Effects of Light Intensity on Physiological Characteristics and Expression of Genes in Coumarin Biosynthetic Pathway of Angelica dahurica

Abstract

Plants are affected by changes in light and adaptation mechanisms can affect secondary metabolite synthesis. In this study, the physiological response and regulation of the coumarin biosynthetic pathway of Angelica dahurica to different light intensities (natural light (CK), shade rate 50% (L1), shade rate 70% (L2), and shade rate 90% (L3)) were examined. The chlorophyll content, level of the enzymes of the antioxidant system, extent of lipid peroxidation, and concentrations of the osmoregulatory solute levels were determined in potted plants. Root transcriptome under different light intensities was sequenced using high-throughput technology, and differentially expressed genes (DEGs) related to coumarin biosynthesis were analyzed by quantitative real-time PCR (qRT-PCR). With increasing shade, Chl a, Chl b, Chl a + b, and Chl a/b content increased, while the Chl a/b ratio decreased. The antioxidant enzyme system activity and extent of membrane lipid peroxidation increased. The soluble protein (SP) and proline (Pro) content decreased with the reduction in the light intensity, and soluble sugar (SS) content was found to be highest at 50% shade. The RNA-seq analysis showed that 9388 genes were differentially expressed in the L3 group (7561 were upregulated and 1827 were downregulated). In both the L1 and L2 groups, DEGs were significantly enriched in "Ribosome biosynthesis"; meanwhile, in the L3 group, the DEGs were significantly enriched in "Amino and ribonucleotide sugar metabolism" in KEGG metabolic pathway analysis. Additionally, 4CL (TRINITY_DN40230_c0_g2) and COMT (TRINITY_DN21272_c0_g1) of the phenylpropanoid metabolic pathway were significantly downregulated in the L3 group. In conclusion, A. dahurica grew best under 50% shade and the secondary-metabolite coumarin biosynthetic pathway was inhibited by 90% shade, affecting the yield and quality of medicinal compounds.

Keywords: Angelica dahurica; coumarin biosynthesis; gene expression; light intensity; physiological characteristics.

Figure 1

Chl a content (A), Chl b content (B), Chl a + b content (C), and Chl a/b ratio (D) in leaves grown under different light intensities. Lowercase letters indicate significant differences under different light intensities (p < 0.05).

Figure 2

SOD activity (A), POD activity (B), CAT activity (C), and MDA contents (D) in leaves grown under different light intensities. Lowercase letters indicate significant differences under different light intensities (p < 0.05).

Figure 3

SS contents (A), SP contents (B), and Pro contents (C) in leaves grown under different light intensities. Lowercase letters indicate significant differences under different light intensities (p < 0.05).

Figure 4

Differentially expressed genes in root tissues of A. dahurica under different light intensities. (A) Bar graph of different differentially expressed genes. The left y-axis indicates upregulated genes, and the right y-axis indicates downregulated genes. (B) Venn diagram analysis of differentially expressed genes.

Figure 5

KEGG enrichment analysis of DEGs of root tissues A. dahurica under different light intensities. (A) CK vs. L1; (B) CK vs. L2; (C) CK vs. L3.

Figure 6

Expression patterns of genes involved in coumarin biosynthesis.

Figure 7

Heat map of differential expression of the genes in the coumarin biosynthesis pathway under different light intensities. (A) CK vs. L1; (B) CK vs. L2; (C) CK vs. L3. Red and green colors correspond to high and low expression levels, respectively.

Figure 8

The expression of nine randomly selected DEGs was determined by RNA-seq and qRT-PCR under different light intensities. The y-axis on the left indicates the qRT-PCR expression levels and the y-axis on the right indicates the RNA-seq data with Log2 (FPKM). The x-axis indicates the light treatments.