During the mid seventies, there was a search for new model legume symbiotic systems which were characterized by a diploid, small genome, small seeded, transformable plant and the choice fell on Lotus japonicus for the symbiosis giving rise to determinate nodules and Medicago truncatula for the symbiosis giving rise to indeterminate nodules. At the time of the move to Toulouse, he changed systems to the Medicago truncatula-Sinorhizobium meliloti symbiosis since all the laboratories in the Laboratory of Plant-Microbe Interactions worked on this alternative model system.
The aim of the project is to produce a multivolume book on “The Model Legume Medicago truncatula”, consisting of review chapters as well as research chapters describing experiments carried out by the authors with clear materials and methods. These can be updates on previously published papers or new original research. Most of the chapters will use molecular techniques and advanced biochemical analyses to approach a variety of aspects of “The Model Legume Medicago truncatula”. The aim, scope and format of the book is similar to the recently published “Handbook of Molecular Microbial Ecology I and II: Metagenomics…”, the “Molecular Microbial Ecology of the Rhizosphere” and “Biological Nitrogen Fixation” by the same editor, published by Wiley-Blackwell (2011), (2013) and (2015) respectively.
Symbiotical biological nitrogen fixation is an alternative to expensive and environmentally unfriendly chemical nitrogen fertilizer and has been used for years in agriculture. One family of plants, the Leguminosae, has evolved a symbiotic relationship with specific soil bacteria called rhizobia. Once the symbiosis is established and specialized structures (nodules) are formed to house the rhizobia, these fix atmospheric nitrogen and provide it to their legume host plant. In turn, the host plant provides energy to the nitrogen fixing bacteria and the nodulated plants are provided with a distinct advantage over their non-nodulated counterparts.
Legumes include major food and feed crop species, such as soybean pea, clover, chickpea, alfalfa and mungbean. They represent the largest group of angiosperms and are the second group of food and feed crops grown globally. Indeed, they are cultivated on 12-15% of available arable land and are responsible for more than 25% of the world’s primary crop production with 247 million tons of grain legumes produced annually. The legume-rhizobia symbiosis is the most important symbiotic association in terms of biological nitrogen fixation, producing roughly 200 Million Tons of fixed nitrogen annually. A common farming practice is to rotate crop species, with one typically being a legume such as clover or alfalfa. Thus these species are often referred to as “green manure” dramatically improving the organic content and soil volume after the plants are ploughed back into the field.
Model plant species are valuable not only because they lead to basic biology discovery, but also because they provide resources that facilitate translational biology to improve (other) crops of economic importance. Plant scientists are drawn to models because of their ease of manipulation, simple genome organization, rapid life cycles and the availability of multiple other genetic as well as genomic tools.
Medicago truncatula is one of two model legume plants, (the other being Lotus japonicus), which have taken center stage for basic studies, especially those directed at the symbiotic interaction with nitrogen fixing bacteria and phosphorus/nitrogen providing symbiosis with mycorrhizal fungi.
Although initially selected for its symbiotic interaction with S. meliloti andarbuscular mycorrhizae, M. truncatula has many other attributes which benefit from the knowledge obtained and tools developed some of which make this species a model for multiple traits in their own right, which will be covered in these volumes. Although the core of the book will be on the molecular genetics of the symbiotic interactions cited above and described below, the basic biology of M. truncatula and the role of the model system will be described first.
As pointed out above, the development of a legume model system is essential for progress in the field of legume biology and application. This comprehensive book on Medicago truncatula is meant to cover most aspects of M. truncatula biology, biochemistry, genetics and genomics, and therefore to serve as a reference work for those working in the field and those wanting to enter it. Such a book does not presently exist.
