MOLECULAR CHARACTERIZATION OF GENES INVOLVED IN THE PRESENCE OF ANTHOCYANINS IN EGGPLANT (S. MELONGENA L.)

Eggplant (Solanum melongena L.) is a berry-producing vegetable belonging to the large Solanaceae family. Eggplant berries are rich in important secondary metabolites like phenolic compounds (chlorogenic acid in the flesh and anthocyanins in the peel) and flavonols, two classes of antioxidant molecules with suggested health-promoting effects in humans. Anthocyanins pathway is one of most investigated and well characterized pathway among the higher plants. However, the information available for eggplant anthocyanins pathway are rather limited whit the respect to other Solanaceous crop like tomato (S. lycopersicum ) and potato (S. tuberosum). As part of this Ph.D. project, focusing on the highly conserved MYB-bHLH-WD (MBW) transcriptional complex model, which is pivotal in the transcriptional regulation of many anthocyanins related genes, the eggplant MBW were identified and functional characterized. Moreover, a regulatory R3 MYB type repressor (Smel- MYBL1), never reported before, was identified and characterized as well. Fruit peel pigmentation of different varieties of eggplant can vary widely from white to green to purple and violet; in particular, the black/dark purple and dark/light violet peel pigmentations reflect the alternative presence of two different anthocyanins: delfinidine-3-rutinoside (D3R) and delphinidin-3-[p-coumaroylrutinoside]-5- glucoside (nasunin), respectively. The conversion of D3R into nasunin is still an unelucidated part of the anthocyanin pathway in eggplant. The genes responsible of this metabolic step, the SmAAT was identified and functionally characterized through complementation in genotypes carrying the recessive mutant aat allele. Moreover, another genes, Sm5GT1, putatively involved in this step were identified, but more efforts are needed to characterize it. Furthermore, the ripening process is a pivotal aspect which affects the anthocyanins content. The eggplant ripening is commonly divided into three stages: unripe (stage A), commercially ripen (stage B) and physiologically ripen (stage C). Anthocyanin pigments are accumulated to the highest levels at the unripe fruit stage and their levels dramatically decreased as ripening progresses (Mennella et al., 2012), although the total phenolic content remained quite stable (Esteban et al., 1992) leading to the hypothesis that some other still undetermined phenolics are produced during this stage instead of anthocyanins. Focusing on these evidences a list of phenols never reported before in the eggplant peel were identified by HPLC-DAD- UV-VIS analysis. The identification of those new compounds and the recent availability of eggplant genetic resources have allowed the identification of the genes putatively involved in the ripening metabolism of the eggplant berries. The characterization by RT-qPCR three genes were carried out: SmFLS and a couple of SmGT. This genes are now the best candidate for future experiments aimed at irrefutably proving this function.