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Root, Root Hair, and Symbiotic Mutants of the Model Legume Lotus japonicus

¹Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902 Japan; ²National Institute of Agrobiological Resources, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602 Japan; ³Iwate Biotechnology Research Center, Narita 22-174-4, Kitakami, Iwate 024-0003 Japan; ⁴Science University of Tokyo, 2641 Yamazaki, Noda-shi, Chiba 278-8510 Japan; ⁵Nihon Women's University, Mejirodai 2-8-1, Bunkyo-ku, Tokyo 112-8681 Japan; ⁶PRESTO, Japan Science and Technology Corporation

To gain an overview of plant factors controlling nodule number and organogenesis, an extensive screening using model legume Lotus japonicus was carried out. This screening involved 40,000 M2 seeds, and 32 stable mutant lines were isolated. From these, 16 mutant lines maintaining the phenotypic variation were selected and genetically analyzed. With respect to nodule number, four loci were identified, Ljsym77, Ljsym78, slippery root (slp), and radial organization1 (rdo1). The former two mutants have an increased number of nodules, while the latter two have a decreased number. Ljsym78-1 and Ljsym78-2 are hypernodulating mutants with a branched root system and were found to be allelic to Ljsym16. The phenotype of the Ljsym77 mutant was highly pleiotropic, being deficient in light and gravity responses. The slp mutant was isolated as a low-nodulating mutant lacking root hairs. Concerning nodule organogenesis, nine symbiotic loci were identified, including the two loci alb1 and fen1. Mutants affecting the developmental process of nodule organogenesis were placed in three phenotypic categories: Nod¯ (Ljsym70 to Ljsym73), Hist¯ (alb1-1, alb1-2, and Ljsym79), and Fix¯ (fen1, Ljsym75, and Ljsym81).

Additional keywords: root development.