Study On The Molecular Mechanism Of Grafting To Improve The Cold Tolerance Of Cucumbers

Cucumber?Cucumis sativus L.?is a typical chilling-sensitive vegetable crop,and the grafting can effectively improve its cold tollerance.However,the study of the molecular mechanism of grafting to improve the tolerance of cucumber is relatively scarce.In this study,white seed pumpkin is used as the root stock,and a chilling-sensitive inbred line‘09S007'of cucumber is used as the scion to elucidate the molecular mechanisms of chilling tolerance in grafted cuucumber.The second generation sequencing technology is used to deeply sequence the grafted and self-rooted seedling leaves under normal and cold stress,focusing on the mechanism of grafting improving of cucumber cold tolerance from photosynthetic pathways.Combined with this metabolic pathway,the photosynthetic parameters,chlorophyll fluorescence parameters and photosynthetic pigment content of the leaves are determined,which lays a molecular foundation for the comprehensive analysis of the cold tolerance of cucumber.The results are as follows:1.Cucumber grafted seedlings and self-rooted seedlings are placed in an incubator at 10°C/5°C for low temperature stress treatment to observe the appearance and morphological changes.The morphology of grafted seedlings leaves does not change significantly after low temperature for 24 hours.However,the self-rooted cucumber seedlings show wilting after 24 hours of low temperature treatment.The MDA content of grafted and self-rooted cucumber seedlings leaves increases with the prolonged time,and the latter is more obvious than the former.2.After low temperature,the net photosynthetic rate parameters of cucumber seedlings decreases,the transpiration rate slows,the stomatal conductance decreases,and the intercellular CO₂ concentration increases slightly.In addition,grafted seedlings perform better than self-rooted seedlings.3.The analysis of the content of the photosynthetic pigment shows that the content of carotenoids,chlorophyll a and chlorophyll b in leaves of grafted seedlings all decreases with the prolonged time,but the indicators of grafted seedlings are significantly higher than that of self-rooted seedlings.And there is a significant difference with the control which is placed at normal temperature.At the same time,grafted seedlings tend to have PSII higher maximum photochemical efficiency,PSII actual photochemical efficiency and photochemical quenching coefficient than self-rooted seedlings.4.By the deep sequencing of grafted seedlings and self-rooted seedlings under low temperature conditions,3274 differentially expressed genes are found.Among the grafted seedlings,515 genes are up-regulated,and 2759 genes are down-regulated.GO analysis shows that a total of 31 GO terms are significantly enriched,of which 12 GO terms are related to leaf photosynthetic characteristics.In the KEGG pathway analysis,a total of 1841 differentially expressed genes are enriched in 255 metabolic pathways,of which 41 pathways are significantly enriched,including photosynthetic-antennary pathways,plant pathogen interaction pathways,and photosynthesis pathways.The above metabolic pathways and photosynthetic physiological indicators showed good correlation.5.16 differentially expressed genes are selected for qRT-PCR validation analysis.The experimental results shows that the expression patterns of these differentially expressed genes are highly consistent with the transcriptome data,demonstrating the reliability of the transcriptome data and enabling follow-up research and analysis.