Theanine transporters are involved in nitrogen deficiency response in tea plant (Camellia sinensis L.)

Nitrogen in soil directly influences the production and quality of tea. However, high nitrogen application in tea plantation leads to soil acidification and environmental pollution. Studies in model plants showed that plasma membrane localized amino acid transporter can regulate the distribution of amino acids to enhance nitrogen use efficiency. Our recent study identified six CsAAPs as transporters for theanine, a unique and most abundant non-proteinaceous amino acid in tea plant. In this work, we found these theanine transporters can also transport Glutamine, Glutamate, aspartate, alanine and γ-aminobutyric acid. Tissue-specific expression analyses showed that CsAAP1, CsAAP5 and CsAAP6 mainly expressed in leaves, CsAAP8 in root, CsAAP4 and CsAAP2 in stem. Furthermore, the expression of these CsAAPs was induced by nitrogen deficiency in a tissue-specific manner. Subcellular localization analyses showed that CsAAP1, CsAAP2 and CsAAP6 location were in the plasma membrane and endoplasmic reticulum. Taken together, these results suggested theanine transporters are involved in nitrogen deficiency response probably by mediating amino acid transport from roots to new shoots and from source to sink tissues in tea plants.