Introduction of an Early Flowering Accession “Miyakojima” MG-20 to Molecular Genetics in Lotus japonicus

Abstract

Leguminosae is the third largest family of the angiosperms. The family includes the remarkable biodiversity ranging over the levels of the morphology, secondary metabolites, seed proteins, and biological interactions with insects and others. The family also includes many important plants closely related to human life. However, genes responsible for the causing generation of leguminous biodiversity and usefulness have not been elucidated at the molecular level. In order to identify and characterize such genes—for example, genes controlling symbiotic nitrogen fixation with rhizobia—certain model legumes that enable progress in molecular genetics are definitely required. In general, transformation of leguminous plants is more difficult than experimentally common plants such as Arabidopsis and tobacco. Two herbaceous plants of Lotus japonicus and Medicago truncatula have emerged from the beginning of 1990s as transformable diploid legumes (Barker et al. 1990; Handberg and Stougaard 1992). L. japonicus is known as a determinate-type nodulation plant like soybean and develops slender legumes. On the other hand, M. truncatula is known as an indeterminate-type nodulation plant such as pea and vetch and forms spiral legumes. L. japonicus has six chromosomes (Kawakami 1930) and a small genome size (442Mb per haploid of a widely used accession “Gifu” B-129) (Ito et al. 2000). The generation time is 3–4 months and up to 6,000 seeds can be obtained from one plant (Handberg and Stougaard 1992).