Construction of High-Density Map, Genome Library, and Saturation Mapping of Nodulation Genes

Abstract

Legumes have a unique characteristic in that they fix atmospheric nitrogen by symbiosis with Rhizobium, vital in maintaining sustainable world agriculture. Legumes are also important crops in their own right, with a high content of seed proteins with a good balance of amino acids among them (Sarwar et al. 1978). Lotus japonicus as a model legume is attracting the attention of researchers because of its high transformation susceptibility (Thykajaer et al. 1995), and a relatively small genome size (475 MB, Kawasaki and Murakami 2000; Murakami and Kawasaki, submitted). From the standard accession Gifu (G129) several mutant libraries have been constructed for use in functional genomics (Szczyglowski et al. 1998; Kawaguchi et al. 2002). The most interesting topic in its regard is no doubt the genetic dissection of the nodulation process, including that of the related mycorrhizal development. If essential components of the process can be clarified, transferring the ability of the nitrogen fixation to other important crops, including the graminaceous family, would be a great blessing for world agriculture and for environment protection. However, the current status of infrastructures for genomics in Lotus japonicus is still far behind those of Arabidopsis and rice, whose genomes have been sequenced completely (The Arabidopsis Genome Initiative 2000; Goff et al. 2002; Yu et al. 2002).