Tonoplast-Localized Theanine Transporter CsCAT2 May Mediate Theanine Storage in the Root of Tea Plants (Camellia sinensis L.).

Lin Feng,Lin Feng,Zhaoliang Zhang,Tianyuan Yang,Shijia Lin,Xiaochun Wan,Yongchao Yu,Jun Sun,Pengcheng Zheng,Linlin Liu,Qi Chen

doi:10.3389/fpls.2021.797854

Abstract

Theanine is the component endowing tea infusion with “umami” taste and antidepression benefits. Theanine is primarily synthesized and stored in root in winter and is transported via vascular tissues to the new shoot in spring. However, the mechanism underlying theanine storage in the root of tea plants remains largely unknown. Cationic amino acid transporter 2 (CsCAT2) in tea plants is homologous to glutamine permease 1 (GNP1), the specific glutamine transporter in yeast. In this study, we identified CsCAT2 as an H+-dependent theanine transporter with medium affinity for theanine. The result of subcellular localization showed that CsCAT2 was a tonoplast-localized transporter. Importantly, CsCAT2 highly expressed in the root in winter during theanine storage and reduced its expression in the root during theanine transport from root-to-shoot in spring. In addition, CsCAT2 expression in the roots of 5 varieties at four time points during December and April was significant negatively correlated with the capacity of theanine root-to-shoot movement. Taken together, these results suggested that CsCAT2 may mediate theanine storage in the vacuole of root cells and may negatively modulate theanine transport from root to shoot.

Highlights

Tea plant (Camellia sinensis L.) is a perennial and commercially valuable crop; its buds and one or two leaves below the bud are harvested for green tea manufacturing
TEA025016.1 is highly homologous to AtCAT2 (Figure 1B), a tonoplast-localized acid transporters (AATs) in Arabidopsis
As described (Figure 2), CsCAT2 expression in the root showed an opposite trend with the process of theanine transport from root to shoot, at four time points (December 1, March 1, March 23, and April 13), in a tea plant cultivar “Shuchazao.” To further illustrate that CsCAT2 plays a role in theanine transport from root to shoot seasonally, we examined CsCAT2 expression in the roots of five cultivars and analyzed the correlation between CsCAT2 expression and the efficiency of theanine root-to-shoot transport

Summary

Introduction

Tea plant (Camellia sinensis L.) is a perennial and commercially valuable crop; its buds and one or two leaves below the bud are harvested for green tea manufacturing. The composition and content of amino acids in the tender shoot leaves are the critical components that endow tea with its flavor and health benefits (Wan, 2003; Hunt et al, 2010; Wan and Xia, 2015). Most amino acids contribute to the umami taste and alleviate the bitterness and astringency of tea infusions. The ratio of amino acids to polyphenols determines the quality and suitability of tea (Wan, 2003). In the tender tea leaves, theanine accounts for more than 50% of the free amino acid content, which significantly correlates with the quality and price of green teas (Yamaguchi and Ninomiya, 2000; Wan, 2003; Feng et al, 2014).

Methods

Results

Conclusion