Abstract
Marigold (Tagetes erecta L.) is an important ornamental plant with a wide variety of flower colors. Despite its economic value, few biochemical and molecular studies have explored the generation of flower color in this species. To study the mechanism underlying marigold petal color, we performed a metabolite analysis and de novo cDNA sequencing on the inbred line ‘V-01’ and its petal color mutant ‘V-01M’ at four flower developmental stages. A total of 49,217 unigenes were identified from 24 cDNA libraries. Based on our metabolites and transcriptomic analyses, we present an overview of carotenoid biosynthesis, degradation, and accumulation in marigold flowers. The carotenoid content of the yellow mutant ‘V-01M’ was higher than that of the orange inbred line ‘V-01’, and the abundances of the yellow compounds lutein, neoxanthin, violaxanthin, zeaxanthin, and antheraxanthin were significantly higher in the mutant. During flower development, the carotenoid biosynthesis genes were upregulated in both ‘V-01’ and ‘V-01M’, with no significant differences between the two lines. By contrast, the carotenoid degradation genes were dramatically downregulated in the yellow mutant ‘V-01M’. We therefore speculate that the carotenoid degradation genes are the key factors regulating the carotenoid content of marigold flowers. Our research provides a large amount of transcriptomic data and insights into the marigold color metabolome.
Highlights
Abbreviations MEP 2-C-methyl-d-erythritol-4-phosphate pathway DEGs Differentially expressed genes deoxylulose-5-phosphate synthase (DXS) 1-Deoxylulose-5-phosphate synthase deoxylulose-5-phosphate reductionomerase (DXR) 1-Deoxylulose-5-phosphate reductionomerase GGPPS Geranylgeranyl pyrophosphate synthase phytoene synthase (PSY) Phytoene synthase phytoene desaturase (PDS) Phytoene desaturase Z-ISO 15-Cis-ζ-carotene isomerase ZDS ζ-Carotene desaturase (ZDS) carotenoid isomerase (CRTISO) Carotenoid isomerase LCY-B β-Cyclase HYD-B β-Hydroxylase LCY-E ε-Cyclase HYD-E ε-Hydroxylase CCD Carotenoid cleavage dioxygenase NCED 9-cis Epoxy carotenoid cleavage dioxygenase
We found that the orange variety ‘V-01’ and its natural mutant ‘V-01M’ had visible color differences starting from Stage III, resulting in completely different flower colors at Stage IV
No significant difference of carotenes were detected in ‘V-01’ and ‘V-01M’ (Fig. 1C). These results showed that the higher accumulation of yellow pigments in the ‘V-01M’ mutant likely resulted in its yellow petal color
Summary
Abbreviations MEP 2-C-methyl-d-erythritol-4-phosphate pathway DEGs Differentially expressed genes DXS 1-Deoxylulose-5-phosphate synthase DXR 1-Deoxylulose-5-phosphate reductionomerase GGPPS Geranylgeranyl pyrophosphate synthase PSY Phytoene synthase PDS Phytoene desaturase Z-ISO 15-Cis-ζ-carotene isomerase ZDS ζ-Carotene desaturase (ZDS) CRTISO Carotenoid isomerase LCY-B β-Cyclase HYD-B β-Hydroxylase LCY-E ε-Cyclase HYD-E ε-Hydroxylase CCD Carotenoid cleavage dioxygenase NCED 9-cis Epoxy carotenoid cleavage dioxygenase. The biosynthesis of the first carotenoid compound precursor, phytoene, requires four enzymes: 1-deoxylulose-5-phosphate synthase (DXS), 1-deoxylulose-5-phosphate reductionomerase (DXR), geranylgeranyl pyrophosphate synthase (GGPPS), and phytoene synthase (PSY). Another four enzymes participate in the catalytic reaction to transform colorless phytoene into red lycopene, namely phytoene desaturase (PDS), 15-cis-ζ-carotene isomerase (Z-ISO), ζ-carotene desaturase (ZDS), and carotenoid isomerase (CRTISO). CCD performs a major role in the degradation of a series of xanthophylls, such as lutein, zeaxanthin, violaxanthin, neoxanthin, and antheraxanthin, whereas NCED catalyzes the degradation of zeaxanthin
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