Transcriptome and metabolite profiling reveals correlation of smoke taint compounds accumulation in Vitis Vinifera L. berries with phenylpropanoid pathway – the impact of plant growth regulators

Abstract

Wildfire smoke exposure has continued to be a threat for the wine industry, causing smoke tainted wines, reminiscent of medicinal, smoky smell and ashy aftertaste. The major tainted compounds in the smoke have been identified as volatile phenols (VPs) such as guaiacol, cresols, and syringol. Grape berries exposed to smoke can uptake these compounds and metabolize them into glycosylated volatile phenols (Gly-VPs). The glycosides can be hydrolyzed during fermentation, through wine storage, and upon consumption, releasing the tainted flavor. The biosynthetic pathway of Gly-VPs is ill defined, albeit studies have identified several smoke-responsive glycotransferases that contribute to their accumulation. The identified glycotransferases function in the phenylpropanoid pathway and are responsible for other secondary metabolites biosynthesis. Therefore, this study aims to investigate the correlation of Gly-VPs accumulation with monomeric phenolics biosynthesis in Cabernet Sauvignon berries following simulated smoke exposure. Plant growth regulators that are reported to regulate the phenylpropanoid pathway were applied to amplify the potential correlation and to provide insights on possible mitigation practice in the vineyard under smoke exposure risk. Abscisic acid (ABA) and methyl jasmonate (MeJA) were applied to the fruit zone of the vine one week prior to the simulated smoke exposure. The grapes were at E-L stage 36, one-week post-veraison. Grapes were sampled 1-, 5-day post smoke exposure and at harvest (33-day post exposure). There was a positive correlation between the concentration of Gly-VPs and monomeric phenolics in grapes collected at harvest, regardless of the ABA, MeJA application. The ABA treated grapes had significant higher amounts of Gly-VPs than the control without ABA treatment 5-day post exposure. The stimulating impact of ABA on Gly-VPs accumulation diminished for some of the measured Gly-VPs at harvest. The results suggested that either the application of ABA might promote further metabolism of the measured Gly-VPs into new metabolites or it impacted the rate of the glycosylation process rather than the amount. The effect of MeJA on Gly-VPs accumulation was arbitrary. More analyses including transcriptome profiling will be performed to elucidate the observations.