Integrated transcriptomics and metabolomics analysis of catechins, caffeine and theanine biosynthesis in tea plant (Camellia sinensis) over the course of seasons

Abstract

Background: Catechins, caffeine, and theanine as three important metabolites in the tea leaves play essential roles in the formation of specific taste and shows potential health benefits to humans. However, the knowledge on the dynamic changes of these metabolites content over seasons, as well as the candidate regulatory factors, remains largely undetermined.

Results: An integrated transcriptomic and metabolomic approach was used to analyze the dynamic changes of three mainly metabolites including catechins, caffeine, and theanine, and to explore the potential influencing factors associated with these dynamic changes over the course of seasons. We found that the catechins abundance was higher in Summer than that in Spring and Autumn, and the theanine abundance was significantly higher in Spring than that in Summer and Autumn, whereas caffeine exhibited no significant changes over three seasons. Transcriptomics analysis suggested that genes in photosynthesis pathway were significantly down-regulated which might in linkage to the formation of different phenotypes and metabolites content in the tea leaves of varied seasons. Fifty-six copies of nine genes in catechins biosynthesis, 30 copies of 10 genes in caffeine biosynthesis, and 12 copies of six genes in theanine biosynthesis were detected. The correlative analysis further presented that eight genes can be regulated by transcription factors, and highly correlated with the changes of metabolites abundance in tea-leaves.

Conclusion: Sunshine intensity as a key factor can affect photosynthesis of tea plants, further affect the expression of major Transcription factors (TFs) and structural genes in, and finally resulted in the various amounts of catechins, caffeine and theaine in tea-leaves over three seasons. These findings provide new insights into abundance and influencing factors of metabolites of tea in different seasons, and further our understanding in the formation of flavor, nutrition and medicinal function.

Keywords: Caffeine; Catechins; Metabolomics; Seasons; Theanine; Transcriptomics.

Fig. 1

Phenotype analysis and systematic analysis of transcriptome and metabolome data of tea samples in different seasons. a Phenotype of tea samples collected from different season, b c. Correlation heatmaps of data in metabolome and transcriptome respectively. d, e. Principal component analysis of data obtained in metabolome and transcriptome respectively. The explained variances are shown in brackets. Spr: Spring; Sum: Summer; Aut: Autumn. Bar = 15 mm

Fig. 2

Statistical analysis of up and down regulated genes of in transcriptome. The pairwise comparisons between three samples were conducted including Summer vs Spring, Autumn vs Summer, Autumn vs Spring. All up (down) regulated genes with significant differences were collected and analyze in GO and KEGG database. a, b. Venn diagram analysis of up and down regulated union gene, respectively. c, d KEGG enrichment analysis of up and down regulated union genes, respectively. e, f Go enrichment analysis of up and down regulated genes, respectively. Spr: Spring; Sum: Summer; Aut: Autumn

Fig. 3

Validation of the relative expression levels of DEGs by qRT-PCR. Histogram graph means the data in transcriptome analysis, and line indicates the data of qRT-PCR

Fig. 4

Gene expression, catechins content and the correlations between them in three different seasons. a. The biosynthesis pathway of catechins in tea plants. b. The concentration of each catechin in tea leaves of three seasons. c Heat map of detected genes in catechins biosynthesis pathway of transcriptome data. The correlation between b and c were indicated with straight lines (coefficients> 0.9, P < 0.05). Full line means positive correlation, dotted line means negative correlation. ANR: anthocyanidin reductase; ANS: anthocyanidin synthase; CHS: chalcone synthase; CHI: chalcone isomerase; DFR: dihydroflavonol 4-reductase; F3’H: flavanone 3-hydroxylase; F3’5’H: flavonoid 3′,5′-hydroxylase; SCPL1A: type 1A serine carboxypeptidase-like acyltransferases

Fig. 5

Gene expression, caffeine content and the correlations between them in three different seasons. a. The biosynthesis pathway of caffeine in tea plants. b The concentration of caffeine in tea leaves of three seasons. c Heat map of detected genes in caffeine biosynthesis pathway of transcriptome data. The correlation between b and c were indicated with straight lines (coefficients> 0.9, P < 0.05). Full line means positive correlation, dotted line indicates negative correlation. 5′-NT: 5′-nucleotidase; AMPD: AMP deaminase; APRT: adenine phosphoribosyltransferase; GDA: guanine deaminase; GMPS: GMP synthase; IMPDH: IMP dehydrogenase; NMT: N-methyltransferase; SAMS: S-adenosyl-L-methionine; TCS: caffeine synthase

Fig. 6

Gene expression, theanine content and the correlations between them in three different seasons. a. The biosynthesis pathway of theanine in tea plants. b The concentration of theanine in tea leaves of three seasons. c Heat map of detected genes in theanine biosynthesis pathway of transcriptome data. The correlation between b and c were indicated with straight lines (coefficients> 0.9, P < 0.05). Full line means positive correlation, dotted line indicates negative correlation. TS: theanine synthetase; GS: glutamine synthetase; GOGAT: glutamate synthase; GDH: glutamate dehydrogenase; SAMDC: S-adenosylmethionine decarboxylase; ADC: arginine decarboxylase

Fig. 7

Transcription factor regulation networks on catechins, caffeine, theanine gene expression and metabolite biosynthesis. The genes related with the expression of TFs were listed in the middle cycle, and red line means positive correlation, blue line means negative correlation between compound content and gene expression. EC: (−)-epicatechin; GC: (+)-gallocatechin; EGC: (−)-epigallocatechin; EGCG: (−)-epigallocatechin-3-gallate; ECG: (−)-epicatechin-3-gallate