S20 - Session P3 - Untargeted metabolic profiling of leaves of Vitis vinifera L. plants with brown wood streaking and varying levels of symptom severity of grapevine leaf stripe disease (Esca complex)

Authors: Piebiep Goufo *, Isabel Cortez

Metabolites represent small biomolecules that serve various biological functions in plants. The grapevine plant accumulates numerous molecules that act as key components of the plant defense system against diseases. In this study, 513 metabolites were extracted and separated from the leaves of grapevines using a multiplexed GC- and UHPLC-tandem MS (MS/MS 2 ) platform. The platform is based on a couple of extraction steps and five independent chromatographic injections optimized for free fatty acids, hydrophilic, hydrophobic, basic, and polar compounds. Identification of 85% of metabolites was based on multiple orthogonal criteria to a unit mass spectral library of ca. 10 000 MS/MS spectra built from authentic reference compounds. Relative levels of these metabolites were determined in four different leaf groups of vines expressing or not symptoms of esca complex disease: leaves of unaffected vines (healthy), leaves of wood-affected vines (asymptomatic), and leaves of affected vines (symptomatic) with varying degrees of damage i.e., chlorotic and scorched leaves. Using a random forest approach to identify candidate metabolites involved in grapevine response to invasion by esca-associated fungi, eight metabolites were classified in decreasing importance order as thiamine, uric acid, linolenoyl-linolenoyl-glycerol, phenylalanine, N-acetylthreonine, stachydrine, gentisic acid-5-glucoside, and harmane. Levels of thiamine steadily increased with symptom progression from the woods to the leaves, suggesting a biological function for thiamine as a plant defense activation agent. Levels of uric acid declined with increasing symptom severity, as were the levels of the diacylglycerolipid linolenoyl-linolenoyl-glycerol, and the amino acids phenylalanine and N-acetylthreonine. Depressed levels of these amino acids were in accordance with the accumulation of the alkaloid harmane and the hydroxybenzoate gentisic acid-5-glucoside. Monitoring of these metabolites in grapevine leaves could assist in detecting plant stress before visible signs are present. Overall, these data provide a better understanding of the role of metabolites in the host-pathogen relationships.