Researchers identify genes for bitterness in cucumbers

An international team led by Chinese researchers said Thursday they have identified the genes responsible for the intense bitter taste of some cucumbers, a plague to lovers of this vegetable.

The research, published in the U.S. journal Science, revealed how cucumbers, believed native to India, were domesticated from their wild ancestors that have extremely bitter fruits to make them more edible.

"Wide cucumbers have been used as a purgative in India and because their fruits are as bitter as wormwood they are not sold on the market," Huang Sanwen of the Chinese Academy of Agricultural Sciences, who led the study, told Xinhua. "No one wants to eat wide cucumbers."

Today's domestic cucumbers are delicious, stress conditions such as a lack of water or temperatures too cold or too hot, however, are still able to cause them to bear bitter tasting fruits, Huang said.

In the new study, Huang and colleagues performed genomic and biochemical analyses on 115 diverse cucumber lines to unravel the biosynthetic pathway involved in domesticating cucumbers to the non-bitter fruits people eat today.

They were able to identify nine genes involved in making cucurbitacins, which confer a bitter taste in cucumbers, and showed that the trait can be traced to another two genes that switch on these nine genes to produce the compounds.

In short, bitterness is controlled by two "master switch" genes, "Bl" which confers bitterness in leaves and "Bt", which leads to bitter fruit, Huang said.

The study also found that a mutation in the Bt gene is able to keep domestic cucumbers from becoming bitter even when exposed to stress conditions such as cold temperatures.

Cucurbitacins protect wild plants against predators and have also been showed to have the ability to kill or suppress growth of cancer cells.

"The new knowledge on cucurbitacin biosynthesis laid a solid foundation for biological manufacturing and engineering of the compounds as antitumor drugs," Huang said.

The study also involved researchers from Nanjing Agricultural University, Hunan Agricultural University, Hunan Academy of Agricultural Sciences and Chinese Academy of Sciences, as well as researchers from universities of the United States, Japan and the Netherlands.