Abstract:To reveal the formation mechanism of fruit flavor in Morinda citrifolia, the activity and expression pattern of fructokinase (FRK) gene during fruit development were studied. The results showed that the contents of fructose, sucrose and glucose in fruit of M. citrifolia accumulated with the development of fruit, and reached the highest when the fruit was fully mature, while the activity of fructokinase decreased with the development of the fruit. The fructokinase gene TRINITY_DN17192_c0_g1, named as McFRK2 was cloned from M. citrifolia fruit, with 984 bp ORF, encoding 327 amino acids, and the GenBank accession number was MW380742. The amino acid sequence of McFRK2 was similar to that of FRK2 of coffee (Coffea arabica) at 98%. By using qRT-PCR, the expression of McFRK2 decreased gradually during fruit development. When the fruit was ripe, the expression of McFRK2 tended to be stable, which was consistent with the change trend of fructokinase activity. Therefore, McFRK2 might be involved in glucose metabolism by regulating fructokinase activity in fruits, which plays an important role in regulating fruit flavor formation.