The U.S. research project is now studying the genetic mechanism that controls traits important for carrot production
Many vegetables are so familiar, they are taken for granted, especially something as commonplace as carrots.
But recently, researchers at North Carolina State University delved into the familiar carrot in a study exploring what gives the vegetable its orange colour.
Researchers looked at the genetic blueprints of more than 600 types of carrots and found that three specific genes give carrots their distinctive orange colour. These three genes all need to be recessive, or turned off, to function.
Massimo Iorizzo, associate professor of horticultural science in the university’s Plants for Human Health Institute, said researchers looked at the structural analyses among five different carrot groups to find areas of the genome that were heavily selected. They found many genes involved in flowering were under selection, mostly to delay the flowering process. It is the flowering process that causes the edible root to turn woody and unappetizing.
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The study not only looked at the genetic influence of the orange carrot but reconstructed the chronology of carrot domestication, which occurred in the ninth or 10th centuries in western and central Asia where purple, white and yellow carrots were common. They were brought to Europe, where yellow carrots were more popular, probably due to flavour.
The orange carrot first appeared in the Netherlands in the 16th century, likely because of farmers crossing white and yellow carrots.
“The appearance of the orange phenotype likely occurred naturally and was then selected by farmers or early breeders for improved production or desired culinary reasons,” said Iorizzo. “Once selected, these plants were used for pollination with other carrot types and selected based on their phenotypes.”
Orange carrots grew extensively in popularity, especially with the discovery and understanding of the value of carotenes and dietary vitamin A in the late 19th and early 20th centuries.
“Orange carrots contain high alpha and beta carotene, which are the precursor of vitamin A, an essential micronutrient in our diet,” he said.
“Vitamin A plays an important role in our bodies, including maintaining a healthy immune system, for normal growth and development, and for reproduction. Purple, red and yellow carrots contain lycopene, lutein and anthocyanin, respectively. These compounds are not essential nutrients, but several studies have associated the consumption of these compounds with multiple health benefits including antidiabetic, anticancer, anti-inflammatory, antimicrobial and anti-obesity effects as well as prevention of cardiovascular diseases.”
In addition to crossbreeding, the orange-coloured carrot could have emerged naturally because of geographical or regional adaptations or localized climates.
“It is possible that the natural selection of each of the three individual recessive alleles at the Or-like, RECl and Exl was driven by environmental adaptation to new geographic regions where (the) carrot was growing,” he said.
Why these three genes all are recessive is still unknown.
“We do not know why natural selection (by the plants) selected the recessive alleles but if the plants harbouring these mutations survived, it implies that they provided some advantages for them. Follow-up selection by farmers and breeders played a major role in fixing these recessive mutations.”
In response to the study, he said farmers have been curious about the research, the discovery of the genes and the historical context.
“Breeders were excited for the several discoveries reported in the study as well as for the large amount of resource releases (several new genomes),” he said. “This information helps them to advance the selection of new and improved carrot cultivars.”
Research is continuing and the current focus is to study the genetic mechanism controlling traits that are important for carrot production.
According to the report, carrot production has increased steadily over the past 50 years, primarily because of their adaptability, nutritional value and the diversification of the vegetable for both the fresh and processed markets. Those attributes are expected to continue to drive markets.
The research was recently published in the journal Nature Plants.
