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Nodule Organogenesis and Symbiotic Mutants of the Model Legume Lotus japonicus

July 1998 , Volume 11 , Number  7
Pages  684 - 697

Krzysztof Szczyglowski , 1 Robert S. Shaw , 1 , 2 Judith Wopereis , 1 Sue Copeland , 1 Dirk Hamburger , 1 Beth Kasiborski , 1 Frank B. Dazzo , 3 and Frans J. de Bruijn , 1 , 3 , 4

1Department of Energy Plant Research Laboratory, 2Department of Botany and Plant Pathology, 3Department of Microbiology, 4Genetics Program, Michigan State University, East Lansing 48824-1312, U.S.A.

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Accepted 28 March 1998.

A detailed microscopical analysis of the morphological features that distinguish different developmental stages of nodule organogenesis in wild-type Lotus japonicus ecotype Gifu B-129-S9 plants was performed, to provide the necessary framework for the evaluation of altered phenotypes of L. japonicus symbiotic mutants. Subsequently, chemical ethyl methanesulfonate (EMS) mutagenesis of L. japonicus was carried out. The analysis of approximately 3,000 M1 plants and their progeny yielded 20 stable L. japonicus symbiotic variants, consisting of at least 14 different symbiosis-associated loci or complementation groups. Moreover, a mutation affecting L. japonicus root development was identified that also conferred a hypernodulation response when a line carrying the corresponding allele (LjEMS102) was inoculated with rhizobia. The phenotype of the LjEMS102 line was characterized by the presence of nodule structures covering almost the entire root length (Nod++), and by a concomitant inhibition of both root and stem growth. A mutation in a single nuclear gene was shown to be responsible for both root and symbiotic phenotypes observed in the L. japonicus LjEMS102 line, suggesting that (a) common mechanism(s) regulating root development and nodule formation exists in legumes.

© 1998 The American Phytopathological Society