Abstract
Organic tea is more popular than conventional tea that originates from fertilized plants. Amino acids inorganic soils constitute a substantial pool nitrogen (N) available for plants. However, the amino-acid contents in soils of tea plantations and how tea plants take up these amino acids remain largely unknown. In this study, we show that the amino-acid content in the soil of an organic tea plantation is significantly higher than that of a conventional tea plantation. Glutamate, alanine, valine, and leucine were the most abundant amino acids in the soil of this tea plantation. When 15N-glutamate was fed to tea plants, it was efficiently absorbed and significantly increased the contents of other amino acids in the roots. We cloned seven CsLHT genes encoding amino-acid transporters and found that the expression of CsLHT1, CsLHT2, and CsLHT6 in the roots significantly increased upon glutamate feeding. Moreover, the expression of CsLHT1 or CsLHT6 in a yeast amino-acid uptake-defective mutant, 22∆10α, enabled growth on media with amino acids constituting the sole N source. Amino-acid uptake assays indicated that CsLHT1 and CsLHT6 are H+-dependent high- and low-affinity amino-acid transporters, respectively. We further demonstrated that CsLHT1 and CsLHT6 are highly expressed in the roots and are localized to the plasma membrane. Moreover, overexpression of CsLHT1 and CsLHT6 in Arabidopsis significantly improved the uptake of exogenously supplied 15N-glutamate and 15N-glutamine. Taken together, our findings are consistent with the involvement of CsLHT1 and CsLHT6 in amino-acid uptake from the soil, which is particularly important for tea plants grown inorganic tea plantations.
Highlights
Owing to its pleasant flavor and multiple health benefits, tea is the second most popular nonalcoholic beverage worldwide, second only to water
The total amino-acid content in the soils was 1–8 μg/g dry soil, with the amino-acid contents in the organic tea plantation soil being higher than those in the conventional tea plantation soil (Fig. 1b, c). These results confirmed the presence of amino acids in the soils of tea plantations, which is consistent with findings in other ecosystems, and implied a more important role of soil amino acids inorganic tea plantations
AtLHT1 and AtLHT6, functioning in the uptake of amino acids from the soil in Arabidopsis, are highly expressed in roots[25,37,47]. To assess this relationship for CsLHT1 and CsLHT6, we evaluated their expression in many tea plant tissues, including the leaf buds; first, third and fifth leaves and major veins (MV) (1st leaf and 1st MV; 3rd leaf and 3rd MV; 5th leaf and 5th MV); stems; and vascular bundles extracted from both stem and root tissues (Fig. 7a)
Summary
Owing to its pleasant flavor and multiple health benefits, tea is the second most popular nonalcoholic beverage worldwide, second only to water. Previous studies have shown that the biosynthesis of these metabolites is related to N (N) conditions[1,2,3], with highquality tea being produced from plants grown under adequate N levels[1,4,5]. High N fertilization accelerates soil acidification[6], which can lead to high (e.g., lead and chromium) in tea leaves, posing potential risks to human health[7]. Tea produced from organic plantations has increased in popularity[8,9]. In China, during the past two decades, organic tea production has increased >45-fold[9]
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