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Carrot genome reveals the roots of its orange colour and high nutrition

ABC News logo ABC News 10/05/2016 Marc Llewellyn
Scientists have found a gene that turned white carrots into orange carrots. © Paul Asman and Jill Lenoble Scientists have found a gene that turned white carrots into orange carrots.

The humble supermarket carrot owes its deep orange colour to a newly-found gene, according to an analysis of the full carrot genome.

The findings could help boost beta-carotene in carrots, as well as the nutritional quality of a range of crops, including lettuce and celery.

The first full genome sequence of the carrot, published in Nature Genetics, sheds light on the vegetable's evolutionary origin, its distinctive orange colour, and its nutritious value.

While a few gaps remain, it represents one of the most comprehensive analyses of vegetable genetics so far.

The researchers identified more than 32,000 genes in a typical orange carrot, including around a third that were unique to the popular root vegetable.

They then sequenced the genomes of 35 different carrot specimens and subspecies, both wild and cultivated, in an attempt to understand how carrots evolved into those we find in our fridge.

Finally, they found a gene responsible for the high concentration of beta-carotene in the orange carrot taproot.

Beta-carotene, which is converted by the human body to vitamin A, belongs to a class of several hundred naturally occurring pigments called carotenoids.

It gives the yellow, orange or red colour to fruits and vegetables, as well as some animal products, like egg yolks and butter

"As well as sequencing the carrot genome we also studied specific genes, in particular part of the genome that includes the Y gene," Professor Philipp Simon from the University of Wisconsin-Madison said.

"We found that the Y-gene accounts for the accumulation of orange and yellow carotenoid pigments in carrot roots.

"It is one of two genes responsible for converting ancestral wild-type white carrots to orange ones," he said

From wild plant to the veggie patch

Flower of a wild carrot. © Phillip Simon Flower of a wild carrot.

Carrots are members of the Apiaceae family of plants, which include celery, parsley, fennel, coriander, dill and parsnip.

They are related to crops in the sunflower, artichoke and lettuce — the latter which it split from about 72 million years ago.

Historically, carrots had small white roots with a woody interior. They most likely came from areas of Iran and Afghanistan, where they still grow today.

Initially they were grown for their aromatic leaves, but over hundreds of years farmers turned a naturally occurring subspecies of the carrot into a larger, less woody root.

Domesticated yellow and purple carrots were found in Central Asia around 1,000 years ago, and an orange version emerged in late 16th century Holland, most probably from crossing yellow carrots with purple ones.

Carrots an important food crop

Vitamin A deficiency is a global health problem making the development of sustainable vitamin A sources is a priority for crop improvement, Professor Simon said.

"We expect the immediate users of the whole genome sequence will be public and private plant breeders who will use it for carrot disease resistance and seed production traits," he said.

As well as helping scientists develop carrots with improved nutritional value and other traits, the carrot genome sequence could provide insights into the genome sequence of other crops.

It could also be useful in genome editing technologies, when DNA is inserted, deleted or replaced in other organisms. This could increase beta-carotene levels in crops like cassava, a staple food in many developing countries, Professor Simon said.

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