Expressional diversity of grapevine 3-Hydroxy-3-methylglutaryl-CoA reductase (VvHMGR) in different grapes genotypes.

BACKGROUND: 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) is a key enzyme in the mevalonate (MVA) pathway, which regulates the metabolism of terpenoids in the cytoplasm and determines the type and content of downstream terpenoid metabolites. RESULTS: Results showed that grapevine HMGR family has three members, such as VvHMGR1, VvHMGR2, and VvHMGR3. The expression of VvHMGRs in 'Kyoho' has tissue specificity, for example, VvHMGR1 keeps a higher expression, VvHMGR2 is the lowest, and VvHMGR3 gradually decreases as the fruit development. VvHMGR3 is closely related to CsHMGR1 and GmHMGR9 and has collinearity with CsHMGR2 and GmHMGR4. By the prediction of interaction protein, it can interact with HMG-CoA synthase, MVA kinase, FPP/GGPP synthase, diphosphate mevalonate decarboxylase, and participates in the synthesis and metabolism of terpenoids. VvHMGR3 have similar trends in expression with some of the genes of carotenoid biosynthesis and MEP pathways. VvHMGR3 responds to various environmental and phytohormone stimuli, especially salt stress and ultraviolet (UV) treatment. The expression level of VvHMGRs is diverse in grapes of different colors and aroma. VvHMGRs are significantly higher in yellow varieties than that in red varieties, whereas rose-scented varieties showed significantly higher expression than that of strawberry aroma. The expression level is highest in yellow rose-scented varieties, and the lowest in red strawberry scent varieties, especially 'Summer Black' and 'Fujiminori'. CONCLUSION: This study confirms the important role of VvHMGR3 in the process of grape fruit coloring and aroma formation, and provided a new idea to explain the loss of grape aroma and poor coloring during production. There may be an additive effect between color and aroma in the HMGR expression aspect.

The Effect of Ethylene on the Color Change and Resistance to Botrytis cinerea Infection in 'Kyoho' Grape Fruits.

The formation of grape quality and the mechanism of resistance against foreign pathogens affect the storage stability of fruits during post-harvest handling. Ethylene plays a crucial role in regulating the ripeness of fruits and can be used as an exogenous regulator to resist exogenous pathogens. In this study, we used different concentrations of ethephon for treatment of grape fruits before veraison, analyzed the anthocyanin content, soluble solids, titratable acid, and determined fruit firmness and cell wall metabolism-related enzymes during fruit development. Results showed that exogenous ethephon promoted the early coloration of grape fruits and increased the coloring-related genes myeloblastosis A1(MYBA1), myeloblastosis A2(MYBA2), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase gene (F3'H), flavonoid 3', 5'hydroxylase (F3'5'H), 3-O-flavonoid glucosyltransferase (UFGT), and glutathione S-transferase (GST), softening related genes Polygalacturonase(PG), pectinate lyases(PL) and Pectin methylesterase( PME, as well as ethylene metabolism pathway-related genes 1-aminocyclopropane-1-carboxylic acid synthase 1(ACS1), 1-aminocyclopropane-1-carboxylic acid oxidase 2 (ACO2), ethylene receptor gene(ETR2), and ethylene-insensitive 3 (EIN3). Ethephon treatment also increased soluble solids and decreased titratable acid in grape fruit. Fruits pretreated with ethephon were inoculated with Botrytis cinerea, which led to resistance in grape fruit through activation of the antioxidant system. The expression levels of disease resistance-related genes including VvPAD4, VvPIP1, VvNAC26, VvDREB, VvAPX, Vvpgip, VvWRKY70, VvMYC2, VvNPR1 also increased in inoculated fruit with pathogen following ethephon pretreatment. Furthermore, we monitored ethylene response factor 1(ERF1) transcription factor, which could interact with protein EIN3 during ethylene signal transduction and mediate fruit resistance against B. cinerea infection. Meanwhile, overexpression of VvERF1 vectorin strawberry fruits reduced the susceptibility to B. cinerea infection. We suggest that ethylene can induce resistance in ripened fruits after B. cinerea infection and provide adequate postharvest care.