title: Symbiotic mutants deficient in nodule establishment identified after T-DNA transformation of Lotus japonicus.
abstract: Nitrogen-fixing root nodules develop on legumes as a result of an interaction between host plants and soil bacteria collectively referred to as rhizobia. The organogenic process resulting in nodule development is triggered by the bacterial microsymbiont, but genetically controlled by the host plant genome. Using T-DNA insertion as a tool to identify novel plant genes that regulate nodule ontogeny, we have identified two putatively tagged symbiotic loci, Ljsym8 and Ljsym13, in the diploid legume Lotus japonicus. The sym8 mutants are arrested during infection by the bacteria early in the developmental process. The sym13 mutants are arrested in the final stages of infection, and ineffective nodules are formed. These two plant mutant lines were identified in progeny from 1112 primary transformants obtained after Agrobacterium tumefaciens T-DNA-mediated transformation of L. japonicus and subsequent screening for defects in the symbiosis with Mesorhizobium loti. Additional nontagged mutants arrested at different developmental stages were also identified and genetic complementation tests assigned all the mutations to 16 monogenic symbiotic loci segregating recessive mutant alleles. In the screen reported here independent symbiotic loci thus appeared with a frequency of approximately 1.5%, suggesting that a relatively large set of genes is required for the symbiotic interaction.
authors.affiliation: Department of Molecular and Structural Biology, University of Aarhus, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Schauser
authors.forename: K
authors.initials: K
authors.lastname: Handberg
authors.forename: N
authors.initials: N
authors.lastname: Sandal
authors.forename: J
authors.initials: J
authors.lastname: Stiller
authors.forename: T
authors.initials: T
authors.lastname: Thykjaer
authors.forename: E
authors.initials: E
authors.lastname: Pajuelo
authors.forename: A
authors.initials: A
authors.lastname: Nielsen
authors.forename: J
authors.initials: J
authors.lastname: Stougaard
mesh_terms: D003433:Crosses, Genetic; D004251:DNA Transposable Elements; D007887:Fabaceae / Q000235:genetics*; D005816:Genetic Complementation Test; D016296:Mutagenesis; D009154:Mutation; D018517:Plant Roots / Q000235:genetics*; D030821:Plants, Genetically Modified; D010946:Plants, Medicinal; D012230:Rhizobiaceae / Q000235:genetics; D017422:Sequence Analysis, DNA; D013559:Symbiosis / Q000235:genetics*; D014170:Transformation, Genetic
chemical_list: D004251:DNA Transposable Elements