Vv14-3-3ω Is a Susceptible Factor for Grapevine Downy Mildew

14-3-3 proteins are highly conserved regulatory molecules in plants. In grapevine (Vitis vinifera L.), 14-3-3 proteins are studied under abiotic stress. However, the role of 14-3-3 proteins in the interaction between grapevine and downy mildew is yet to be studied. In this study, we identified a highly conserved 14-3-3 protein in grapevine and performed a phylogenetic analysis, revealing a close relationship between one of its homologs, 14-3-3ω proteins from Arabidopsis thaliana and Nicotiana benthamiana. We designated this homolog as Vv14-3-3ω. Subcellular localization studies showed that Vv14-3-3ω resides in the plasma membrane and cytoplasm. Expression analysis revealed a strong induction of Vv14-3-3ω at early time points following Plasmopara viticola infection, correlating with enhanced pathogen sporulation in grapevine. Furthermore, transient overexpression of Vv14-3-3ω in N. benthamiana increased susceptibility to the Phytophthora capsici pathogen and suppressed Flg22-induced pattern-triggered immunity (PTI) responses. Overexpression of Vv14-3-3ω in Nb14-3-3-silenced N. benthamiana plants resulted in increased susceptibility to P. capsici, suggesting functional conservation of this isoform. These findings indicate that Vv14-3-3ω functions as a susceptibility factor, facilitating pathogen infection and disease progression in grapevine, and highlight its potential role for improving resistance against downy mildew.