Space & Innovation

Now We Know Why Carrots Are Orange

A newly discovered gene in carrots gives rise to carotenoids, a critical source of Vitamin A and the pigment that turns some fruits and vegetables bright orange or red. →

Scientists unveiled Monday the gene in carrots that gives rise to carotenoids, a critical source of Vitamin A and the pigment that turns some fruits and vegetables bright orange or red.

Unpoetically dubbed DCAR_032551, the star gene emerged from the first complete decoding of the carrot genome, published in the scientific journal Nature Genetics.

"Vitamin A deficiency is a global health challenge," the study pointed out.

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"Its plentiful carotenoids make carrot an important source of provitamin A in the human diet."

Carotenoids were first discovered in carrots (hence the name), but which among the vegetable's newly tallied 32,115 genes was most responsible for their formation remained a mystery.

Daucus carota (the Latin name) now joins a select club of about a dozen veggies - including the potato, cucumber, tomato and pepper - whose complete genomes have been sequenced.

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Laying bare the humble carrot's genetic secrets will make it easier to enhance disease resistence and nutritive value in other species, the researchers said.

Having identified the mechanism controlling the accumulation of carotenoid, it may be possible - through gene-editing, for example - to import it to other staple root vegetables such as the cassava, native to South American and widely grown in Africa.

"These results will facilitate biological discovery and crop improvement in carrots and other crops," said Philipp Simon, senior author and a professor at the University of Wisconsin-Madison.

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Among vegetables spinach and peas are widely associated with growing up strong, but it's hard to beat the carrot when it comes to health boosters.

Carrots are loaded with beta-carotene, a natural chemical that the body can transform into Vitamin A.

The deeper the orange colour, the more beta-carotene.

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Vitamin A is essential for normal growth and development, the proper functioning of the immune system, and vision.

Carotenoids are also antioxidants, which are thought to protect against heart disease and some forms of cancer by neutralising so-called "free radicals", single oxygen atoms that can damage cells.

"Some of these compounds can prevent disease," Simon told AFP.

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Interestingly, carrots - along with many other plants - have about 20 percent more genes than humans.

Looking back at the plant's family tree, scientists have been able to determine that it split with the grape about 113 million years ago and from the kiwi about 10 million years after that, when dinosaurs still lorded over the planet.

Originally white, the wild ancestors of the carrot likely came from central Asia.

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Global crop production of the root has quadrupled in the last 40 years and is today eaten everywhere in the world.

There are currently no genetically modified carrots on the international market.

Seen here close-up under a dissecting microscope, the flowering plant

Amborella trichopoda

is the oldest known existing species of petal-bearing plants on Earth. Now in a series of reports published today in the journal Science, molecular geneticists have unlocked the genomic secrets of

Amborella

, and with it clues as to why flowers display such successful genetic diversity.

Many of

Amborella

's genes were distinct from those of non-flowering plants. In its mitochondrial DNA, which tends to change less than nuclear DNA,

Amborella

showed a shared affiliation with mosses and green algae. Biologist Danny W. Rice of Indiana University and his team hypothesize that wounded

Amborella

plants obtained the shared mitochondrial genomes as a result of horizontal gene transfer between these other organisms it was living in close proximity with millions of years ago. Here,

Amborella

genomic DNA is shown in blue, chloroplast DNA in green, and mitochondrial DNA in red.

Indeed, the team discovered that

Amborella

's mitochondrial genome provides the largest example of horizontal gene transfer – the acquisition of foreign genes from other species – in any organism. Shown here are male flowers of

Amborella

.

The Indiana University team -- working with biologists from the U.S. Department of Energy, Penn State University, and the Institute of Research for Development in New Caledonia -- showed for the first time that an organelle genome has captured an entire foreign genome, in this case, four of them: three green algae and one moss. It is also the first description of a land plant acquiring genes from green algae. Shown here are female flowers of

Amborella

.

"The

Amborella

mitochondrial genome is like the old lady in the song who swallows a fly, and then a spider, a bird, a cat, and so on, all the way to a horse, at which point, finally, "she's dead of course," said co-author of the study Jeff Palmer, a Distinguished Professor in the Indiana University Bloomington College of Arts and Sciences' Department of Biology. Shown here are

Amborella

female flowers and fruits.

"Likewise, the

Amborella

genome has swallowed whole mitochondrial genomes, of varying sizes, from a broad range of land plants and green algae. But instead of bursting from all this extra, mostly useless DNA, or purging the DNA, it's held on to it for tens of millions of years. So you can think of this genome as a constipated glutton, that is, a glutton that has swallowed whole genomes from other plants and algae and also retained them in remarkably intact form for eons," said Palmer in a press release. Shown here are

Amborella

in fruit.

View from the summit of Mt. Aoupine, New Caledonia. The flowering

Amborella

, whose mitochondrial genome is amazingly rich in foreign genes and even genomes, is endemic to the island of New Caledonia. The research on

Amborella

shows "compelling evidence that mitochondrial fusion is the driving force for mitochondrial gene transfer and that incompatibility in the mechanism of mitochondrial fusion between different phyla – plants versus animals or fungi – provides the major barrier to unconstrained mitochondrial 'sex' across the evolutionary tree of life," said Palmer.

The southwest-Australian Christmas tree,

Nuytsia floribunda

, which parasitizes the roots of grasses to obtain water and minerals. This parasite belongs to the group of parasitic plants (Santalales) from which the

Amborella

mitochondrial genome has captured many foreign genes by horizontal gene transfer.

A parasitic flowering plant (

Amyema scandens

) blooming in New Caledonia from its epicortical roots, which, like mistletoe, grow along the branch of its host tree. This parasite belongs to the same group of parasitic plants (Santalales) from which the

Amborella

mitochondrial genome has captured many foreign genes.

A parasitic flowering plant (

Hachettea austro-caledonica

) emerging from the ground to flower. This plant parasitizes the roots of other flowering plants and belongs to the group of parasitic plants (Santalales) from which the

Amborella

mitochondrial genome has captured many foreign genes. Picture taken in New Caledonia, the South Pacific island on which both

Amborella

and

Hachettea

are endemic.