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Changes in Carbohydrate Metabolism in Plasmopara viticola-Infected Grapevine Leaves

¹UMR INRA1088 / CNRS 5184 / Université de Bourgogne Plante Microbe Environnement, 17 rue Sully, BP 86510, 21065 Dijon cedex, France; ²Laboratoire de Physiologie cellulaire végétale, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9, France; ³Laboratoire de Stress, Défenses et Reproduction des Plantes, URVVC–UPRES EA 2069, Bâtiment 18, Moulin de la Housse, BP 1039, 51687 Reims Cedex 2, France; ⁴IUVV–Université de Bourgogne-UMR INRA 1088/CNRS 5184/Université de Bourgogne Plante Microbe Environnement, 17 rue Sully, BP 86510, 21065 Dijon Cedex, France ⁵UPSP Proxiss–AGROSUP DIJON, 26 Bd Dr Petitjean, BP 87999, 21079 Dijon Cedex, France

The oomycete Plasmopara viticola is responsible for downy mildew, a severe grapevine disease. In infected grapevine leaves, we have observed an abnormal starch accumulation at the end of the dark period, suggesting modifications in starch metabolism. Therefore, several complementary approaches, including transcriptomic analyses, measurements of enzyme activities, and sugar quantification, were performed in order to investigate and to understand the effects of P. viticola infection on leaf starch and—to a larger extent—carbohydrate metabolism. Our results indicate that starch accumulation is associated with an increase in ADP-glucose pyrophosphorylase (AGPase) activity and modifications in the starch degradation pathway, especially an increased α-amylase activity. Together with these alterations in starch metabolism, we have observed an accumulation of hexoses, an increase in invertase activity, and a reduction of photosynthesis, indicating a source-to-sink transition in infected leaf tissue. Additionally, we have measured an accumulation of the disaccharide trehalose correlated to an increased trehalase gene expression and enzyme activity. Altogether, these results highlight a dramatic alteration of carbohydrate metabolism correlated with later stages of P. viticola development in leaves.