Phenylpropanoid biosynthesis and regulation in Solanum melongena cv "Lunga Napoletana"

Delphinidin-3-rutinoside (D3R), and chlorogenic acid (CGA) are the major phenylpropanoids metabolites in eggplant tissues, with CGA constituting over 90% of total phenolics. These metabolites have strong antioxidant properties and confer high nutritional value to eggplant fruits. To gain insight in the CGA and anthocyanin biosynthesis and regulation in eggplant, in this study we performed biochemical analysis to characterize the distribution of phenylpropanoids in different tissues (young and mature leaf, stem, root, flower, fruit skin and flesh) of eggplant cv "Lunga Napoletana" by LC-MS. Parallely we evaluated by qRT-PCR the expression of key structural genes related to phenylpropanoid biosynthesis, i.e PAL, HQT, DFR, ANS. We found a positive correlation between most of the CGA biosynthetic genes and CGA accumulation, as well as between DFR and ANS genes and D3R accumulation in eggplant anthocyanic tissues. In silico analyses of cis acting elements in the promoters of PAL, HQT and ANS revealed the presence of several Myb regulatory elements. Therefore, we isolated putative MYB regulatory genes, and found they are located in a phylogenetic clade strictly close to R2R3-MYB proteins known to be relevant for regulation of anthocyanin and phenolic acids biosynthesis. Two-hybrid assay confirmed interaction with a heterologous bHLH protein, thus supporting the role of the isolated eggplant MYBTF as an activator of the anthocyanin pathway. Moreover functional analysis by transient expression of the isolated MYB in N. tabacum, highlighted that transformed tobacco leaves showed a doubled amount of CGA as well as activation of anthocyanin biosynthesis, Further, since several R2R3-MYBs belonging to the anthocyanin- and phenolic acids-activating class have been identified in many Solanaceae except eggplant, we are currently extending our studies to other MYB TFs in order to understand their regulative role in eggplant.