Overexpression of the sugar transporter VvHT5 turns grapevine into a better host for 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), the hexose transporter VvHT5, an ortholog of Arabidopsis thaliana STP13, is strongly induced during fungal infections, suggesting a role in defense-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 RNA-seq 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 Arabidopsis, 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. HIGHLIGHTSO_LIVvHT5 overexpression increases Botrytis cinerea susceptibility in grapevine C_LIO_LIDual RNA-seq uncovers coordinated transcriptional shifts in host and pathogen C_LIO_LIVvHT5 reprograms sugar partitioning and defense-associated metabolism C_LIO_LIContrasting STP13-like responses between grapevine and Arabidopsis C_LIO_LISugar uptake activity of VvHT5 promotes fungal access to host carbon C_LI