Transcriptional regulation of amino acid metabolism in response to nitrogen deficiency and nitrogen forms in tea plant root (Camellia sinensis L.)

Abstract

Free amino acids, including theanine, glutamine and glutamate, contribute greatly to the pleasant taste and multiple health benefits of tea. Amino acids in tea plants are mainly synthesized in roots and transported to new shoots, which are significantly affected by nitrogen (N) level and forms. However, the regulatory amino acid metabolism genes have not been systemically identified in tea plants. Here, we investigated the dynamic changes of free amino acid contents in response to N deficiency and forms in tea plant roots, and systemically identified the genes associated amino acid contents in individual metabolism pathways. Our results showed that glutamate-derived amino acids are the most dynamic in response to various forms of N and N deficiency. We then performed transcriptomic analyses of roots treated with N deficiency and various forms of N, and differentially expressed amino acid metabolic genes in each pathway were identified. The analyses on expression patterns and transcriptional responses of metabolic genes to N treatments provided novel insights for the molecular basis of high accumulation of theanine in tea plant root. These analyses also identified potential regulatory genes in dynamic amino acid metabolism in tea plant root. Furthermore, our findings indicated that the dynamic expression levels of CsGDH, CsAlaDC, CsAspAT, CsSDH, CsPAL, CsSHMT were highly correlated with changes of amino acid contents in their corresponding pathways. Herein, this study provides comprehensive insights into transcriptional regulation of amino acid metabolism in response to nitrogen deficiency and nitrogen forms in tea plant root.(Ser), glycine (Gly) and cysteine (Cys) synthesis. In tea plant, Thea is synthesized from Glu and ethylamine (EA) by theanine synthetase (TS) 14 . EA is likely produced from alanine under the catalysis of alanine decarboxylase 15 .Amino acid catabolism have been clearly described in animals, however, limited information of amino acid catabolism is available in plants. Hildebrandt et al. summarized the catabolic pathways of amino acids in land plants. Generally, amino acids are catabolized by oxidative deamination, oxidative decarboxylation, and transamination. These reactions are catalyzed by amino acid dehydrolases, decarboxylases and aminotransferases, respectively. Gln, Asn and Arg are also hydrolyzed by asparaginase, glutaminase, and arginase to release amide groups 16 .The accumulation of free amino acids is resultant of biosynthesis and catabolism. Previous studies showed that feedback inhibition loops control amino acid biosynthesis in plants 17 . Here, the accumulation of an amino acid inhibits the transcription or the activities of the enzymes in its biosynthesis pathway [18][19][20] . Expression of feedback-insensitive form of enzymes resulted in higher levels of the corresponding amino acids 17,21 . The central role of amino acid catabolism is to adjust the amino acid pool size, especially under stress conditions 12 . Some regulatory enzymes in amino acid metabolism have been ident...

Effects of Long-Term Nitrogen Fertilization on the Formation of Metabolites Related to Tea Quality in Subtropical China

“…AAATs catalyze l - phenylalanine into phenylpyruvic acid in tea plants, and CsAAAT2 was proposed as the key one [ 28 ]. The expression of CsPAL and CsAAAT2 under long-term N fertilization was significantly lower than that with no N fertilization ( Figure 5 B), consistent with previous studies on the effect of N application on tea plants using RNA-Seq [ 13 , 19 , 59 ]. From the above results, we hypothesized that, on the one hand, as a result of long-term N application, the accumulation of chlorophyll in tea leaves increased and more carbon-containing compounds were used to synthesize amino acids, while the concentration of substrate for the synthesis of polyphenols was relatively reduced, which led to the reduction in the content of catechins; on the other hand, the down-regulation of CsPAL and CsAAAT2 involved in the l -phenylalanine pathway might be the main factor leading to the decrease of these metabolites in this pathway.…”

“…N application can improve the nutrient supply from the soil, thereby preserving the normal physiological metabolism of tea plants, which is very important for maintaining tea quality and yield [ 13 ]. According to official statistics, high N application cultivation is universal in tea plantations in China; the national average application is 491 kg/hm 2 N per year [ 14 ].…”

Genome-Wide Identification of Seven Polyamine Oxidase Genes in Camellia sinensis (L.) and Their Expression Patterns Under Various Abiotic Stresses

“…Transcriptome data of nitrogen nutritional stress in the CsPAO gene family were published by our laboratory (Yang et al, 2020). In the control group, tea seedlings were hydroponically cultured with Shigeki Konishi nutrient solution.…”

The effects of different types of mulch on soil properties and tea production and quality

“…wileyonlinelibrary.com/jsfa NH 4 + , 45 thus the application of nitrogen fertilizers and organic matter (urea) has also been practiced in tea plantations. 46,47 A recent study reported that organic fertilizer significantly increased the amino acid content of tea.…”

“…The availability of nutrients is highly associated with tea plants productivity and quality 44 . Tea plants preferentially assimilate NH 4 + , 45 thus the application of nitrogen fertilizers and organic matter (urea) has also been practiced in tea plantations 46,47 . A recent study reported that organic fertilizer significantly increased the amino acid content of tea 48 .…”