Metabolic responses of grapevine leaves to grapevine leafroll-associated virus 3-infection

Abstract

Grapevine leafroll disease, primarily associated with grapevine leafroll-associated virus 3 (GLRaV-3), significantly affects grapevine physiology and productivity. However, its effects on grapevine leaf secondary metabolism remain incompletely understood. This study investigated metabolic responses of grapevine leaves of the Croatian cultivar ‘Plavac mali’ to GLRaV-3 infection by integrating analyses of photosynthetic pigments, oxidative stress markers, phenolic compounds and volatile organic compounds (VOCs). Virus-free and GLRaV-3-infected plants were established under controlled conditions and compared using targeted chromatographic analyses and multivariate statistics.

GLRaV-3 infection significantly reduced chlorophylls and carotenoids, indicating impaired photosynthetic capacity, while hydrogen peroxide, malondialdehyde and proline levels increased, reflecting enhanced oxidative stress. Concomitantly, the phenolic profile of infected leaves revealed a pronounced accumulation of hydroxycinnamic and hydroxybenzoic acids, flavonols and stilbenes, suggesting activation of phenylpropanoid metabolism. In contrast, p-coumaric acid was higher in virus-free leaves, indicating a possible metabolic shift toward downstream defense compounds in infected plants.

VOCs analysis demonstrated strong induction of fatty acid-derived green leaf volatiles, including C6 aldehydes and alcohols, as well as methyl salicylate, a key signal molecule in systemic acquired resistance. Conversely, several benzenoid and carotenoid-derived volatiles were reduced in infected leaves. Principal component analysis clearly separated virus-free and infected samples based on both phenolic and VOC profiles, highlighting a distinct metabolic signature associated with GLRaV-3 infection.

Overall, GLRaV-3 infection induced a coordinated metabolic reprogramming in grapevine leaves characterized by reduced photosynthetic capacity, oxidative stress and enhanced allocation of carbon and redox resources toward defense-related secondary metabolism. The combined phenolic and VOC changes define a characteristic defense-oriented chemical phenotype and identify potential non-invasive biomarkers for the detection and monitoring of grapevine leafroll disease.

These findings contribute to a better understanding of grapevine–virus interactions and provide a biochemical framework for future metabolomics-based diagnostics and resistance-oriented breeding strategies.