances,i.e.,the type of terpenoid substance content of the plants is higher,the more easily infected with pathogenic bacteria,which are released into the atmosphere after illness,the lower the release rate of volatile terpenoid substances.2.After inoculation with another pathogenic fungus Fusarium oxysporum,terpenoids and salicylic acid were detected in the roots of cultivar ‘jinba’.The results showed that the SA and SAG contents in the leaves and roots increased significantly after inoculation with F.oxysporum.Two days after inoculation,the content of terpenoids in the roots of infected plants increased significantly.Of them,copaene,α-bergamotene and other sesquiterpenoids were induced.At 4 days after inoculation,the content of terpenoids in leaves reached the peak,which was significantly higher than that in control plants,and two monoterpenoids were found to be induced.It suggests that when F.oxysporum infects the root system of ’jinba’,the increased production of terpenoids is at least partly regulated by the SA signaling pathway.3.Transcriptome sequencing and expression level analysis were performed on leaves and roots of ’Jinba’ infected with Fusarium oxysporum.Eight terpene synthase(TPS)genes were identified.,Among them,two TPS genes Cm-j-TPS1 and Cm-j-TPS2 were significantly up-regulated,whereas Cm-j-TPS3,Cm-j-TPS4,Cm-j-TPS5 and Cmj-TPS6 appeared to be significantly down-regulated.In leaves,the expression levels of Cm-j-TPS7 and Cm-j-TPS8 were significantly up-regulated.Finally,the functions of the eight TPS were predicted by comparing with those of known TPSs from other plants.It was predicted that Cm-j-TPS1,Cm-j-TPS2,Cm-j-TPS3,Cm-j-TPS4 and Cm-j-TPS5 encode sesquiterpene synthases,Cm-j-TPS6 and Cm-j-TPS7 encode monoterpene synthases,and Cm-j-TPS8 encode a diterpene synthase.