Transcription Factor VlbZIP14 Inhibits Postharvest Grape Berry Abscission by Directly Activating VlCOMT and Promoting Lignin Biosynthesis

Sulfur dioxide (SO₂) is the most effective preservative for table grapes as it reduces the respiratory intensity of berries and inhibits mold growth. However, excessive SO₂ causes berry abscission during storage, resulting in an economic loss postharvest. In this study, grapes were exogenously treated with SO₂, SO₂ + 1.5% chitosan, SO₂ + 1.5% eugenol, and SO₂ + eugenol-loaded chitosan nanoparticles (SN). In comparison to SO₂ treatment, SN treatment reduced the berries' abscission rate by 74% while maintaining the quality of the berries. Among the treatments, SN treatment most effectively inhibited berry abscission and maintained berry quality. RNA-sequencing (RNA-seq) revealed that SN treatment promoted the expression of genes related to cell wall metabolism. Among these genes, <i>VlCOMT</i> was detected as the central gene, playing a key role in mediating the effects of SN. Dual luciferase and yeast one-hybrid (Y1H) assays demonstrated that VlbZIP14 directly activated <i>VlCOMT</i> by binding to the G-box motif in the latter's promoter, which then participated in lignin synthesis. Our results provide key insights into the molecular mechanisms underlying the SN-mediated inhibition of berry abscission and could be used to improve the commercial value of SO₂-treated postharvest table grapes.