Effects Of Methyl Jasmonate On Fruit Quality And Anthocyanin Biosynthesis Of ’Summer Black’ Grape(Vitis Vinifera L.)

Grape(Vitis vinifera L.)is one of the main fruit trees cultivated in China,with 85% of the cultivation area used for fresh grapes.Sichuan Province has become an important region for the grape industry in China.However,the unfavorable climate conditions of weak light,high temperature,and high humidity in the Sichuan Basin are limiting factors for improving the quality and efficiency of grape cultivation.In this experiment,8-year-old "Summer Black" grapes was used as the experimental material.Different concentrations of methyl jasmonate(Me JA)were applied at the onset of grape color veraison(45 and 52 days after flowering)to the grape clusters and leaves,with concentrations of 50 mg/L(M50),100 mg/L(M100),and 150 mg/L(M150),respectively,and equal amounts of water(CK)were used as a control.The dynamic changes in fruit quality,sugar and acid composition,phenolic substances,and total anthocyanin content in the development process of "Summer Black" grapes were studied under different concentrations of Me JA.Through transcriptome sequencing and weighted gene co-expression network analysis,key metabolic pathways and key node genes regulating the growth and development of "Summer Black" grapes by Me JA were identified,and the effect of Me JA on the anthocyanins synthesis related genes in "Summer Black" grapes was studied.These findings lay the foundation for the use of Me JA in "Summer Black" grapes and further research on its mechanism of action.The main research results are as follows:(1)Three concentrations of methyl jasmonate(Me JA)significantly improved the fruit quality of ’Xiahei’ grapes.Me JA treatment can increase the single fruit weight to a certain extent,with the M100 treatment showing a 10.31% increase in single fruit weight compared to the control after 73 days post-flowering.During fruit ripening,the M50 treatment had the highest soluble solid content,reaching 17.51%,which was 15.20%higher than the control.The sugar components in the grape skin and flesh were mainly glucose and fructose,with similar levels of both sugars.During the mature stage,the M50 treatment had the highest sugar component content,with glucose and fructose levels in the flesh 24.67% and 18.16% higher than the control,respectively.The main acid components in ’Xiahei’ grapes were malic acid,tartaric acid,and citric acid,with higher acid content in the skin than in the flesh.In the treatment groups,a different degree of reduction in malic acid and tartaric acid content was observed,while the citric acid content increased significantly.Compared to the control,the M50 treatment reduced the tartaric acid content in the flesh by 21.02%,malic acid content by 36.91%,and increased the citric acid content by 38.82%.Phenolic compounds in ’Xiahei’ grape fruits were mainly concentrated in the skin,and the content gradually decreased from veraison to maturity.The total phenols,total flavonoids,and total flavonols content in the skin of the treatment group were higher than those in the control during maturity,with the M50 treatment having 19.36% higher total flavonoids content than the control.(2)Methyl jasmonate can enhance the coloring effect and increase the total anthocyanin content of ’Summer Black’ grapes.As the fruit of ’Summer Black’ grapes gradually ripen,the color of the fruit surface changes from green to deep purple-black.At maturity,the fruit surface color of the M50 treatment group is darker,with lower brightness value(L*)and redness(a*)saturation,and higher yellowness(b*)saturation.At this stage,the total anthocyanin content in the grape skin is in the order of M50>M100>M150>CK,with the M50 group having a total anthocyanin content of 2307.43mg·kg-1,which is28.32% higher than the control group.Correlation analysis shows that the total anthocyanin content is highly positively correlated with the glucose,fructose,and citric acid content,and negatively correlated with the malic acid and tartaric acid content.(3)Transcriptome analysis was performed on fruit samples of ’Summer Black’grapes during the fruit ripening process,and a series of differentially expressed genes(DEGs)regulated by methyl jasmonate and their enriched pathways were identified.GO functional enrichment and KEGG clustering analysis of these DEGs revealed that they were primarily enriched in pathways related to photosystem efficiency,plant hormone signal transduction,starch and sucrose metabolism,and flavonoid and flavonol biosynthesis during early stages of development.By the mature stage,they were more prominently enriched in pathways related to plant hormone signal transduction,phenylpropanoid biosynthesis,and flavonoid and flavonol biosynthesis.Using the WGCNA analysis method,13 co-expression modules were constructed using 8,000 genes and used to detect their associations with measured phenotype indicators.Three coexpression modules,namely green,blue,and brown,were found to be highly correlated with the anthocyanin content and malic acid content,and node genes VIT＿09s0096g00090,VIT＿06s0080g00920,and VIT＿13s0067g03820 were identified from these modules using the Cytoscape software.(4)Methyl jasmonate significantly affects the biosynthesis pathways of flavonoids and flavonol in ’Summer Black’ grapes,thereby regulating the synthesis of anthocyanins.Transcriptome sequencing and real-time fluorescence quantification analysis revealed that methyl jasmonate treatment upregulates the expression levels of major structural genes PAL,CHS,CHI,F3’H,ANS,and UFGT in the anthocyanin biosynthesis pathway.The upstream regulatory genes MYBA1,MYBA2,and MYBA3 also showed a significant upregulation trend.