Scientists find clues to more disease-resistant watermelons

Are juicier, sweeter, more disease-resistant watermelons on the way? An international consortium of more than 60 scientists from the United States, China, and Europe has published the genome sequence of watermelon (Citrullus lanatus) -- information that could dramatically accelerate watermelon breeding toward production of a more nutritious, tastier and more resistant fruit. The watermelon genome sequence was published in the Nov. 25 online version of the journal Nature Genetics. The researchers discovered that a large portion of disease resistance genes were lost in the domestication of watermelon. With the high-quality watermelon sequence now complete, it is hoped that breeders can now use the information to recover some of these natural disease defenses.

The authors reported that the genome of the domesticated watermelon contained 23,440 genes, roughly the same number of genes as in humans. The group 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.

"Watermelons are an important cash crop and among the top five most consumed fresh fruits; however, cultivated watermelons have a very narrow genetic base, which presents a major bottleneck to its breeding. Decoding the complete genome of the watermelon and resequencing watermelons from different subspecies provided a wealth of information and toolkits to facilitate research and breeding," said Zhangjun Fei, a scientist at the Boyce Thompson Institute for Plant Research at Cornell University, and one of the leaders of this project.

Fei worked with BTI scientists on different aspects of the research, including James Giovannoni, to generate the gene expression data through RNA-sequencing and Lukas Mueller to provide additional analysis to confirm the quality of the genome assembly. Fei also collaborated with Amnon Levi, a research geneticist at the USDA-ARS, U.S. Vegetable Laboratory, Charleston, S.C., on genetic mapping and identifying candidate genes that might be useful to enhance disease resistance in watermelon. The genome sequences of the watermelon are publicly available at the Cucurbit Genomics Database, which is created and maintained by Fei's group.

Believed to have originated in Africa, watermelons were cultivated by Egyptians more than 4,000 years ago, where the fruit was a source of water in dry, desert conditions. They are now consumed throughout the world -- with over 400 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 over 90 percent water, watermelons do contain important nutrients such as vitamins A and C, and lycopene, a compound that gives some fruits and vegetables their red color and appears to reduce the risk of certain types of cancer. Watermelon is also a natural source of citrulline, a non-essential amino acid with various health and athletic performance benefits.

Scientists from Bangalore and Mainz develop new methods for cooling of ions

Among the most important techniques developed in atomic physics over the past few years are methods that enable the storage and cooling of atoms and ions at temperatures just above absolute zero. Scientists from Bangalore and Mainz have now demonstrated in an experiment that captured ions can also be cooled through contact with cold atoms and may thus be stored in so-called ion traps in a stable condition for longer periods of time. This finding runs counter to predictions that ions would actually be heated through collisions with atoms. The results obtained by the joint Indo-German research project open up the possibility of conducting future chemical experiments to generate molecular ions at temperatures as low as those that prevail in interstellar space.

Scientists of the Raman Research Institute in the Bangalore in India and the Institute of Physics at Johannes Gutenberg University Mainz (JGU) in Germany combined two techniques for their experiment. They captured neutral atoms in a magneto-optic trap, cooled them with laser light to a temperature close to absolute zero at minus 273.15 degrees Celsius, and also stored charged particles in an ion trap. For this purpose, Professor Dr. Günter Werth had to set a Paul trap as used in Mainz in India, where it was combined with a magneto-optic trap. It was thus possible to trap ions and cold atoms at one and the same location to observe their development.

"The question was whether it would work at all," explains Werth. The experiment with rubidium ions and rubidium atoms then showed that the particles did actually exchange energy. The ions were effectively cooled during a collision with the cold atoms. As the scientists write in their article in Nature Communications, there are two fundamental processes that determine the outcome. During continuous cooling, the atoms indirectly extract energy from the trapped ions. In addition, the collision between ions and atoms causes both to exchange their charges and results in the transformation of a 'hot' ion into a 'cold' ion. As it is possible to maintain a constant concentration of atoms in the reservoir of the magneto-optic trap, the system has the capacity to cool a larger number of ions without immediate exhaustion of the atom reservoir.

The interaction between ions and atoms is particularly interesting to physicists because it is thought that similar interactions might also occur in the coldness of outer space. "The expectation is that the interaction of ions and atoms at very low temperatures will result in the formation of molecular ions. This is a process that we believe also occurs in inter-stellar space,"