Most nutritionists advise people to “eat the rainbow” to balance their diet—think greens like kale, purples like eggplant, reds like tomatoes. Consuming nutritious and naturally occuring orange foods like carrots packed with vitamin A, fiber, antioxidants, and pigments called carotenoids is a must to get a full and healthy spectrum. Carotenoids even got their name because they were first isolated from carrots. But what is exactly behind the bright hue of some of our favorite carrots? Only three specific genes are required to give orange carrots their signature color, according to a study published September 28 in the journal Nature Plants.
In the study, a team from North Carolina State University and the University of Wisconsin-Madison looked at the genetic blueprints of more than 600 varieties of carrots. Surprisingly, they found that these three required genes all need to be recessive, or turned off.
“Normally, to make some function, you need genes to be turned on,” study co-author and North Carolina State University horticultural scientist Massimo Iorizzo said in a statement. “In the case of the orange carrot, the genes that regulate orange carotenoids—the precursor of vitamin A that have been shown to provide health benefits—need to be turned off,” Iorizzo said.
In 2016, this team sequenced the carrot genome for the first time and also uncovered the gene involved in the pigmentation of yellow carrot. For this new study, they sequenced 630 carrot genomes as part of a continuing study on the history and domestication of the crunchy root veggie.
The team performed selective sweeps, or structural analyses among five different carrot groups. During these sweeps, they looked for areas of the genome that are heavily selected in certain groups. They found that many of the genes involved in flowering were under selection, primarily to delay the flowering process. This event causes the edible root that we eat called the taproot to turn woody and inedible.
“We found many genes involved in flowering regulation that were selected in multiple populations in orange carrot[s], likely to adapt to different geographic regions,” said Iorizzo.
Additionally, the study created a general timeline of carrot domestication and found more evidence that carrots were domesticated in the 9th or 10th century CE in western and central Asia.
“Purple carrots were common in central Asia along with yellow carrots. Both were brought to Europe, but yellow carrots were more popular, likely due to their taste,” said Iorizzo.
In about the 15th or 16th century, orange carrots made their appearance in western Europe, potentially as the result of crossing a yellow carrot with a white one. The bright color and sweet flavor of orange carrots likely made it more popular than other varieties, so farmers continued selecting for them. In northern Europe, different types of orange carrots were developed in the 16th and 17th centuries and orange carrots of various shades can be seen in paintings from that area. They continued to grow in popularity as more understanding about the importance of alpha- and beta-carotenes and vitamin A in the diet for eye health progressed in the late 19th and early 20th centuries.
The findings in this study shed more light on the traits that are important to improving carrots and could lead to better health benefits from the nutritious vegetable.