Soutenance de thèse de Xi ZHAN - lundi 8 décembre 2025 à 14h

Xi ZHAN soutiendra sa thèse intitulée "Deciphering the metabolic fingerprint of grapevine berries under high temperature".

La présentation orale se déroulera en anglais, et la discussion avec le jury aura lieu de préférence en français. 

La thèse en 300 mots 

This work, conducted within the UMR EGFV (QualyGrapE team), aims to elucidate the physiological and metabolic adjustments that enable berries to respond to high temperatures (HT). Initially focused on berry redox balance under HT, the study was subsequently reoriented toward a broader metabolic characterization due to both technical limitations in enzymatic assays of berry and the inherent complexity of functional gene analysis in grapevine. These experimental constraints, however, opened a more integrative perspective for my PhD project: since metabolites act as the bridge between genotype and phenotype, they not only determine fruit quality attributes such as color, flavor, and aroma, but also play direct roles in stress perception, signaling, and defense. Consequently, metabolite profiling emerged as a powerful and biologically meaningful approach to investigate how grape berries adjust their metabolism under HT. The research comprises three main parts.

The first compares Cabernet-Sauvignon and Merlot, two cultivars differing in their putative thermosensitivity, with a focus on polyphenolic compositions. Using targeted LC-MS analyses at distinct developmental stages under controlled conditions, we established a detailed polyphenolic profile of both cultivars under varying HT durations.

The second part expands this comparison through untargeted LC-MS and targeted GC-MS metabolomic approaches, capturing a broad range of primary and secondary metabolites and enabling the identification of robust metabolite markers associated with heat exposure.

Finally, the study tentatively explores the functional characterization of a peroxidase gene potentially involved in redox regulation and anthocyanin degradation under HT. A CRISPR-Cas9-based strategy was developed to generate stable transgenic microvine lines for functional validation.

Together, our findings provide new insights into the metabolic remodeling of grape berries under high temperature and highlight both common and cultivar-specific adaptive responses. The identified metabolite markers offer valuable leads for developing viticultural strategies and breeding programs aimed at improving heat resilience in grapevine.