Study On The Watermelon Grafting Healing Mechanism Affected By Rootstock Cotyledon

Grafting is an important measure to improve the ability of crops such as watermelon to resist soil-borne diseases and abiotic stress.However,the mechanism of graft healing is poorly understood.Rootstock cotyledon is an important part of watermelon grafting seedlings,but we also know little about how it affects the watermelon graft healing process.Watermelon inbred line “97103”(97103)was used in constructing different healing efficiency grafting combinations by self-grafted and grafted without rootstock cotyledon experiments to analyze the mechanism of influence of rootstock cotyledon on watermelon grafting healing,through the methods of transcriptome,endogenous auxin and sugar,exogenous auxin and sugar treatment.The research results were as follows:1.We analyzed the important response genes during watermelon graft healing process in RNA-Seq data.Results showed that the differentially expressed genes after grafting mostly enriched in hormone signal transduction and sugar metabolic pathways.At 6h、72h、120h and 168 h after grafting,54 and 99,34 and 59,67 and 90,31 and 61 differentially expressed genes were enriched in the hormone signal transduction pathway and sugar metabolism related pathway,respectively.All the results indicated the importance of carbohydrate and hormone substances for watermelon grafting healing.2.By comparing the graft survival rate of grafted watermelon seedlings with rootstock cotyledon,it was found that the graft survival rate of watermelon seedlings was significantly reduced from 90% to 2% by removing cotyledons of watermelon rootstock.Differentially expressed genes between the two different way of disposing of cotyledon rootstock mainly enriched in hormone signal transduction and sugar metabolism related pathways.There were 37,16,47 and 49 genes enriching in hormone signal transduction pathways and 75,45,79,and 68 genes enriching in sugar metabolism related pathways at6h、72、120h and 168 h after grafting.And most of these genes in the rootstock without cotyledon had lower gene expression than normal grafting treatment,indicating the removal of watermelon rootstock cotyledon would affect the expression of hormone and sugar related genes at the transcriptional level,thus affecting the watermelon graft healing.3.By exogenous IAA and sucrose adding to the rootstock which was grafted without cotyledon,we found 0.1m M IAA solution together with 2% sucrose solution treatment can significantly improve the watermelon graft survival rate reaching 81% and can also improve the relative expression of IAA response related genes,including IAA8b、IAA11a、IAA19、 ARF16c、 ARF16 d and SAUR1 at different timepoint after grafting.But the RNA-Seq results showed that these 6 genes down regulated after removing the watermelon rootstock cotyledon,as well as the content of endogenous IAA.The comprehensive results shew that the cotyledon in watermelon rootstock can affect the process of watermelon grafting healing by regulating the changes in the content of IAA and the expression of IAA responsive gene in the stock.However,further research is needed on how sugar affects grafting healing of watermelon and how it work together with IAA to promote grafting healing of watermelon.