Legumics

Legume plants are used in agriculture as a protein source for human and animal nutrition and may represent the unique protein source for human nutrition in some countries. The high protein content of legume plants is achieved via the establishment of a root symbiosis with nitrogen fixing rhizobia. Establishment of this symbiotic interaction occurs when the soil nitrogen source is limiting and results in the formation of a dedicated root organ called the root nodule inside which rhizobia fix nitrogen. The development of the legume root system is not only determined by their ability to interact with symbiotic microorganisms but also by the distribution and number of lateral roots. In order to adapt their root architecture to cope with nutrient starvation and abiotic stresses, legumes have developed specific strategies, which are likely different from those of the reference plant A. thaliana which is unable to develop symbiotic interactions. Interestingly, several lines of evidence indicate that nodules and lateral roots formations are integrated into regulatory mechanisms affecting the whole root system in response to environmental changes. Thus, the use of legumes in modern agriculture will require understanding various aspects of legume development such as the symbiotic interaction with rhizobia, that can be used to reduce nitrogen input to the culture, but also root architecture that will condition access to nutrients. Model plant organisms proved to be useful to answer biological questions that are more difficult to study in cultivated species. Medicago truncatula is recognized as an excellent legume model in view of its small, diploid genome, self-fertility, and short life cycle, as well as availability of various genomic and genetic tools. We now know that genetic and genomic tools developed for this plant can be readily applied to the important crop species such as alfalfa, pea and Faba bean as the result of their close genome relationship. This gives the opportunity to directly apply results obtained with this plant to legume crops. The use of tagged mutant collections is essential to reveal gene functions and to uncover the genetic interactions such as those that underlie plant responses to the environment and development. For example, genetic studies based on tagged mutant collections have been extensively used in Arabidopsis and sequencing of the T-DNA insertion sites in mutant collections and availability of this information as a web resource represents a very important tool for the scientific community. An insertion mutant collection based on the use of retroelements Tnt1 and MERE1 was developed in M. truncatula during the EU GLIP project (www.eugrainlegumes.org) in parallel to the one existing at the Noble foundation (http://bioinfo4.noble.org/mutant/), but in the case of the GLIP collection, only the construction of the collection was financed despite the value of such collections for the community. The purpose of this French/Hungarian ANR academic project is to further develop and use the genomic resources established for the model legume M. truncatula. For this, we propose to use the insertion mutant collections developed in the frame of the FP6 Grain Legume Project in order to i) develop a high throughput sequencing method for sequencing the insertion sites in a large number of the existing insertion mutant lines, ii) apply this technology to sequence the majority of the tagged loci in a large part of this mutant collection iii) perform genetic screens in order to identify mutants affected in nodule functioning and root development, iv) use the sequence information to identify the tagged genes in these mutants and v) characterize at the molecular, physiological and cellular levels some of the identified mutants.