Abstract
BackgroundCarrots (Daucus carota L.) are among the 10 most economically important vegetable crops grown worldwide. Purple carrot cultivars accumulate rich cyanidin-based anthocyanins in a light-independent manner in their taproots whereas other carrot color types do not. Anthocyanins are important secondary metabolites in plants, protecting them from damage caused by strong light, heavy metals, and pathogens. Furthermore, they are important nutrients for human health. Molecular mechanisms underlying anthocyanin accumulation in purple carrot cultivars and loss of anthocyanin production in non-purple carrot cultivars remain unknown.ResultsThe taproots of the three purple carrot cultivars were rich in anthocyanin, and levels increased during development. Conversely, the six non-purple carrot cultivars failed to accumulate anthocyanins in the underground part of taproots. Six novel structural genes, CA4H1, CA4H2, 4CL1, 4CL2, CHI1, and F3′H1, were isolated from purple carrots. The expression profiles of these genes, together with other structural genes known to be involved in anthocyanin biosynthesis, were analyzed in three purple and six non-purple carrot cultivars at the 60-day-old stage. PAL3/PAL4, CA4H1, and 4CL1 expression levels were higher in purple than in non-purple carrot cultivars. Expression of CHS1, CHI1, F3H1, F3′H1, DFR1, and LDOX1/LDOX2 was highly correlated with the presence of anthocyanin as these genes were highly expressed in purple carrot taproots but not or scarcely expressed in non-purple carrot taproots.ConclusionsThis study isolated six novel structural genes involved in anthocyanin biosynthesis in carrots. Among the 13 analyzed structural genes, PAL3/PAL4, CA4H1, 4CL1, CHS1, CHI1, F3H1, F3′H1, DFR1, and LDOX1/LDOX2 may participate in anthocyanin biosynthesis in the taproots of purple carrot cultivars. CHS1, CHI1, F3H1, F3′H1, DFR1, and LDOX1/LDOX2 may lead to loss of light-independent anthocyanin production in orange and yellow carrots. These results suggest that numerous structural genes are involved in anthocyanin production in the taproots of purple carrot cultivars and in the loss of anthocyanin production in non-purple carrots. Unexpressed or scarcely expressed genes in the taproots of non-purple carrot cultivars may be caused by the inactivation of regulator genes. Our results provide new insights into anthocyanin biosynthesis at the molecular level in carrots and for other root vegetables.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0262-y) contains supplementary material, which is available to authorized users.
Highlights
Carrots (Daucus carota L.) are among the 10 most economically important vegetable crops grown worldwide
We described the presence of the UDP-galactose: cyanidin 3-O-galactosyltransferase (UCGT) in the purple carrot cultivars in our previous study [25]
In the six other carrot cultivars, no purple or dark coloring was detected in these taproot parts, with the exception of the hypocotyl-derived root part of 90- and 120-day-old ‘Kuroda’, 90-day-old ‘Sanhongliucun’, and 120-day-old ‘Junchuanhong’; these displayed dark color in the epidermis when exposed to light (Figure 2)
Summary
Carrots (Daucus carota L.) are among the 10 most economically important vegetable crops grown worldwide. Purple carrot cultivars accumulate rich cyanidin-based anthocyanins in a light-independent manner in their taproots whereas other carrot color types do not. Anthocyanins are important secondary metabolites in plants, protecting them from damage caused by strong light, heavy metals, and pathogens. They are important nutrients for human health. Anthocyanins protect plants from strong light, heavy metals, and pathogens, and play an important role in flowers [3,4]. As they have low toxicity and vary in color they are often used as healthier alternatives to synthetic colorants [5]. Previous studies have confirmed that anthocyanins provide antioxidants for human health that protect against a broad range of diseases, including a high blood cholesterol level, cardiovascular disease, and ultraviolet radiation damage [2,6,7,8]
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