Isolation and characterization of two hydroperoxide lyase genes from grape berries

C6 compounds are the major fraction of the volatile profiles of grape berries, contributing the typical 'green' aroma to the grape and wine. Hydroperoxide lyase (HPL) catalyzes the cleavage of fatty acid hydroperoxides to produce C6 compounds. Two hypothetical genes, VvHPL1 and VvHPL2 were cloned from grape berries (Vitis vinifera L. Cabernet Sauvignon). Bioinformatics analysis revealed that the proteins encoded by these two genes both belong to subfamily of cytochrome P450 and contain typical conserved domains of HPLs, and have high identity with HPLs from other plants. Prokaryotically-expressed VvHPL1 and VvHPL2 with thioredoxin-6xHis-fusion partner were confirmed to have enzymatic activity. VvHPL1 is specific for 13-HPOD (T) producing C6 aldehydes with relatively higher activity and VvHPL2 catalyzes the cleavage of both 9- and 13-hydroperoxides producing C6 aldehydes and C9 aldehydes respectively. Analysis of real time-PCR showed that VvHPL2 was highly expressed in the leaves and the flowers of the grapes, while relatively low transcript abundance was detected in the berries, tendril and stems; VvHPL1 had high expression in all detected tissues. During grape berry development, the expression of these two isogenes presented similar trends with a rapid increase after veraison and a decrease at full-ripen stage, which roughly corresponded to the accumulation of their volatile products. These data lay an essential foundation for further study on the accumulation and control of C6 volatiles in grape berries.