Identification and characterization of early pathway genes of ellagitannin biosynthesis in strawberry (F. vesca)

Ellagitannins are polyphenolic antioxidants found in certain fruits, trees, tea and medicinal plants. They are a subclass of hydrolyzable tannins and derived from 3-dehydroshikimate (DHS), an intermediate of the shikimate pathway. In many fruits such as strawberries, raspberries, blackberries or pomegranate, ellagitannins, besides anthocyanins, are the most abundant antioxidants. The high amount of antioxidants present in these fruits have been associated with a reduced risk of cardiovascular disease, Diabetes mellitus (type 2) or cancer and these properties, together with the pleasant taste, have made berries one of the favorite fruits on the fresh food market but also as source for nutraceuticals or functional foods. Due to the previously described bioactivities associated with ellagitannins, studies at the molecular level and identification of genes involved in this biosynthetic pathway are mandatory for further engineering strategies in planta to modulate the amount of metabolites (transgenic strawberry; breeding programmes). But also studies in microbial system are necessary to establish more efficient production of these valuable compounds. The identification and characterization of four putative shikimate dehydrogenase encoding genes, which catalyze the first step during ellagitannin biosynthesis leading to the production of gallic acid is ongoing in strawberry and raspberry. Furthermore, the identification and characterizing of two putative β-glucogallin-dependent galloyl-transferase encoding genes is in progress. These enzymes might catalyze one or several of the galloylation steps later in the pathway, leading to the production of pentagalloylglucose, the precursor of ellagitannins.