Mechanism In Effects Of Grafting Onto Artemisia Scoparia On Aphid Resistance In Chrysanthemum

In this study,Artemisia scoparia.with high aphid resistance was selected as the rootstock,and chrysanthemum cultivars ‘Hangbaiju' was used as scion.We used the RNA-Seq platform to perform a de novo transcriptome assembly to analyze the self-rooted chrysanthemum(Chrysanthemum morifolium 'Hangbaiju')and the grafted Artermisia-chrysanthemum transcription response to aphid stress.And the effects of volatile substances,defense enzymes activity,concentration of plant hormones and metabolites on aphid resistance of grafted and self-rooted seedlings were compared and analyzed.These data will contribute to further studies of aphid tolerance and the exploration of new candidate genes for chrysanthemum molecular breeding.The main results were as follows:1.Aphid population statisticsGrafting onto Artemisia scoparia.significantly reduced the number of aphids.On the 7th day,the number of the aphids on the grafted seedlings was about 54.4% of the self-rooted seedlings which showed a significant difference.On the 10 th day,the average number of the aphids on the grafted and the self-rooted seedlings were 59.6 and 119.8,respectively.2.Study on nutrient substance in leaves of tested materialsAfter grafting treatment,a higher concentration of soluble sugar was observed in the grafted seedlings than in the self-rooted seedlings at the same time point after infestation.The content of soluble sugar in the grafted and self-rooted seedlings increased by 34.12% and11.22%.And the content of soluble protein in the grafted and self-rooted seedlings decreased by 31.09% and 19.95% within 6 h of infestation with aphids,respectively.3.Study on the change of defense enzyme activity of tested materialsThe activities of defensive enzymes(SOD,POD,LOX,PAL and CAT)were significantly increased by aphid infestation and higher in the grafted and self-rooted seedlings after inoculated the aphids,and the activities were still on a high level in a long time after infestation.4.Study on secondary metabolism substances in leaves of the tested materialsIn the present study,after aphids infestation,flavonoid accumulation was detected in the leaves of the grafted and self-rooted plants.The level of flavonoids increased after 6 h ofinfestation,and a higher concentration of flavonoid was observed in the grafted plants than that in the self-rooted plants.And the results showed that the varieties and relative contents of terpenoids in the grafted and self-rooted plants were significantly different.5.Study on the concentration of the plant hormones of tested materialsThe content of SA in the grafted plants was higher than that in the self-rooted plants before and after aphids infestation.However,there was only a significant difference in the content of JA of the grafted and self-rooted seedlings after aphids infestation.6.Differential expression genesThe results indicated that there were 1337 differentially expressed genes(DEGs)in the grafted seedlings compared to the self-rooted chrysanthemum.Among them,there were 504 genes with different expression in B0 compared to A0,of which 134 genes were upregulated and 370 genes were downregulated;620 genes were differentially expressed in B1 compared to A1,of which 457 genes were upregulated and 163 genes were downregulated;and 223 genes were differentially expressed in B2 compared to A2,with 89 upregulated genes and 134 downregulated.7.Functional classificationAccording to the GO classification,cell part,dicarboxylic acid biosynthesis,oxidordeuctase,transferase,hydrolase,protein kinase,terpene synthase,transporters,binding protein,phospholipase inhibitors and lipase inhibitor genes were identified.The results of the KEGG pathway classification were mainly including photosynthesis,trans-linolenic acid metabolism,pantothenic acid and CoA biosynthesis,plant hormone signal transduction pathways,phenylpropane biosynthesis,betaine synthesis,monogamous biosynthesis,sucrose metabolism,flavonoid biosynthesis and plantpathogen interactions.8.The results indicated that grafting chrysanthemum onto A.scoparia.resulted in enhanced resistance to aphids,which was closely related to the regulation of metabolic pathways,secondary metabolic biosynthesis,immune response and signal transduction.These genes provided reference data for the study of aphid stress regulation mechanism in chrysanthemum and the breeding of aphid resistant varieties.