Genome map of legume reveals how ancient gene duplication led to plants' unique properties

The team, led by University of Minnesota plant scientist Nevin Young, recently completed the multiyear effort to map the genome of Medicago truncatula, which scientists use as a model to understand the biology of legumes like soybeans, alfalfa and peas. The project’s goal, Young says, was to document how symbiosis – the process that legumes like Medicago use to create their own nitrogen fertilizer through association with special bacteria – evolved.

The team of scientists found that Medicago’s symbiosis can be traced to the time when dinosaurs disappeared from the Earth. Apparently, Medicago experienced a massive genome duplication leading to novel pairs of genes essential for symbiosis, says Young. The team found that ancient genes split into pairs that separately control complementary forms of symbiosis, enabling the modern form of nitrogen fixation that makes legumes so central in agricuture. For biologists, this phenomenon is known as "genetic sub-functionalization" and is considered an important scientific theory about how novel genes evolve in both plants and animals.

‘?While Medicago truncatula is not grown as a food crop itself, it is very closely related to alfalfa and other edible legumes. Symbiosis in legumes is the world’s largest source of natural soil fertilizer, so if plant breeders could enhance legume symbiosis – or even introduce it into other food crops – farmers would save money and reduce the environmental impact of applied fertilizers. The recent discoveries about symbiosis revealed through the sequencing of Medicago’s genome could be invaluable as scientists try to increase global food production to feed an ever expanding population.

“The Medicago genome sequence will be an essential reference for both applied plant breeders and basic scientists. The insights we’ve gained into the evolution of symbiosis demonstrate the power of plant genomics to reveal fascinating biological processes,” says Young.

Major U.S. research funding for mapping the Medicago truncatula genome was provided by the National Science Foundation and the Noble Foundation.

While the project was coordinated at the University of Minnesota, it involved many partner institutions, including the University of Oklahoma; J. Craig Venter Institute; Genoscope; the Wellcome Trust Sanger Institute; CNRS/INRA-Toulouse; John Innes Centre; Noble Foundation; University of Wageningen; MIPS-Munich; Ghent University; and the National Center for Genome Resources. The paper has 124 co-authors at 31 institutions in 8 countries.

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• Last modified on November 16, 2011