The influence of the Or and Carotene Hydroxylase genes on carotenoid accumulation in orange carrots [Daucus carota (L.)]

Authors: COE, KEVIN - University Of Wisconsin; ELLISON, SHELBY - University Of Wisconsin; Senalik, Douglas; DAWSON, JULIE - University Of Wisconsin; Simon, Philipp

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2021
Publication Date: 7/21/2021
Citation: Coe, K., Ellison, S., Senalik, D.A., Dawson, J., Simon, P.W. 2021. The influence of the Or and Carotene Hydroxylase genes on carotenoid accumulation in orange carrots [Daucus carota (L.)]. Theoretical and Applied Genetics. 134:3351–3362. https://doi.org/10.1007/s00122-021-03901-3.
DOI: https://doi.org/10.1007/s00122-021-03901-3

Interpretive Summary: Before 1400, only yellow and purple carrots were recorded in historical records, but in the early 1400’s orange carrots were first reported in southern Europe, and today most carrots grown worldwide are orange. Carrots are orange because they accumulate of alpha- and beta-carotene, which are converted to vitamin A when we eat orange carrots. Until recently, two genes had been identified that account for the dramatic shift from yellow to orange carrots. But within the last decade two more genes, Or and CH, were found to also account for the orange color typical of carrots. In this study we evaluated the magnitude of the effects that the Or and CH genes have on carrot color. Using a carrot population that varied for the incidence of the Or and CH genes, we determined that both of these genes have a significant effect in carotene content, and the CH gene also affects the relative amount of alpha-carotene in carrots. This study is of interest to carrot breeders and growers, and because of the impact of carrot carotenes on human health, it is also of interest to nutritionists.

Technical Abstract: Carrot taproot color results from the accumulation of various carotenoid and anthocyanin pigments. Recently, the Or gene was identified as a candidate gene associated with the accumulation of beta-carotene and other provitamin A carotenoids in roots. The specific molecular mechanisms involved with this process, as well as the interactions between Or and the other genes involved in this process are not well understood. In order to better characterize the effect that Or alleles have on conditioning the accumulation of carotenoids in roots, we analyzed an F3 family fixed homozygous recessive for y and y2, derived from a cross between an orange carrot and a white wild carrot, segregating for the two known Or alleles, which we name Orc and Orw. QTL mapping across three different environments revealed that the accumulation of several carotenoids was associated with the Orc allele, with consistent patterns across environments. A second QTL on chromosome 7, harboring a carotene hydroxylase gene homologous to Lut5 in Arabidopsis, was also associated with the accumulation of several carotenoids. Two alleles for this gene, which we name CHc and CHw, were discovered to be segregating in this population. Our study provides further evidence that Or and CH are likely involved with controlling the accumulation of beta-carotene and may be involved with modulating carotenoid flux in carrot, demonstrating that both were important domestication genes in carrot.