A study of the genome provides insights into pigmentation and domestication, with three recessive genes responsible for carrots' orange color, which sheds light on carrot breeding and health benefits. The study traces carrots from their origins in Asia in the 9th century to the popularity of orange carrots in Europe in the 15th century, highlighting their alluring color and flavor.
A recent study analyzed the genetic sequences of more than 600 carrot varieties and found that three specific genes are responsible for the orange color of carrots. Interestingly, for carrots to appear this orange, these genes must be recessive, essentially turned off. This finding provides valuable insight into key characteristics that improve carrot quality, potentially improving the health benefits of this vegetable.
"Typically, for certain functions to work, genes have to be turned on," said Massimo Iorizzo, associate professor of horticultural sciences at North Carolina State University's Institute for Plants for Human Health. "In the case of orange carrots, the gene that regulates orange carotenoids, precursors to vitamin A that have been shown to have health benefits, needs to be turned off."
Carrots, especially orange carrots, contain high amounts of carotenoids, which help reduce the risk of eye diseases and other diseases. Orange carrots are the richest plant source of vitamin A in the American diet.
Researchers at North Carolina State University, working with colleagues at the University of Wisconsin-Madison, sequenced 630 carrot genomes to continue studying the history and domestication of orange carrots; a 2016 study published in Nature Genetics by these researchers provided the first carrot genome sequence and discovered genes involved in the formation of yellow carrot pigments.
The researchers performed what's called a selectivity scan - a structural analysis - in five different carrot groups to find regions of the genome that are heavily selected in certain groups. They found that many genes involved in flowering were under selection - primarily to delay the flowering process. Flowering causes the taproot (the root we eat) to become lignified and rendered inedible.
"We found a number of genes involved in flowering regulation that were selected in multiple populations of orange carrots, most likely to adapt to different geographic regions," Iorizzo said.
The study also provides further evidence that carrots were domesticated in western and central Asia in the 9th or 10th century. Purple and yellow carrots are common in Central Asia. Both types of carrots were brought to Europe, but yellow carrots were more popular, most likely due to their flavor.
Orange carrots appeared in Western Europe around the 15th or 16th century, probably as a result of hybridization between white and yellow radish.
"This study essentially reconstructs the chronology of when carrots were domesticated and then selected for orange carrots," he said. "Orange carrots may be the result of a cross between white and yellow radish, because white and yellow radish are at the base of the orange carrot phylogenetic tree."
Orange carrots' color and sweeter taste made them popular, and farmers selected for these traits. Different types of orange carrots were developed in Northern Europe during the 16th and 17th centuries, which coincide with the different shades of orange carrots that appear in paintings of the era. Later, as people in the late 19th and early 20th centuries gained a better understanding of alpha-carotene and beta-carotene, the precursors of vitamin A in the diet, orange carrots grew in popularity.