Science - November 18, 2011

Refuted hypothesis gets into Nature

René Geurts tested a hypothesis about the evolution of nitrogen fixation in leguminous plants. The hypothesis was refuted but still made it into Nature.

The alfalfa species Medicago truncatula is a long-established model crop for genetic research.
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Geurts does research on the symbiotic cooperation between leguminous plants and rhizome bacteria on the supply of nitrogen for the plants. Plant scientists have been trying to figure out the mechanism behind this symbiosis for a century.  
Together with international colleagues, Geurts mapped the genome of the alfalfa species Medicago truncatula. ‘The genome of soya was sequenced a year ago and we know a lot about the genome of the lotus, which is a legume too. Now we compared these three leguminous plant species with non-leguminous plants, in terms of genetics. This entailed testing a hypothesis of mine, which suggests that specific gene duplications underlie the evolution of the nitrogen-binding Rhizobial symbiosis’, says Geurts.

‘We know that a genome duplication took place 60 million years ago in the ancestors of the legumes and my hunch was that nitrogen fixation came into existence then. We looked for the mechanism in duplicate gene clusters’, says Geurts. ‘These do exist and they also contributed to the evolution of the Rhizobial symbiosis, but they are not its origin. Bang goes my hypothesis’. Nature published the results on 16 November.
 
Geurts now plans to approach the research from another angle. He is going to have the genome of the Parasponia tree from New Guinea mapped. This is the only non-leguminous plant that has developed Rhizobial symbiosis. Geurts wants to compare the genome of the symbiotic Parasponia with that of a close relative. ‘I expect the genetic differences to be small. By doing this we hope to get more precise pointers.’
Geurts does research on the symbiotic cooperation between leguminous plants and rhizome bacteria on the supply of nitrogen for the plants. Plant scientists have been trying to figure out the mechanism behind this symbiosis for a century.  
 
Together with international colleagues, Geurts mapped the genome of the alfalfa species Medicago truncatula. 'The genome of soya was sequenced a year ago and we know a lot about the genome of the lotus, which is a legume too. Now we compared these three leguminous plant species with non-leguminous plants, in terms of genetics. This entailed testing a hypothesis of mine, which suggests that specific gene duplications underlie the evolution of the nitrogen-binding Rhizobial symbiosis', says Geurts.

'We know that a genome duplication took place 60 million years ago in the ancestors of the legumes and my hunch was that nitrogen fixation came into existence then. We looked for the mechanism in duplicate gene clusters', says Geurts. 'These do exist and they also contributed to the evolution of the Rhizobial symbiosis, but they are not its origin. Bang goes my hypothesis'. Nature published the results on 16 November.
Geurts now plans to approach the research from another angle. He is going to have the genome of the Parasponia tree from New Guinea mapped. This is the only non-leguminous plant that has developed Rhizobial symbiosis. Geurts wants to compare the genome of the symbiotic Parasponia with that of a close relative. 'I expect the genetic differences to be small. By doing this we hope to get more precise pointers.' 
 

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