Effects Of Pumpkin Rootstock On Traits Of Grafted Cucumber Self-Bred Progeny And Research On Genetic Variation Mechanism

In this study,‘Liangzhen No.1’ pumpkin（Cucurbita moschata Duch.）was used as the rootstock,and ‘Zhenghuang 1409’ cucumber（Cucumis sativus L.）was used as the scion to investigate whether grafting cucumber onto pumpkin could induce botanical traits variations in the self-bred progeny of grafted cucumber.Analysis of genomic DNA methylation changes of self-bred progeny of grafted cucumber by MSAP technology.High-throughput sequencing technology was used to analyze the differential gene expression of self-bred progeny of grafted cucumber.The results showed that the grafted of pumpkin and cucumber could induce heritable variation in the self-bred progeny of grafted cucumber.MSAP analysis found that the genomic DNA methylation level and status of the self-bred progeny of the grafted cucumber changed,Transcriptome analysis found that a large number of differentially expressed genes appeared in the self-bred progeny of grafted cucumber.The main results are as follows:（1）Compared with the cucumber scion inbred line,most of the traits of self-bred progeny of grafted cucumber were significantly different（p<0.05）;Compared with the cucumber scion inbred line,the first selfbred generation of grafted cucumber showed an overall variation trend of reduced length and width of the leaf at the node of the second female flower,tapered petiole and stem,increased internode length,shorter plants,decreased fruit diameter,longer fruit stalk,thicker pulp,decreased seed length and width,and lower100-grain weight.Most phenotypic traits of the second self-bred generation of grafted cucumber showed the same variation trend as those of the first self-bred generation.By observing plant phenotypic traits,two leaf phenotypic variations were observed in the first self-bred generation of grafted cucumber,and these two phenotypic variations were inherited in the second self-bred generation of grafted cucumber.（2）Compared with the cucumber scion inbred lines,the methylation levels of the two types of variant materials（variant I、variant II material）in the first and second self-bred generation of grafted cucumber were increased,however,the methylation level of single-strand outer cytosine or double-strand inner cytosine methylation of variant I or II compared with that of cucumber scion inbred lines from the first self-bred generation（G1）to the second self-bred generation（G2）showed nearly opposite changes;The methylation status of variant I or II showed opposite changes from G1 to G2,the degree of methylation of variant I in G1 was greater than the degree of demethylation,while the degree of demethylation of variant I in G2 greater than the degree of methylation,the degree of demethylation of variant II in G1 was greater than that of methylation,while the degree of methylation of variant II in G2 was greater than that of demethylation;Sequence gene homology analysis of specific fragments of MSAP found that the homologous genes mainly correspond to proteins containing specific domains,enzyme proteins and carrier proteins,etc.these functional proteins are involved in post-transcriptional regulation,cellular amino acid synthesis,redox and other processes,etc.the specific fragment of MSAP indicates that the methylation status of its homologous gene is mutated,which may affect the functional expression of its homologous gene,which may affect the growth and development process of the self-bred progeny of grafted cucumber,and even affect the phenotypic traits.（3）Compared with the cucumber scion inbred lines,there are a large number of differentially expressed genes in the two types of variant materials of the first self-bred generation of grafted cucumber;The GO function enrichment of differentially expressed genes showed that the differential gene expression of variant I was significantly related to plant stress and growth and development,and the differential gene expression of variant II was significantly related to plant photosynthesis;The KEGG enrichment pathway of differentially expressed genes showed that the differential gene expression of variant I was significantly correlated with signal transduction in plants,and the differential gene expression of variant II was significantly correlated with energy metabolism in plants;Screening of differentially expressed genes found that the two variant materials have more differentially expressed genes distribution in GO function enrichment nodes and KEGG pathway enrichment nodes related to auxin metabolism regulation and transport,differential expression of these genes may lead to changes in auxin levels in leaves,which can lead to variation in leaf phenotypes,it is speculated that the emergence of differentially expressed genes related to the regulation and transport of auxin metabolism in the two mutant materials may be the one reason for the leaf phenotype variation in the self-bred progeny of grafted cucumber.