Polyphenol content and differential expression of flavonoid biosynthetic pathway genes in berries of Aglianico

Among the Italian grape cultivars, 'Aglianico del Taburno' is characterized by a high content of proanthocyanidins (PAs), representing a model for astringency. Little is known on PA accumulation in grapevine and their genetic control during berry development. The aim of this work was to monitor the accumulation of the compounds responsible for the astringency during berry ripening of 'Aglianico' and to correlate it with expression of selected PA-pathway key-genes. Berries were collected at five developmental stages [fruit-set, pre-véraison, véraison, Mid-Ripening and Complete Ripening] and dissected in skins and seeds. PAs were extracted and the content of total phenolics, total tannins, flavans and anthocyanins was evaluated. RT-qPCR was carried out to evaluate the expression of few key structural genes of the flavonoid pathway. Our results showed that extracted PAs were more abundant in seeds with respect to skins. Differences in the distribution of each compound during berry ripening were also detected. Regarding gene expression analyses, we found that PA-key-genes displayed different trends in all tissues. We hypothesize that 'Aglianico' is able to accumulate high levels of polyphenols due to its ability to modulate the expression of key genes in a tissue-specific manner.