Enzyme Catalytic Efficiencies and Relative Gene Expression Levels of ( R )-Linalool Synthase and ( S )-Linalool Synthase Determine the Proportion of Linalool Enantiomers in Camellia sinensis var. sinensis .

Linalool is abundant in tea leaves and contributes greatly to tea aroma. The two isomers of linalool, ( R )-linalool and ( S )-linalool, exist in tea leaves. Our study found that ( R )-linalool was the minor isomer in nine of Camellia sinensis var. sinensis cultivars. The ( R )-linalool synthase of tea plant CsRLIS was identified subsequently. It is a chloroplast-located protein and specifically catalyzes the formation of ( R )-linalool in vitro and in vivo . CsRLIS was observed to be a stress-responsive gene and caused the accumulation of internal ( R )-linalool during oolong tea manufacture, mechanical wounding, and insect attack. Further study demonstrated that the catalytic efficiency of CsRLIS was much lower than that of ( S )-linalool synthase CsSLIS, which might explain the lower ( R )-linalool proportion in C. sinensis var. sinensis cultivars. The relative expression levels of CsRLIS and CsSLIS may also affect the ( R )-linalool proportions among C. sinensis var. sinensis cultivars. This information will help us understand differential distributions of chiral aroma compounds in tea.