Production and characterization of diverse developmental mutants of Medicago truncatula

The diploid annual legume Medicago truncatula has been developed as a tract able genetic system for studying biological questions that are unique to, o r well suited for study in legume species. An efficient mutagenesis protoco l using ethyl-methyl sulfonate and a polymorphic ecotype with properties ap propriate for use as a mapping parent are described. Isolation and characte rization of three developmental mutants are described. The mtapetala mutati on results in homeotic conversions of floral organ whorls 2 and 3 into sepa ls and carpelloid structures, respectively, similar to mutations in the ape tala3/pistillata genes of Arabidopsis. The palmyra mutation primarily affec ts seedling shoot meristem initiation, and thus phenocopies meristem functi on mutations identified in Arabidopsis such as the zwille locus. The phenot ype of the palmyra and mtapetala double mutant is additive, with seedling s hoot meristems and floral organs indistinguishable from those of the single palmyra and mtapetala mutants, respectively. These results are consistent with a lack of genetic interaction between these loci. A third mutant, spec kle, is characterized by spontaneous necrotic lesion formation on leaves, r oot, and stems, similar to necrosis mutants identified in other plant speci es. In addition to documenting the efficient mutagenesis of M. truncatula, the availability of developmental mutants that phenocopy characterized Arab idopsis mutants will provide a basis for establishing orthologous gene func tion between M. truncatula and Arabidopsis, once the genes responsible are cloned. Moreover, the male-sterile, female-fertile nature of the mtapetala mutant provides a convenient tool for genetic analyses in M. truncatula.