Doctorate thesis of Montpellier University

Tuesday december 14 at 2pm

Proton homeostasis in grape berry in relation to climate change


Doctorale school : GAIA – Biodiversité, Agriculture, Alimentation, Environnement, Terre, Eau
Spéciality : BIDAP – Biologie, Interactions, Diversité Adaptative des Plantes
Montpellier university


Team: KaliPHruit


Herman Höfte – Directeur de Recherche, INRAE – Rapporteur
Stéphanie Robert – Professeure, Univ.suédoise des sciences agricoles – Rapporteuse
Alexis De Angeli – Directeur de Recherche, CNR –  Examinateur
Jean-Luc Verdeil – Directeur de Recherche, Cirad – Examinateur
Maité Vicré-Gibouain – Maître de Conférence, Rouen – Examinatrice
Nadine Paris, Chargée de Recherche – CNRS – Directrice de thèse




Grapevine is one of the fleshy fruit species with the greatest socio-economic impact in the world. Its fruits, the grape berries, are mainly used for wine production. During development, grape berries accumulate water, sugars, organic acids, phenolic compounds and aromatic precursors which determine the quality at the harvest time. One of the quality markers of grapes is the acidity of the berry, which increases from pH2.5 to pH3.5 during development. This acidity results essentially from a balance between the vacuolar organic acids and their major counterion, potassium. The pH of the apoplast which plays a fundamental role in cell growth, also influences the membrane transport systems which control the loading of the berry. In the current context of climate change, the quality of wines is threatened. Indeed, the increase in temperatures leads to a drop in acidity and an excessive accumulation of potassium which at the end, strongly and negatively impacts the quality of the wines. Under these conditions, the study of the grape berries pH at the cellular level during development is essential and would help to provide knowledge on the mechanisms governing the acidity of grape berries. The main objective of my thesis was to analyze the distribution of protons at the cellular level in the vacuole and the apoplast where the pH is very acidic. My work therefore focused on the exploration of available chemical probes and on the development of genetically encoded pH sensors that are adapted to acidic pH: the Acidins. These approaches made it possible to measure the pH in the grape berry vacuole during its development. In addition, thanks to specific targeting signals, the Acidins were adressed to different apoplastic subdomains, either by anchoring to the plasma membrane or by secretion. In tobacco epidermis and in Arabidopsis, these apoplastic fusions made it possible to highlight the presence of pH subdomains. To extend the coverage of the apoplast explored by these pH sensors, we fused them to two cell wall proteins, including the flax pectin methylesterase LuPME1. Our preliminary results for these fusions suggested a link between the methylation degree of pectins and the apoplastic pH. These new apoplastic sensors open interesting perspectives for studying cell elongation in relation with pH variations at the subcellular scale as well as for the role of pH in regulating ionic exchanges at the plasma membrane

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