Targeting genes involved in the organic acid metabolism of grape berry

Abstract

Global warming accelerates the loss of acidity in grape berries (Vitis vinifera), a critical parameter for wine quality and sensory freshness. During early development, organic acids (mainly malate and tartrate) are accumulated at high levels in the vacuole compartment of mesocarp cells, whereas at the onset of ripening, a sharp decline in acidity and a concomitant rise in pH occur. This decline is driven bytwo primary factors: the respiratory degradation of malate during ripening and its chemical neutralization by potassium ions (K⁺)accumulating in the vacuole. This PhD project aims to explore three strategic intervention points for stabilizing or enhancing grapeacidity through the identification and functional characterization of candidate genes involved in enhancing vacuolar sequestration,reducing K⁺-driven neutralization and preventing malate efflux from the vacuole.

Leveraging knowledge from model systems like tomato and apple, promising candidates to target have been prioritized through comparative genomics and analysis of existing grape berry transcriptomic datasets. For vacuolar loading, the Aluminum-Activated Malate Transporter (ALMT) family and their potential transcriptional repressors (e.g., members of the WRKY family) are key candidates for investigation. To counteract K⁺ influx, potassium transporters belonging to the Shaker (e.g., VvK1.2) and KUP/HAK/KT familiesrepresent promising targets. For the still poorly understood mechanism of malate efflux, the Tonoplast Dicarboxylate Transporter (TDT) family in grape (VvTDTs) and tonoplast-associated protein kinases that may regulate their activity are promising targets for investigation. Preliminary expression analysis of these candidates across publicly available RNA-seq datasets reveals distinct temporal patterns during berry development. Some of these candidates show interesting expression profiles, with peaks at early ripening stages, as observed for certain potassium transporters or TDT family members. This project will validate the function of selected targets through heterologous systems and, ultimately, via targeted mutagenesis in grape, aiming to develop climate-resilient cultivars with superior and stable acidity.

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