Integrated Transcriptome and Metabolic Analyses Reveals Novel Insights into Free Amino Acid Metabolism in Huangjinya Tea Cultivar

Abstract

The chlorotic tea variety Huangjinya, a natural mutant, contains enhanced levels of free amino acids in its leaves, which improves the drinking quality of its brewed tea. Consequently, this chlorotic mutant has a higher economic value than the non-chlorotic varieties. However, the molecular mechanisms behind the increased levels of free amino acids in this mutant are mostly unknown, as are the possible effects of this mutation on the overall metabolome and biosynthetic pathways in tea leaves. To gain further insight into the effects of chlorosis on the global metabolome and biosynthetic pathways in this mutant, Huangjinya plants were grown under normal and reduced sunlight, resulting in chlorotic and non-chlorotic leaves, respectively; their leaves were analyzed using transcriptomics as well as targeted and untargeted metabolomics. Approximately 5,000 genes (8.5% of the total analyzed) and ca. 300 metabolites (14.5% of the total detected) were significantly differentially regulated, thus indicating the occurrence of marked effects of light on the biosynthetic pathways in this mutant plant. Considering primary metabolism, including that of sugars, amino acids, and organic acids, significant changes were observed in the expression of genes involved in both nitrogen (N) and carbon metabolism. The suite of changes not only generated an increase in amino acids, including glutamic acid, glutamine, and theanine, but it also elevated the levels of free ammonium, citrate, and α-ketoglutarate, and lowered the levels of mono- and di-saccharides and of caffeine as compared with the non-chlorotic leaves. Taken together, our results suggest that the increased levels of amino acids in the chlorotic vs. non-chlorotic leaves are likely due to increased protein catabolism and/or decreased glycolysis and diminished biosynthesis of nitrogen-containing compounds other than amino acids, including chlorophyll, purines, nucleotides, and alkaloids.

Widely Targeted Metabolomic and Transcriptomic Analyses of a Novel Albino Tea Mutant of “Rougui”

“…Amino acids and their derivatives are the most studied compounds in albino tea. Consistent with previous studies [12,60], the levels of 20 amino acids and their derivatives were increased markedly in YR, affecting the umami taste and aroma of tea infusions [61]. Conjoint analysis of DEGs and SCMs (Table 3) showed that glutathione on the glutathione metabolic pathway, an α-amino acid that protects cells from oxidation [62], was increased 3.21-fold in YR, whereas the expression of GST was upregulated 2.23-fold.…”

Comparative analysis of primary metabolites and transcriptome changes between ungrafted and pumpkin-grafted watermelon during fruit development

“…Plants use glutamic acid as a nitrogen source for the biosynthesis of nitrogenous compounds. Similar results were reported by Hammond-Kosack & Jones 2000and Zhang, Liu & Ruan (2017).…”

Metabolite signatures of diverse Camellia sinensis tea populations

“…During green tea processing, major catechins from young leaves of C. sinensis remain unoxidized. It is generally believed that a lower ratio of total polyphenols to amino acids in fresh leaves is essential to balance the astringent and the mellow tastes, and hence a prerequisite for producing premium green teas 57 , 58 . Oolong tea accessions are enriched with two methylated catechins and complex kaempferol/quercetin glycoside derivatives acylated with a coumaroyl group.…”