Abstract
BackgroundAnthocyanins have distinct biological functions in plant coloring, plant defense against strong light, UV irradiation, and pathogen infection. Aromatic hydroxyl groups and ortho-dihydroxyl groups in anthocyanins are able to inhibit free-radical chain reactions and hydroxyl radicals. Thus, anthocyanins play an antioxidative role by removing various types of ROS. Pepper is one of the solanaceous vegetables with the largest cultivation area in China. The purple-fruited pepper is rich in anthocyanins, which not only increases the ornamental nature of the pepper fruit but also benefits the human body. In this experiment, light-induced regulatory pathways and related specific regulators of anthocyanin biosynthesis were examined through integrative transcriptomic and metabolomic analysis.ResultsResults revealed that delphinium 3-O-glucoside significantly accumulated in light exposed surface of pepper fruit after 48 h as compared to shaded surface. Furthermore, through strand-specific sequencing technology, 1341 differentially expressed genes, 172 differentially expressed lncRNAs, 8 differentially expressed circRNAs, and 28 differentially expressed miRNAs were identified significantly different among both surfaces. The flavonoid synthesis pathway was significantly enriched by KEGG analysis including SHT (XM_016684802.1), AT-like (XM_016704776.1), CCoAOMT (XM_016698340.1, XM_016698341.1), CHI (XM_016697794.1, XM_016697793.1), CHS2 (XM_016718139.1), CHS1B (XM_016710598.1), CYP98A2-like (XM_016688489.1), DFR (XM_016705224.1), F3’5’H (XM_016693437.1), F3H (XM_016705025.1), F3’M (XM_016707872.1), LDOX (XM_016712446.1), TCM (XM_016722116.1) and TCM-like (XM_016722117.1). Most of these significantly enriched flavonoid synthesis pathway genes may be also regulated by lncRNA. Some differentially expressed genes encoding transcription factors were also identified including MYB4-like (XM_016725242.1), MYB113-like (XM_016689220.1), MYB308-like (XM_016696983.1, XM_016702244.1), and EGL1 (XM_016711673.1). Three ‘lncRNA-miRNA-mRNA’ regulatory networks with sly-miR5303, stu-miR5303g, stu-miR7997a, and stu-miR7997c were constructed, including 28 differentially expressed mRNAs and 6 differentially expressed lncRNAs.ConclusionPossible light regulated anthocyanin biosynthesis and transport genes were identified by transcriptome analysis, and confirmed by qRT-PCR. These results provide important data for further understanding of the anthocyanin metabolism in response to light in pepper.
Highlights
Anthocyanins have distinct biological functions in plant coloring, plant defense against strong light, UV irradiation, and pathogen infection
It undergoes a series of enzyme activities, such as cinnamic acid 4-hydroxylase (C4H), 4-coumarin-CoA ligase (4Cl), ketone synthase (CHS), chalcone isomerase (CHI), and flavone 3-hydroxylase (F3H) that catalyzes the synthesis of dihydrokaempferol
Among the 19 basic helix-loop-helix (bHLH) transcription factors that we identified with significant differences, most importantly EGL1 (XM_016711673.1) expression correlated with degree of anthocyanin synthesis which indicates its important role in the light regulated flavonoid biosynthesis pathway
Summary
Anthocyanins have distinct biological functions in plant coloring, plant defense against strong light, UV irradiation, and pathogen infection. The purple-fruited pepper is rich in anthocyanins, which increases the ornamental nature of the pepper fruit and benefits the human body. In this experiment, light-induced regulatory pathways and related specific regulators of anthocyanin biosynthesis were examined through integrative transcriptomic and metabolomic analysis. Taking a synthetic pathway of capsicum flavonoids as an example, phenylalanine is first catalyzed by phenylalanine ammonia-lyase to cinnamic acid It undergoes a series of enzyme activities, such as cinnamic acid 4-hydroxylase (C4H), 4-coumarin-CoA ligase (4Cl), ketone synthase (CHS), chalcone isomerase (CHI), and flavone 3-hydroxylase (F3H) that catalyzes the synthesis of dihydrokaempferol. Under the catalysis of anthocyanin synthase (ANS), colored anthocyanins are synthesized and transported by transferase to the vacuole for storage
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