| The Vernicia fordii(Hemsl.)Airy Shaw(tung oil tree,tung tree)and Vernicia montana(Wils.)Lour(woody tung oil tree,tung tree)are two traditional chemical oil species in China,which have been cultivated for thousands of years.Tung oil,extracted from seeds of Vernicia species,is high-quality oil with renewable,clean and safe characteristics.Chinese produces about 80,000 ton of oil per year,and China has 40% of the world market now.The V.fordii is main cultivated species,which featured with characters of fast growth,early fructification and high yield.However,the tung tree industry has been deeply influenced by Fusarium wilt disease.Tung wilt disease is induced by a fatal and soil-borne fungal pathogen Fusarium oxysporum f.sp.fordii(Fof-1)in V.fordii.Until now the disease has occurred in more than 90 counties and cities of eight provinces in China and had serious threat to nearly one million hectares of national tung oil trees.Compared with V.fordii,the V.montana has high resistance ability to Fusarium wilt pathogen,although its oil production and quality are relatively low-grade.Therefore,the study of root defense ability in V.montana can provide ideas for the Fusarium wilt prevention and breeding of disease resistance.In this thesis,the inhibitory effect on pathogen Fof-1 of root and lateral root xylem in V.montana were investigated.Combined with electron microscopy,transcriptomics and metabolomics,the related compounds and pathways in response to pathogen Fof-1were analyzed.The main findings are as follows:(1)We found that the root extract of V.montana showed the chemical defense effect on the growth of pathogen Fof-1.Based on this,analysis of root metabolites showed that the flavonoid content of root is higher(30.19%)in V.montana after the pathogen Fof-1 infection.Among them,the fold change of formononetin 7-O-glucoside(belong to isoflavone)and hesperetin 7-rutinoside(belong to flavanone)in V.montana reached 2026.26 and 1185.52,respectively.The KEGG enrichment analysis of differentially up-regulated genes at the early stage of Fof-1infection showed that up-regulated genes in V.montana were significantly(P value,0.0191704)enriched into the pathway of “phenylpropanoid biosynthesis” and the “flavonoid biosynthesis”pathway was also enriched(p value =0.213168).There are four hub genes in two pathways,including 4-coumarate: CoA ligase(4CL),β-D-xylosidase,β-glucosidase,and peroxidase N1,which are highly connected with the other 1625 genes.Altogether,after the pathogen Fof-1infection,genes related to flavonoids and phenylpropanoids biosynthesis pathways were upregulated.Then,the content of flavonoids increased and was significantly higher than V.fordii,which played a chemical defense role in the process of Fof-1 infection.(2)Based on results of the transmission electron microscope,the lateral root xylem of V.montana were found to be the key position for the block of Fof-1infection in the roots.During the process of Fof-1 infection in V.montana and V.fordii,a great number of hyphae were appeared in the xylem cell of V.fordii while not found in that of V.montana.And the cell wall of root xylem in V.fordii was observed to be broken and dissolved at the late stage of Fof-1 infection.Moreover,the thickness of xylem cell wall in V.montana was thicker compared with that of V.fordii,and the xylem cell wall was happened to be thickened after the Fof-1 infection in V.montana.Accordingly,in V.montana,the content of lignin and hemicellulose was higher than V.fordii and was up-regulated after Fof-1 infection.Furthermore,compared with the root exact of V.montana,the root xylem extract of V.montana exhibited the more obvious chemical defense effect on the growth of pathogen Fof-1.This result indicated that the chemical defense effect of roots was mainly achieved through the xylem of the lateral root V.montana.Together,in V.montana,the root xylem cell wall plays a physical and chemical defense during the pathogen Fof-1 infection,and the lignin and hemicellulose might contribute to the thickness of the cell wall.(3)To further investigate the chemical and molecular basis of the physical and chemical resistance ability,we conducted the metabonomics and transcriptomics analysis of the lateral root xylem of V.montana and V.fordii in the four periods of Fof-1 infection.The expression analysis of metabolite found that the up-regulated metabolites in V.montana were significantly higher than those of V.fordii.Consistent with the metabonomic result of root,the KEGG enrichment analysis of differential metabolites in V.montana showed that the metabolites related to “flavonoid biosynthesis” pathway were distinctively up-regulated in the middle and late stage of Fof-1 infection,including naringenin,catechin,taxifolin,myricetin and so on.Similarly,the KEGG and GO enrichment analysis of the up-regulated genes after Fof-1infection revealed that the "flavonoid biosynthesis" pathway associated with Fusarium wilt resistance was significantly enriched.And the pathway related to cell wall synthesis was also enriched in GO enrichment analysis,including “UDP-glucosyltransferase activity”,“glucosyltransferase activity”,“glutathione transferase activity” and so on. |
