The study was performed to determine the mode of β-aminobutyric acid (BABA)-induced disease resistance and to analyze the mechanism involved in BABA-mediated accumulation of soluble sugar on the basis of sorbitol metabolism and transcriptional regulation in postharvest grapes.The punched wounds in each berry were injected with 10 mmol/L BABA solution, 1.0×105 spores/mL spore suspension of Botrytis cinerea or BABA, followed by pathogenic inoculation.Afterwards, the grapes were stored at 20 ℃ for 5 days.The tissue samples were taken daily for assessment of disease occurrence and measurement of molecular and biochemical parameters involved in quality, resistance response, and sorbitol metabolism.Results showed that treatment of grapes with BABA alone could induce a defensive response at the basal level;however, the transcriptional values of PRs genes (VvNPR1, VvPR1, VvPR2, and VvPR5) and the content of individual phytoalexins in BABA-treated grape berries were significantly enhanced upon inoculation of the berries with B.cinerea, indicating that the resistance induced by 10 mmol/L BABA could be attributed to a priming mechanism in grapes since only the BABA-treated fruit showed an enhanced capacity to augment defence responses upon challenge with the pathogen.On the other hand, BABA treatment promoted the activities of a set of sorbitol metabolism-related enzymes, including S6PDH, NAD+-SDH, NADP+-SDH, and SOX, resulting in the accelerated conversion of sorbitol into glucose and fructose.Meanwhile, VvWRKY40 bound to the W-box motif in the promoter of sucrose-metabolizing enzyme genes and activated their transcription, by which BABA indirectly enhanced sucrose synthesis in grapes.Therefore, BABA elicitation not only activated priming resistance to inhibit gray mold disease in grapes during storage but also promoted the accumulation of soluble sugars through the regulation of sorbitol metabolism and transcriptional activity of VvWRKY40, which suggested that the BABA-triggered priming response could exert a balance between elevated disease resistance and maintenance of primary metabolism.
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