Science - January 20, 2010

Conquering Asia with the pink tomato

Plant Research International has discovered the gene that makes tomatoes pink. Plant breeding companies are showing a great deal of interest in this gene; they are hoping to use it to conquer the Chinese and Japanese markets.

Tomatoes generally turn red but a mutation in the tomato genome makes them turn pink instead. This mutation was described in the literature as early as 1925 but it was still not known what caused it. In this month's Plant Physiology a research team led by Arnaud Bovy explains that the pink colour is due to a mutation in a single gene. This mutation blocks the production of a key group of compounds, the flavonoids. They are found in the tomato skin and are yellow in colour. They combine with another pigment, red lycopene, to create the typical red colour of ripe tomatoes. If the yellow flavonoid is missing, the tomato becomes pink.
Pink tomatoes are unknown in the Netherlands but are very popular in countries like China and Japan. They have been grown there for years without the plant breeders knowing the exact genetic cause. European plant breeding companies would like to have pink versions of their tomato varieties to sell in the Asian market. They will now be able to breed such pink versions more successfully and efficiently.
Bovy's group carries out a great deal of research into flavonoids, not so much because of their role in determining the colour of various plants but because they are considered healthy food components of fruit and vegetables. Flavonoids probably function as antioxidants, reducing the likelihood of cardiovascular illnesses.
Regulating gene
His group carried out biochemical studies of pink tomatoes and discovered that one important flavonoid was missing. Further research showed that a whole series of genes involved in the production of this compound were no longer expressed. It finally turned out that a single regulating gene was responsible for switching these genes on and off. 'When we tested our findings on different tomato varieties, the relationship between this gene and the pink colour turned out to be one hundred per cent', says Bovy. Plant breeders can now combine the pink colour with other positive characteristics in their product range, such as disease resistance and taste.
Eighteen months ago Bovy was involved from the sidelines in the development of a purple tomato that produces extra flavonoids, giving it a promising effect on health as demonstrated in animal experiments. English colleagues have taken the lead in developing this tomato further.