The pathway to red: anthocyanin biosynthesis in raspberries.

Raspberries are highly appreciated for their unique flavor and bright colors. Therefore, fruit pigmentation is one of the most important quality traits and berries with variation in color that range from deep purple to yellow are available, depending on anthocyanin composition. The leading pathway is genetically determined by several structural and regulatory genes1, some of which were characterized at molecular level2 but none from enzymatic point of view in raspberries. The polyphenol composition of raspberries consists mainly on ellagitannins, followed by anthocyanins (in red raspberries) with smaller amounts of hydroxycinnamic acids, flavonols, flavan-3-ols and proanthocyanidins3. Yellow forms obviously lack anthocyanidins, and some yellow varieties where reported to lack also flavonols4. Apart from the lack of anthocyanins, previous reports didn’t show other significant differences in the polyphenol compositions and antioxidant protection ability of yellow raspberries, which seems to indicate a deviation of secondary metabolism into other directions. In this work, the differences in raspberry fruit pigmentation where studied by transcriptional and analytical approaches. The differential transcriptional profiles of genes of flavonoid biosynthetic pathway (CHS, CHI, F3H, DFR, UFGT, LAR, FHT, ANS and ANR) were analyzed in raspberry varieties with different colors by qRT-PCR. The results taken from the transcriptional profile where combined with the polyphenolic profile of the fruits obtained by reversed phase LC-MS. The combination of these data allowed gaining further knowledge on the biosynthetic pathway to anthocyanins in different raspberry genotypes and colour mutants.