Behavior of 3-isobutyl-2-methoxypyrazine biosynthesis related to proposed precursor and intermediate in wine grape

Although 3-alkyl-2-methoxypyrazines (MPs) are very important flavor compounds in grape and wine, the metabolic pathway of these compounds has not been fully elucidated, and only a few studies have focused on it to date. In this study, we performed in situ incorporation of the proposed precursor (l-Leu) and the key intermediate (2-amino-4-methylpentanamide; AMPA) of 3-isobutyl-2-methoxypyrazine (IBMP) biosynthesis into Cabernet Sauvignon clusters. The IBMP content and the expression levels of key related genes were monitored. IBMP content decreased shortly after l-Leu or AMPA treatment, but subsequently increased significantly, with raised levels of O-methyltransferase genes (VvOMT1 and VvOMT3) in the berries between veraison and maturation. We speculate that l-Leu may be a precursor of IBMP biosynthesis and that AMPA may be a key intermediate.