A cluster of MYB transcription factors regulates anthocyanin biosynthesis in carrot (Daucus carota L.) root and petiole

Authors: IORIZZO, MASSIMO - North Carolina State University; CAVAGNARO, PABLO - University Of Cuyo; BOSTAN, HAMED - North Carolina State University; ZHAO, YUNYANG - North Carolina State University; ZHANG, JIANHUI - North Carolina State University; Simon, Philipp

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 1/14/2019
Citation: Iorizzo, M., Cavagnaro, P.F., Bostan, H., Zhao, Y., Zhang, J., Simon, P.W. 2019. A cluster of MYB transcription factors regulates anthocyanin biosynthesis in carrot (Daucus carota L.) root and petiole. Frontiers in Plant Science. 9:1927. https://doi.org/10.3389/fpls.2018.01927.
DOI: https://doi.org/10.3389/fpls.2018.01927

Interpretive Summary: The first colors of carrot, early in its domestication 1000 years ago, were yellow and purple. Purple carrots are also being grown today. Their purple color is due to anthocyanin pigments, and some understanding of the genetic control of anthocyanin color of carrots is known, but the genes underlying that control are not known. This study investigated the identity of one of those genes. Based upon genetic mapping and gene expression analysis, the underlying genetic element was discovered. This information is of interest to plant biologists and nutritionists researching anthocyanins, as well as seed companies developing new purple carrot cultivars.

Technical Abstract: Purple carrots can accumulate large quantities of anthocyanins in their root 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 petioles. 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 kb 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 structural anthocyanin genes were present in this region. Comparative transcriptome analysis in anthocyanin-pigmented and non-pigmented root and petiole tissues 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. DcMYB7 and DcMYB11 are candidate genes for root and petiole anthocyanin pigmentation of all the purple carrot sources in this study. Since DcMYB7 is co-expressed with DcMYB11 in purple petioles, this gene may act also as a co-regulator of anthocyanin pigmentation in the petioles. 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 plays a major role in the regulation of anthocyanin biosynthesis in carrot root and petioles, while DcMYB11 modulates pigmentation only in petioles.