Genome-wide association studies reveal the genetic basis of amino acid content variation in tea plants

Tea is one of the most popular non-alcoholic beverages in the world, and free amino acids, especially theanine, make a major contribution to the umami taste of tea. However, the genetic basis of the variation in amino acid content in tea plants remains largely unknown. Here, we measured the free amino acid content in fresh leaves of 174 tea accessions over two years using a targeted metabolomics approach and obtained genotype data via RNA sequencing. Genome-wide association studies were conducted to investigate loci affecting the content of free amino acids. A total of 69 quantitative trait loci (–log10(P-value)>5) were identified. Functional annotation revealed that branched-chain amino acid aminotransferase, glutamine synthetase, nitrate transporter, and glutamate decarboxylase might be important for amino acid metabolism. Two significant loci, glutamine synthetase (Glu1, P=3.71×10–4; Arg1, P=4.61×10–5) and branched-chain amino acid aminotransferase (Val1, P=4.67×10–5; I_Leu1, P=3.56×10–6), were identified, respectively. Based on the genotyping result, two alleles of CsGS (CsGS-L and CsGS-H) and CsBCAT (CsBCAT-L and CsBCAT-H) were selected to perform function verification. Overexpression of CsGS-L and CsGS-H enhanced the contents of glutamate and arginine in transgenic plants, and overexpression of CsBCAT-L and CsBCAT-H promoted the accumulation of valine, isoleucine and leucine. Enzyme activity assay uncovered that SNP1054 is important for CsGS catalyzing glutamate into glutamine. Furthermore, CsGS-L and CsGS-H differentially regulated the accumulation of glutamine, and CsBCAT-L and CsBCAT-H differentially regulated the accumulation of branched-chain amino acids. In summary, the findings in our study would provide new insights into the genetic basis of amino acids contents variation in tea plants and facilitate the identification of elite genes to enhance amino acids content.