Overexpression of the grape β-galactosidase gene VvBGAL3 delays the softening and extends the shelf life of tomato fruits

Grape softening is a complex process that is related to pectin degradation in the plant cell wall. β-galactosidases (BGALs) can degrade the galactose in rhamnogalacturonan (RG-I) pectin and plays an important role in fruit softening, but the functions of genes encoding BGALs during berry development and softening are still unclear. Fourteen VvBGAL genes were identified in the grape genome. Among them, VvBGAL3 was consistently more highly expressed in grape flesh that was still firm compared to soft grape flesh during berry development. Overexpression of VvBGAL3 increased fruit firmness and decreased the postharvest water loss in transgenic tomato fruits. Histological analysis indicated that pericarp thickness and the number of epidermal cell layers increased, and that there were more vascular sheath cells in the fruit mid-column of transgenic tomato fruits. Yeast one-hybrid and dual-luciferase reporter assays verified that VvNAC1 negatively regulated the transcription of VvBGAL3. In addition, overexpression of VvBGAL3 led to down-regulation of cell wall degradation-related genes at different stages of fruit ripening. Together, these results suggested that VvBGAL3 plays an important role in fruit development, fruit ripening and fruit softening and may serve as a target for future breeding programs.