Dataset Information

A MYB transcription factor, DcMYB6, is involved in regulating anthocyanin biosynthesis in purple carrot taproots.

ABSTRACT: Carrots are widely grown and enjoyed around the world. Purple carrots accumulate rich anthocyanins in the taproots, while orange, yellow, and red carrots accumulate rich carotenoids in the taproots. Our previous studies indicated that variation in the activity of regulatory genes may be responsible for variations in anthocyanin production among various carrot cultivars. In this study, an R2R3-type MYB gene, designated as DcMYB6, was isolated from a purple carrot cultivar. In a phylogenetic analysis, DcMYB6 was grouped into an anthocyanin biosynthesis-related MYB clade. Sequence analyses revealed that DcMYB6 contained the conserved bHLH-interaction motif and two atypical motifs of anthocyanin regulators. The expression pattern of DcMYB6 was correlated with anthocyanin production. DcMYB6 transcripts were detected at high levels in three purple carrot cultivars but at much lower levels in six non-purple carrot cultivars. Overexpression of DcMYB6 in Arabidopsis led to enhanced anthocyanin accumulation in both vegetative and reproductive tissues and upregulated transcript levels of all seven tested anthocyanin-related structural genes. Together, these results show that DcMYB6 is involved in regulating anthocyanin biosynthesis in purple carrots. Our results provide new insights into the regulation of anthocyanin synthesis in purple carrot cultivars.

SUBMITTER: Xu ZS

PROVIDER: S-EPMC5366895 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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A MYB transcription factor, DcMYB6, is involved in regulating anthocyanin biosynthesis in purple carrot taproots.

Xu Zhi-Sheng ZS Feng Kai K Que Feng F Wang Feng F Xiong Ai-Sheng AS

Scientific reports 20170327

Carrots are widely grown and enjoyed around the world. Purple carrots accumulate rich anthocyanins in the taproots, while orange, yellow, and red carrots accumulate rich carotenoids in the taproots. Our previous studies indicated that variation in the activity of regulatory genes may be responsible for variations in anthocyanin production among various carrot cultivars. In this study, an R2R3-type MYB gene, designated as DcMYB6, was isolated from a purple carrot cultivar. In a phylogenetic analy ...[more]

PMID: 28345675

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Project description:BACKGROUND: Red coloration of fruit is an important trait in apple, and it is mainly attributed to the accumulation of anthocyanins, a class of plant flavonoid metabolites. Anthocyanin biosynthesis is genetically determined by structural and regulatory genes. Plant tissue pigmentation patterns are mainly controlled by expression profiles of regulatory genes. Among these regulatory genes are MYB transcription factors (TFs), wherein the class of two-repeats (R2R3) is deemed the largest, and these are associated with the anthocyanin biosynthesis pathway. Although three MdMYB genes, almost identical in nucleotide sequences, have been identified in apple, it is likely that there are other R2R3 MYB TFs that are present in the apple genome that are also involved in the regulation of coloration of red color pigmentation of the skin of apple fruits. RESULTS: In this study, a novel R2R3 MYB gene has been isolated and characterized in apple. This MYB gene is closely related to the Arabidopsis thaliana AtMYB3, and has been designated as MdMYB3. This TF belongs to the subgroup 4 R2R3 family of plant MYB transcription factors. This apple MdMYB3 gene is mapped onto linkage group 15 of the integrated apple genetic map. Transcripts of MdMYB3 are detected in all analyzed tissues including leaves, flowers, and fruits. However, transcripts of MdMYB3 are higher in excocarp of red-skinned apple cultivars than that in yellowish-green skinned apple cultivars. When this gene is ectopically expressed in Nicotiana tabacum cv. Petite Havana SR1, flowers of transgenic tobacco lines carrying MdMYB3 have exhibited increased pigmentation and accumulate higher levels of anthocyanins and flavonols than wild-type flowers. Overexpression of MdMYB3 has resulted in transcriptional activation of several flavonoid pathway genes, including CHS, CHI, UFGT, and FLS. Moreover, peduncles of flowers and styles of pistils of transgenic plants overexpressing MdMYB3 are longer than those of wild-type plants, thus suggesting that this TF is involved in regulation of flower development. CONCLUSIONS: This study has identified a novel MYB transcription factor in the apple genome. This TF, designated as MdMYB3, is involved in transcriptional activation of several flavonoid pathway genes. Moreover, this TF not only regulates the accumulation of anthocyanin in the skin of apple fruits, but it is also involved in the regulation of flower development, particularly that of pistil development.

Project description:Purple carrots can accumulate large quantities of anthocyanins in their roots and -in some genetic backgrounds- petioles, and therefore they represent an excellent dietary source of antioxidant phytonutrients. In a previous study, using linkage analysis in a carrot F2 mapping population segregating for root and petiole anthocyanin pigmentation, we identified a region in chromosome 3 with co-localized QTL for all anthocyanin pigments of the carrot root, whereas petiole pigmentation segregated as a single dominant gene and mapped to one of these "root pigmentation" regions conditioning anthocyanin biosynthesis. In the present study, we performed fine mapping combined with gene expression analyses (RNA-Seq and RT-qPCR) to identify candidate genes controlling anthocyanin pigmentation in the carrot root and petiole. Fine mapping was performed in four carrot populations with different genetic backgrounds and patterns of pigmentation. The regions controlling root and petiole pigmentation in chromosome 3 were delimited to 541 and 535 kb, respectively. Genome wide prediction of transcription factor families known to regulate the anthocyanin biosynthetic pathway coupled with orthologous and phylogenetic analyses enabled the identification of a cluster of six MYB transcription factors, denominated DcMYB6 to DcMYB11, associated with the regulation of anthocyanin biosynthesis. No anthocyanin biosynthetic genes were present in this region. Comparative transcriptome analysis indicated that upregulation of DcMYB7 was always associated with anthocyanin pigmentation in both root and petiole tissues, whereas DcMYB11 was only upregulated with pigmentation in petioles. In the petiole, the level of expression of DcMYB11 was higher than DcMYB7. DcMYB6, a gene previously suggested as a key regulator of carrot anthocyanin biosynthesis, was not consistently associated with pigmentation in either tissue. These results strongly suggest that DcMYB7 is a candidate gene for root anthocyanin pigmentation in all the genetic backgrounds included in this study. DcMYB11 is a candidate gene for petiole pigmentation in all the purple carrot sources in this study. Since DcMYB7 is co-expressed with DcMYB11 in purple petioles, the latter gene may act also as a co-regulator of anthocyanin pigmentation in the petioles. This study provides linkage-mapping and functional evidence for the candidacy of these genes for the regulation of carrot anthocyanin biosynthesis.

Project description: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.

Dataset Information

A MYB transcription factor, DcMYB6, is involved in regulating anthocyanin biosynthesis in purple carrot taproots.

Publications

A MYB transcription factor, DcMYB6, is involved in regulating anthocyanin biosynthesis in purple carrot taproots.

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