Overexpression of the sugar transporter VvHT5 in grapevine drives coordinated host–pathogen transcriptional reprogramming favoring Botrytis cinerea

Sugars are key modulators of plant-pathogen interactions, serving both as metabolic resources and as signaling molecules that influence defense outcomes. In grapevine (Vitis vinifera L.), the hexose transporter VvHT5, an ortholog of Arabidopsis thaliana STP13, is strongly induced during fungal infections, suggesting a role in host-pathogen interaction-related sugar partitioning. Here, we examined the function of VvHT5 in grapevine susceptibility to the necrotrophic fungus Botrytis cinerea. Transgenic lines overexpressing VvHT5 were generated in two cultivars, Thompson Seedless and Chardonnay, and displayed increased sugar uptake in leaves. Upon B. cinerea inoculation, these lines exhibited enhanced lesion development and fungal proliferation, contrasting with the tolerance phenotype previously observed in A. thaliana expressing VvHT5. Dual RNAseq analysis revealed that VvHT5 overexpression triggers a transcriptional landscape favoring carbohydrate metabolism, cell wall remodeling, and attenuation of defense responses, paralleled by upregulation of fungal genes involved in sugar acquisition and virulence. These results demonstrate that while VvHT5 contributes to restricting sugar availability to pathogens in A. thaliana, its constitutive activation in grapevine enhances host suitability for B. cinerea. Our findings highlight the complexity of sugar-mediated interactions and underscore the importance of host context in determining the outcome of plant-pathogen competition for carbon resources.