1Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan; 2Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan; 3National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan
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Accepted 2 January 2006.
Legume plants develop specialized root organs, the nodules, through a symbiotic interaction with rhizobia. The developmental process of nodulation is triggered by the bacterial microsymbiont but regulated systemically by the host legume plants. Using ethylmethane sulfonate mutagenesis as a tool to identify plant genes involved in symbiotic nodule development, we have isolated and analyzed five nodulation mutants, Ljsym74-3, Ljsym79-2, Ljsym79-3, Ljsym80, and Ljsym82, from the model legume Lotus japonicus. These mutants are defective in developing functional nodules and exhibit nitrogen starvation symptoms after inoculation with Mesorhizobium loti. Detailed observation revealed that infection thread development was aborted in these mutants and the nodules formed were devoid of infected cells. Mapping and complementation tests showed that Ljsym74-3, and Ljsym79-2 and Ljsym79-3, were allelic with reported mutants of L. japonicus, alb1 and crinkle, respectively. The Ljsym82 mutant is unique among the mutants because the infection thread was aborted early in its development. Ljsym74-3 and Ljsym80 were characterized as mutants with thick infection threads in short root hairs. Map-based cloning and molecular characterization of these genes will help us understand the genetic mechanism of infection thread development in L. japonicus.
© 2006 The American Phytopathological Society