Tomatoes capable of producing a commonly used orange colour in foods may arise after scientists in France tackle the bixin conundrum.
The pigment bixin, used in foods and cosmetics, is harvested from the single, heavily fruiting, small tropical tree, Bixa orellana.
Researchers from CNRS and Université Louis Pasteur in Strasbourg, France figured out exactly how the plant itself produces bixin.
But crucially, in addition to locating the three crucial genes, they demonstrated that lycopene - the compound known to make tomatoes red and a powerful antioxidant - is the physical precursor to bixin.
The authors moved to replicate this biosynthetic pathway in another organism and selected E. coli because "you can insert all the genes at once. Tomatoes will be more complicated," explained senior author Bilal Camara.
Bixin genes are not the only genetic ingredient. The scientists added these genes to E. coli already engineered to produce lycopene. When the E. coli growing in test tubes began to produce bixin, they did not change colour because the lycopene had already turned these single-celled bacteria red.
The next step, according to Camara, is to insert the genes that produce this pigment into tomatoes, or other fruit that produce large amounts of lycopene naturally.
"Tomatoes could become bixin factories," said Camara who explained that the three bixin genes would each have to be added to separate plants. These plants could be crossed to breed plants with the full complement of bixin genes. Alternatively, a vector allowing insertion of several genes could be used. Camara is hoping to have bixin-producing tomatoes in about two years.
"Living organisms can be engineered to constantly make the enzymes required for bixin synthesis. It's the best way," said Camara who explained that managing all the enzymes in a non-biological synthesis scenario would be difficult.
"The bixin produced in E. coli is exactly the same compound as the bixin harvested from the plant. There is no difference," said Camara.
The yellow-orange pigment is used in a wide range of products because it easily mixes and dissolves into both water-based and oil-based products destined for human consumption and human adornment.
Full findings are reported in the 27 June issue of the journal Science, published by the American Association for the Advancement of Science.