Characterization of a bZIP transcription factor that regulates the phenylpropanoid pathway in grapevine

In grapevine (Vitis vinifera L.) flavonoids accumulate preferentially in the skin and seeds of grapes (Downey et al. 2004) determining the colour but also the final flavour and astringency of red and white wines. Furthermore, flavonoids extracted from grape berries and seeds exhibit strong nutraceutical potential with a broad spectrum of pharmacological and therapeutic effects (Nassiri-Asl and Hosseinzadeh 2009). Although the general flavonoid pathway has been genetically and biochemically elucidated in many plant species and most recently also in grapevine (Hichri et al. 2011), its regulation still remains not completely characterized. In this study we report the characterization of a grapevine bZIP transcription factor involved in flavonoid biosynthesis regulation. According to the ten-classes classification proposed in Arabidopsis, this VvbZIP belongs to the S-group of bZIP. Its expression along fruit development is higher at the flowering stage and is induced by UV-B treatment. The overexpression of VvbZIP in tobacco transgenic lines positively correlates with the flower content of quercetin and cyanidin in the glycosilated form. Furthermore, transient expression assays by bombardment of grapevine suspension cultures, have revealed that VvbZIP activates the flavonoid pathway at different sites and through the interaction with other co-factors.