VvPL11 Is a Key Member of the Pectin Lyase Gene Family Involved in Grape Softening

Abstract

Fruit ripening includes several metabolic changes that lead to sweeter and softer fruit. Pectin depolymerization is one of major factors that softens developing grape berries. Pectin lyases (PLs) play important roles in pectin degradation in the grape berry. However, little is known about the temporal and spatial expression of grapevine (Vitis spp.) pectin lyase genes (VvPLs) or their function during fruit ripening and softening. In this study, 18 individual VvPL genes were identified in the grape genome. All VvPL genes were sorted into group I and group II, except VvPL12 which demonstrated higher and similar expression trends in different tissues and organs. In grape berry, VvPL1, 5, 7, 11 and 16 were highly expressed, whereas VvPL18, 15, 2, 13, 10, 14, 17, 6 and 8 showed lower expression levels at different berry developmental stages. Expression of VvPL11 firstly increased and then decreased, and the highest expression was shown at 6 weeks after full bloom (WAFB) during berry development. Over-expression of the VvPL11 gene in tomato caused higher ethylene production and lower firmness compared to wild-type fruit. Moreover, decreased propectin and increased water-soluble pectin (WSP) levels were observed in VvPL11 transgenic tomato fruit. Consistent with this result, the expression levels of SlPG2, SlEXP, and SlPME1, all of which are genes involved in fruit softening, were up-regulated in VvPL11-OE tomato fruit, which supported the idea that VvPL11 plays an important role in fruit ripening and softening. This study provided a comprehensive analysis of the grapevine PL family and advanced our knowledge of the functions of VvPLs during fruit softening.