Phenylpropanoid biosynthesis and regulation in Solanum melongena cvLunga 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, 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 the expression of key structural genes related to phenylpropanoid biosynthesis by qRT-PCR, i.e.PAL, HQT, DFR, ANS. We found a positive correlation between transcription of 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 gene, which is located in a phylogenetic clade strictly close to R2R3-MYB proteins, with a relevant function for regulation of anthocyanin and phenolic acids biosynthesis. Two-hybrid assay confirmed interaction of the isolated eggplant MYBTF with a heterologous bHLH protein, thus supporting its role as an activator of the anthocyanin pathway. Moreover functional analysis by transient expression of the isolated MYB in N. tabacum showed a doubled amount of CGA as well asactivation of anthocyanin biosynthesis intransformed tobacco leaves. 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.