The genome sequence of watermelon has been published by an international consortium of scientists including researchers at UC Davis. The information could dramatically accelerate both breeding of more nutritious, tasty and disease-resistant fruit, and progress on understanding the role of the plant vascular system as an information superhighway. The watermelon genome sequence was published Nov. 25 in the online version of the journal Nature Genetics.

The genome of the domesticated watermelon contains 23,440 genes, roughly the same number of genes as in humans. The team compared the genomes of 20 different watermelons and developed a first-generation genetic variation map for watermelon. This information allowed them to identify genomic regions that have been under human selection, including those associated with fruit color, taste and size.

Professor William Lucas, chair of the Department of Plant Biology and one of the leaders of the genome project, and colleagues at UC Davis are using the previously published cucumber genome and the newly decoded watermelon genome to explore fundamental questions about the plant vascular system, which carries water and nutrients through the plant. They hope to discover the role played by proteins and RNA species that traffic through the vascular system, many of which are likely to be involved in regulating important agricultural traits.

"Watermelons are a model system for studying the evolution of long-distance signaling processes that occur through the plant vascular system. Knowledge relating to these regulatory mechanisms can be harnessed by breeders to develop watermelons having enhanced properties, including increased water use efficiency, enhanced nutritional value and engineered resistance to pathogens," Lucas said.

The researchers also discovered that a large portion of disease resistance genes were lost in the domestication of watermelon. Breeders ultimately may be able to use the genome information to recover some of these natural disease defenses.

Believed to have originated in Africa, watermelons were cultivated by Egyptians more than 4,000 years ago, and the fruit was a source of water in dry, desert conditions. They are now consumed throughout the world, with more than 200 varieties in global commercial production. China leads in global production of the fruit, and the United States ranks fourth with more than 40 states involved in the industry.

Despite being more than 90 percent water, watermelons contain important nutrients like vitamins A and C and lycopene, a compound that gives some fruits and vegetables their red and orange color. The fruit also contains citrulline, a novel amino acid that has been reported to have beneficial effects in terms of maintaining a healthy heart.

Institutions collaborating on the project in addition to UC Davis were: Beijing Academy of Agriculture and Forestry Sciences, China; Boyce Thompson Institute for Plant Research, Cornell University; BGI-Shenzhen, China; Fudan University, Shanghai, China; Beijing University of Agriculture, China; Institut National de la Recherche Agrinomique, France; Chinese Academy of Agricultural Sciences, Beijing, China; Beijing Normal University, China; Huazhong Agriculture University, Wuhan, China; University of Bonn, Germany; Xinjiang Academy of Agricultural Sciences, China; Beijing Novogene Bioinformation Technology Co. Ltd., China; U.S. Department of Agriculture, Charleston, S.C.; USDA Robert W. Holley Center for Agriculture and Health, Ithaca, N.Y.; University of Copenhagen, Denmark.

The project was funded by grants from the Chinese, U.S. and French governments.