An international team lead by Sanwen Huang, professor of Institute of Vegetables and Flowers (IVF) and Deputy Director of Shenzhen Agricultural Genomic Institute (AGI), CAAS, revealed the molecular basis of biosynthesis, regulation and domestication of bitterness in cucumber. They provided a good example on integration of big data, such as genomics, variation map, transcriptome, with metabolomics and molecular tools to solve a breeding problem in non-model plant. These findings are published in the journal Science in December, 2014.

Widely consumed as vegetables and fruits, cucumber, pumpkin and their relatives were domesticated from their wild ancestors that had extremely bitter fruits. Due to the inadequate domestication, non-bitter cultivars would turn bitter when grown under drought or temperature stress, which can seriously affect fruit quality and marketability.

"You don't eat wild cucumber, unless you want to use it as a purgative," said William Lucas, professor of plant biology at the University of California, Davis and coauthor of the paper. Fortunately, a mutation occurred at the promoter region of the fruit bitterness gene (Bt) that resulted in the full domestication was identified. “This SNP will be applied in the non-bitter cucumber breeding to totally avoid this unpleasant trait”, said Sanwen Huang, who has organized or participated multiple international consortia for genome sequencing and developed genomics as new tools to improve molecular assisted breeding and basic research in China.

In the plant family Cucurbitaceae, bitterness is caused by a group of highly oxygenated tetracyclic triterpenes, the cucurbitacins. Nine genes (1 OSC, 7 P450s and 1 ACT) participate in the biosynthetic pathway, four of which have been functionally elucidated. These biosynthetic genes are directly regulated by two master regulators, Bl (bitter leaf) and Bt, in leaf and fruit respectively.