L-Theanine Content and Related Gene Expression: Novel Insights into Theanine Biosynthesis and Hydrolysis among Different Tea Plant (Camellia sinensis L.) Tissues and Cultivars

Abstract

L-Theanine content has tissues and cultivars specificity in tea plant (Camellia sinensis L.), the correlations of theanine metabolic related genes expression profiles with theanine contents were explored in this study. L-theanine contents in the bud and 1st leaf, 2nd leaf, 3rd leaf, old leaf, stem, and lateral root were determined by HPLC from three C. sinensis cultivars, namely ‘Huangjinya’, ‘Anjibaicha’, and ‘Yingshuang’, respectively. The theanine contents in leaves and root of ‘Huangjinya’ were the highest, followed by ‘Anjibaicha’, and ‘Yingshuang’. The theanine contents in the leaves reduced as the leaf mature gradually, and in stem were the least. Seventeen genes encoding enzymes involved in theanine metabolism were identified from GenBank and our tea transcriptome database, including CsTS1, CsTS2, CsGS1, CsGS2, CsGOGAT-Fe, CsGOGAT-NAD(P)H, CsGDH1, CsGDH2, CsALT, CsSAMDC, CsADC, CsCuAO, CsPAO, CsNiR, CsNR, CsGGT1, and CsGGT3. The transcript profiles of those seventeen genes in the different tissues of three tea plant cultivars were analyzed comparatively. Among the different cultivars, the transcript levels of most selected genes in ‘Huangjinya’ were significantly higher than that in the ‘Anjibaicha’ and ‘Yingshuang’. Among the different tissues, the transcript levels of CsTS2, CsGS1, and CsGDH2 almost showed positive correlation with the theanine contents, while the other genes showed negative correlation with the theanine contents in most cases. The theanine contents showed correlations with related genes expression levels among cultivars and tissues of tea plant, and were determined by the integrated effect of the metabolic related genes.

Brassinosteroids Attenuate Moderate High Temperature-Caused Decline in Tea Quality by Enhancing Theanine Biosynthesis in Camellia sinensis L.

“…Afterward, no further decline in theanine content was noticed, indicating a potential acclimation response to the SHT. Theanine accumulation in tea leaves depends on its synthesis, transportation and hydrolysis ( Deng et al, 2008 , 2010 ; Liu et al, 2017b ). Importantly, hydrolysis appears to be minor determinant under perturbed temperatures as SHTs suppress enzyme activity and genes involved in theanine biosynthesis ( Figures 5 , 6 ).…”

“…L -theanine can be detected in almost all tissues in tea plants, however, major site of in planta synthesis is root, from where theanine is transported to the shoot ( Deng et al, 2008 ). Theanine content is high in young leaves and declines with leaf maturity ( Liu et al, 2017b ). There are seventeen genes encoding enzymes involved in theanine metabolism, however, only several genes, including THEANINE SYNTHASE ( CsTS ), have positive correlation with theanine content in tea leaves ( Liu et al, 2017b ).…”

“…Theanine content is high in young leaves and declines with leaf maturity ( Liu et al, 2017b ). There are seventeen genes encoding enzymes involved in theanine metabolism, however, only several genes, including THEANINE SYNTHASE ( CsTS ), have positive correlation with theanine content in tea leaves ( Liu et al, 2017b ). In the theanine biosynthetic pathway, glutamic acid and ethylamine act as the immediate precursors of theanine, which are converted to L -theanine by the catalysis of TS ( Cheng et al, 2017 ).…”

“…Seasonal studies show that tea grown in warmer climate, (e.g., summer tea) are bitter, which is well correlated to high polyphenol and low theanine contents ( Xu et al, 2012 ). Spring tea (tea harvested in cool months) has the highest theanine content, which declines as the weather becomes warmer, indicating that high temperatures negatively impact theanine content in tea ( Liu et al, 2017b ). Due to more bitterness and astringency in summer and autumn teas, their economic values are low.…”

Transcriptome-Wide Analysis of Nitrogen-Regulated Genes in Tea Plant (Camellia sinensis L. O. Kuntze) and Characterization of Amino Acid Transporter CsCAT9.1

“…The higher expression of TEA028194/ CsGS2.1 in shoots than in roots might indicate it plays a role in chloroplasts, together with two other GS isoforms, TEA032217/ CsGS1.1 and TEA015580/ CsGS1.3 . The sequence of GS was highly similar to theanine synthetase (TS) [ 24 , 50 ]. TEA015198/ CsNodulinGS was expressed specifically in the roots and biosynthesis of theanine has been shown to mostly occur in roots [ 32 ].…”