Theanine transporters identified in tea plants (Camellia sinensis L.).

Abstract

Theanine, a unique non-proteinogenic amino acid, is an important component of tea, as it confers the umami taste and relaxation effect of tea as a beverage. Theanine is primarily synthesized in tea roots and is subsequently transported to young shoots, which are harvested for tea production. Currently, the mechanism for theanine transport in the tea plant remains unknown. Here, by screening a yeast mutant library, followed by functional analyses, we identified the glutamine permease, GNP1 as a specific transporter for theanine in yeast. Although there is no GNP1 homolog in the tea plant, we assessed the theanine transport ability of 9 tea plant Amino Acid Permease (AAP) family members, with six exhibiting transport activity. We further determined that CsAAP1, CsAAP2, CsAAP4, CsAAP5, CsAAP6 and CsAAP8 exhibited moderate theanine affinities and transport was H+ -dependent. The tissue-specific expression of these 6 CsAAPs in leaves, vascular tissues, and the root suggested their broad roles in theanine loading and unloading from the vascular system, and in targeting to sink tissues. Furthermore, expression of these CsAAPs was shown to be seasonally regulated, coincident with theanine transport within the tea plant. Finally, CsAAP1 expression in the root was highly correlated with root-to-bud transport of theanine, in 7 tea plant cultivars. Taken together, these findings support the hypothesis that members of the CsAAP family transport theanine and participate in its root-to-shoot delivery in the tea plant. This article is protected by copyright. All rights reserved.