Several genomic tools and resources are already available for M. truncatula. Funding from NSF and the Noble Foundation has resulted in an extensive database of over 226,000 M. truncatula ESTs and an ongoing genome sequencing project to be completed by 2007 (www.medicago.org/genome). Gene expression, protein and metabolite profiling tools are also available for M. truncatula (www.noble.org/medicago). In spite of all these genomic resources, it is still a daunting task to determine gene function. Extensive collections of M. truncatula mutants are needed to address gene function. Currently there are no large, publicly available collections of M. truncatula mutants. With the M. truncatula genome sequencing project approaching completion, availability of a large collection of insertion mutants will be vital for M. truncatula to become a more powerful model organism.

In collaboration with Dr. Pascal Ratet, CNRS, France, we have developed a fast and efficient gene tagging system for M. truncatula which will be an invaluable resource for legume functional genomics. The main objective of this project is to do a near-saturation mutagenesis of Medicago truncatula using a tobacco retrotransposon Tnt1. Development of Tnt1 insertion lines will help M. truncatula to become a more useful model species to understand legume biology. Information and materials generated from this project will be made freely available to the scientific community.

So far, we have generated more than 3,000 Tnt1 tagged M. truncatula lines with an average of 20 insertions per line. In an initial international forward genetics screening effort of our 922 lines, we identified visible mutants in 25 distinct classes, including nodulation, mycorrhizal colonization, vegetative development, and flowering time. We show a very high mutation frequency of approximately 30 percent visible phenotype in the R1 progenies demonstrating that Tnt1 tagging is a very efficient system for genome-wide saturation mutagenesis in M. truncatula. Collaborative efforts are underway to generate a sizable number of tagged mutant lines in the next five years and also to develop a flanking sequence database for reverse genetics studies.

If you are interested in participating in our annual mutant screening event, please contact Dr. Kiran Mysore.

Publications related to this project:
Tadege, M., Ratet, P. and Mysore, K.S. 2005. Insertional mutagenesis: a Swiss Army Knife for functional genomics of Medicago truncatula. Trends in Plant Science, 10:229-235.