Overexpression of MrMYB12 or MrMYB12/MrF3’5’H results in flavonol-rich tomato fruit that improves resistance against Botrytis cinerea during the shelf life period

Flavonols are one class of flavonoids that play a crucial role in regulating plant growth and promoting stress resistance. They are also important dietary components in horticultural crops due to their benefits for human health. However, flavonol levels in commonly consumed horticultural crops are insufficient to provide optimal benefits, and their role in regulating postharvest pathogen resistance in fruit remains poorly understood. In this study, overexpression of MrMYB12 or MrMYB12/MrF3'5'H from Morella rubra in tomato (Solanum lycopersicum) resulted in high accumulation of flavonols in fruit up to 3.2 g kg-1 by upregulating expression of genes involved in the phenylpropanoid pathway including SlPAL, SlC4H, Sl4CL, SlCHS1, SlCHI-like, SlF3H, and SlFLS. Transgenic tomato fruit showed high free radical scavenging activities including 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric ion reducing antioxidant power (FRAP) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and they also possessed excellent inhibitory effects against α-glucosidase. Postharvest storage experiments indicated that the flavonol-rich tomato fruit exhibited less surface shrinkage than wild type (WT), and they also showed decreased weight loss and increased antioxidant activity. Experiments of Botrytis cinerea infection showed that overexpression of MrMYB12 or MrMYB12/MrF3'5'H in tomato improved their resistance against B. cinerea during postharvest storage. Improvement of B. cinerea resistance in the flavonol-rich tomato fruit was associated with increase of superoxide dismutase (SOD) and catalase (CAT) enzyme activities and upregulated expression of defense-related genes such as SlPAL, SlβCA3, SlNPR1, SlPR1a, SlPR1b1, and SlPR3a. This study provides new insights for improving the nutritional value and postharvest pathogen resistance of horticultural crops by metabolic engineering.