Enhancement of grape heat tolerance through VvbZIP36-mediated quercetin production

Basic leucine zipper (bZIP) transcription factors serve as crucial regulators in plants' response to abiotic stress; however, its function in grapevine heat tolerance is still largely unknown. Here, we undertook a comprehensive investigation of grape genome, leading to the identification of 65 VvbZIP genes, among which 16 VvbZIPs were significantly induced under heat stress. Overexpression of VvbZIP36 enhanced heat tolerance in grape calli, while virus-induced gene silencing (VIGS) of VvbZIP36 reflected thermal sensitivity. Additionally, we examined the metabolomic and transcriptomic profiles of grape seedlings, which showed that grapes exhibited increased accumulation of flavonoids, coinciding with the significantly induced expression of the VvFLS (Flavanol synthase) gene under heat stress. Overexpression of VvFLS also improved the heat tolerance in grape calli by scavenging reactive oxygen species (ROS). A yeast one-hybrid assay (Y1H) demonstrated that VvbZIP36 was capable of specifically activating the promoter of VvFLS, which was subsequently confirmed through a luciferase reporter assay. Furthermore, the overexpression of VvbZIP36 resulted in enhanced quercetin content, while the exogenous application of quercetin improved heat tolerance of grape. Collectively, our findings suggest that VvbZIP36 binds to the VvFLS promoter, thereby enhancing heat stress tolerance by increasing quercetin production and mitigating oxidative damage in grapes.