Light Intensity Modulates the Effect of Phosphate Limitation on Carbohydrates, Amino Acids, and Catechins in Tea Plants (Camellia sinensis L.)

Abstract

Metabolites are major contributors to the quality of tea that are regulated by various abiotic stresses. Light intensity and phosphorus (P) supply affect the metabolism of tea plants. However, how these two factors interact and mediate the metabolite levels in tea plants are not fully understood. The present study investigated the consequences of different light intensity and P regimes on the metabolism of carbohydrates, amino acids, and flavonoids in the Fengqing tea cultivar. The leaves and young shoots were subjected to untargeted metabolomics analysis by two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF/MS), ultra-performance liquid chromatography-quadrupole-TOF/MS (UPLC-Q-TOF/MS), and targeted analysis by high-performance liquid chromatography (HPLC) along with quantification of gene expression by quantitative real time-PCR (qRT-PCR). The results from young shoots showed that amino acids, pentose phosphate, and flavonol glycosides pathways were enhanced in response to decreasing light intensities and P deficiency. The expression of the genes hexokinase 1, ribose 5-phosphate isomerase A (RPIA), glutamate synthetase 1 (GS1), prolyl 4-hydroxylase (P4H), and arginase was induced by P limitation, thereafter affecting carbohydrates and amino acids metabolism, where shading modulated the responses of transcripts and corresponding metabolites caused by P deficiency. P deprivation repressed the expression of Pi transport, stress, sensing, and signaling (SPX2) and induced bidirectional sugar transporter (SWEET3) and amino acid permeases (AAP) which ultimately caused an increase in the amino acids: glutamate (Glu), proline (Pro), and arginine (Arg) under shading but decreased catechins [epicatechingallate (ECG) and Gallic acid, GA] content in young shoots.

Keywords: Camellia sinensis L; gene expression; interaction; light intensity; metabolic pathway; phosphorus.

Figure 1

Overview of enriched pathways (A) and pathway impact (B) in young shoots of Fengqing cultivar exposed to different light intensities and Phosphorous (P) levels.

Figure 2

The light and P interactive effect on the biosynthesis of carbohydrates and/or related anaplerotic pathway metabolites to carbohydrates in young shoots of Fengqing cultivar measured by two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOF/MS). The mean of each metabolite followed by a different letter in the heatmap table indicates a significant difference. In the heatmap, red boxes represent the value >1 and are separated into dark red and mild red by the mean value of the figured pathway data (>1) and subsequently <1 with blue color and mean value separated into mild blue and dark blue from figured pathway data (<1). The yellow box represents the normalization value. The blank table in the legend shows the position of the mean P and light treatment value of the metabolites.

Figure 3

The interactive effect of light and P on the biosynthesis of amino acids and/or related anaplerotic pathway metabolites in young shoots of Fengqing cultivar measured by GC×GC–TOF/MS. The mean of each metabolite followed by a different letter in the heatmap table indicates a significant change in light and P treatments. In the heatmap, red boxes represent the value >1 and are separated into dark red and mild red by the mean value of the figured pathway data (>1) and subsequently <1 with blue and mean value separated into mild blue and dark blue from figured pathway data (<1). The yellow box represents the normalization value. The blank table in the legend shows the position of the mean P and light treatment value of the metabolites.

Figure 4

The interactive effects of light and P on the biosynthesis of flavonoids and/or related anaplerotic pathway metabolites of flavonoids in young shoots of Fengqing cultivar measured by ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC–Q–TOF/MS). The mean of each metabolite followed by a different letter in the heatmap table indicates significant change due to light and P treatments. In the heatmap, red boxes represent the value >1 and are separated into dark red and mild red by the mean value of the figured pathway data (>1) and subsequently <1 with blue color and mean value separated into mild blue and dark blue from figured pathway data (<1). The yellow box represents the normalization value. The blank table in the legend shows the position of the mean P and light treatment value of the metabolites.

Figure 5

The bi–plot correlation of young shoots (A) and leaves (B) and the mean concentration of amino acids (C–I) and catechins (J,K) in young shoots. A single bi–plot for the dataset combines both samples and treatments to the principal components; Dim1, dimension 1, and Dim2, dimension 2. Asterisks indicate significant differences: ***is 0.001, **is 0.01, and *is 0.05, ns, non-significant differences, between light and P interaction.

Figure 6

qRT–PCR analyzed (normalized with reference gene delta CT) transporter gene transcripts normalized relative expression in response to full light with +P. Asterisks indicate significant differences: ***is 0.001, ** is 0.01, and *is 0.05, ns, non-significant differences, between light and P interaction.

Figure 7

Linear regression correlation between gene expression under different P levels (A,B) and light regimes (C–E). High P (A), low P (B), full light (FL) (C), medium light (ML) (D), and low light (LL) (E) correlation of gene expression under different P levels and light intensities of Pi transport, stress, and signaling (SPX2), bidirectional sugar transporter 3 (SWEET3), amino acid permeases (AAP), and glutathione S-transferase b (GSTb) in young shoots.

Figure 8

(A,B) Heatmap correlation between P and genes under different P levels and light intensities.

Figure 9

(A,B) Circular representation of the correlation between genes under different P levels and light intensities.