The origin of the particular aroma of noble rot wines: various fungi contribute to the development of the aroma profile of botrytised grape berries

During noble rot (NR), B. cinerea, together with other filamentous fungi and yeasts, play a role in developing the unique aromatic profile of botrytised wines. To gain more insight into the latter, we generated metatranscriptomic data representing the four NR stages (I-IV) from the Tokaj wine region of Hungary over three months. Since previous research has indicated that the most prevalent filamentous fungi and yeast include Alternaria alternata, Botrytis cinerea, Epicoccum nigrum, Aureobasidium pullulans and Rhodotorula graminis, RNAseq reads were aligned to the latter species. A weighted gene co-expression network analysis (WGCNA) followed by a non-metric multidimensional scaling (NMDS), eigengene ANOVA and enrichment analyses were performed. Amongst the ten generated gene module clusters, enriched pathways involved in synthesising aromatic compounds such as amino acid-, carbohydrate- and lipid metabolism co-jointly expressed by all filamentous fungi and yeast were identified within the turquoise module. Furthermore, it was found that the enzymes involved in the synthesis of aromatic compounds are expressed and up-regulated during the later stages (III-IV) of the NR process. This study has indicated that the unique aromatic profile of botrytised wines is due to the contributions of filamentous fungi and yeasts belonging to the NR grape microbiome, with the main aromatic contributions occurring during the later NR stages.