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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.

The plant growth regulator ethylene influences rachis browning in grape (Vitis vinifera L.). Although the ethylene signaling pathway is well defined, there is limited knowledge on its mode of action during rachis browning. Here, we show that an ethylene response factor (VvERF111) positively regulates chlorophyll degradation in rachis by binding to a DRE motif in the promoter of VvCLH1. The expression of VvERF111 and VvCLH1 in rachis was induced by ethylene and inhibited by 1-methylcyclopropene (1-MCP). VvERF111 belongs to the ERF IX subfamily of the APETALA2/ethylene responsive factor (AP2/ERF) superfamily, shows transcriptional activity in yeast, and is localized in the nucleus and membrane. The transient overexpression of VvERF111 or chlorophyllase (VvCLH1) in grape leaves accelerated chlorophyll degradation. In VvERF111-overexpressing leaves, transcript levels of VvCLH1 were also increased. Our findings offer a deeper understanding of the transcriptional regulation of chlorophyll degradation during the rachis browning of grape.

As a predominant phenolic compound in apple fruits, chlorogenic acid (CGA) benefits human health due to its various antioxidant properties. However, little has been known regarding the molecular mechanism underlying the CGA accumulation in apple fruits. In this study, we measured the CGA content and relative enzymes’ activities during fruit development in two different flesh-colored cultivars ‘Huashuo’ and ‘Red Love’. The CGA content in both cultivars decreased sharply from 30 days after full bloom (DAFB) to 60 DAFB. Notably, the CGA content in fruit flesh was relatively higher than that in the peel. Further, the activities of C3H and HCT enzymes downstream of the CGA biosynthesis showed the similar changing trend as CGA content. Based on the transcriptome data of ‘Huashuo’ fruit at 30 DAFB and 60 DAFB, 23 differentially expressed CGA synthesis-related genes were screened. Gene expression analyses further showed that MdHCT1/2/4/5/6 and MdC3H1/2/3 were positively correlated to the variation of CGA content in two cultivars. These findings establish a theoretical foundation for further mechanism study on CGA biosynthesis and provide guidance for nutrient improvement in apple breeding programs.