Folic acid delays postharvest quality deterioration of table grape by regulating cell wall metabolism-associated hub WRKY31 transcription factor

Grape (Vitis vinifera L.) berries are susceptible to quality deterioration after harvest. This study aimed to investigate the effect of folic acid (FA) treatment on the postharvest quality of table grape berries. Harvested 'Kyoho' (V. vinifera × V. labrusca L.) bunches were immersed in 1 mg L−1 FA solution for 15 min, then stored for sample collection and phenotype observation. Treatment with FA decreased the rates of berry abscission, water loss, and berry softening, reduced the accumulation of reactive oxygen species (ROS), and altered ROS metabolism-associated enzyme activities and gene expression levels. Transcriptome analysis revealed 507, 684, and 250 differentially expressed genes (DEGs) between FA-treated and non-treated berries at 3, 6, and 9 d after treatment, respectively. The DEGs were grouped into six modules according to a weighted correlation network analysis. A hub transcription factor, annotated as a WRKY transcription factor, was screened from the module associated with cell wall metabolism and identified as VvWRKY31. Transient transformation of grape berry slices revealed that overexpression of VvWRKY31 enhanced the relative expression level of VvRboh. The dual-luciferase assay showed that VvWRKY31 was capable of binding to VvRboh promoter. The present results provide insights into the potential molecular mechanism underlying FA-induced delay postharvest quality deterioration of grape berries. Specifically, FA inhibits expression of genes associated with ROS generation by reducing VvWRKY31 expression, thereby delaying quality deterioration induced by excessive accumulation of ROS. These results will be helpful in table grape breeding programs focused on delaying deterioration in postharvest quality.