Tnt1 Insertional Mutagenesis in Medicago truncatula.

Legumes play irreplaceable roles in sustainable agriculture due to their unique capability of fixing gaseous nitrogen in the atmosphere and turning into plant-usable ammonium through interaction with rhizobia. With the completion of genome sequencing of several model and non-model legumes, it is highly desirable to generate mutant populations for characterizing gene functions in genome-wide scales. In the past decade, we have generated a near-saturated insertional mutant population in the model legume Medicago truncatula using the tobacco-derived Tnt1 retrotransposon at Noble Research Institute. The mutant population was generated through callus induction, subculture, and regeneration from a starting transgenic line harboring three homozygous copies of Tnt1 insertion. The population consists of 21,700 regenerated lines that encompass more than 500,000 Tnt1 insertions. Based on the genome size, average gene length, and random insertion nature of Tnt1, this mutant population covers about 90% of genes in the M. truncatula genome. Due to the convenience of known Tnt1 sequence, the mutant population is highly feasible for both forward and reverse genetics. Over the past 12 years, we have distributed more than 9000 mutant lines to 203 research groups in 24 countries.