Structural and Comparative Genome Analysis of Lotus japonicus

Legumes, the third largest family of flowering plants, are composed of more than 18,000 species with diverse characteristics, and many of the species are of agronomic importance. They have long been the targets of breeding programs and, in this regard, genomics may provide the greatest potential for benefit. Legume genomics in two model plants, Lotus japonicus and Medicago truncatula, has advanced rapidly over the past few years (Young et al., 2005; Sato and Tabata, 2006). L. japonicus is a perennial temperate pasture species with characteristics suitable for genetic and genomic studies, such as short life cycle (2–3 months), self-fertility, diploidy (n = 6), small genome size (472.1 Mb), and feasibility of genetic transformation. Genomics in L. japonicus was initiated in 1999 by collection of ESTs (Asamizu et al., 2004), followed by large-scale genome sequencing (Sato et al., 2001), generation of DNA markers and construction of high-density genetic linkage maps (Hayashi et al., 2001). The information and material resources accumulated during the course of these genomic analyses are useful for understanding the genetic system of L. japonicus. Furthermore, such resources might assist breeding programs by comparison and subsequent transfer of the knowledge on L. japonicus to crop legumes (Zhu et al., 2005).