title: Identification of Mesorhizobium loti genes relevant to symbiosis by using signature-tagged mutants.
abstract: Signature-tagged mutagenesis was applied to Mesorhizobium loti, a nitrogen-fixing root-nodule symbiont of the leguminous plant Lotus japonicus. We arranged 1,887 non-redundant mutant strains of M. loti into 75 sets, each consisting of 24 to 26 strains with a different tag in each strain. These sets were each inoculated en masse onto L. japonicus plants. Comparative analysis of total DNA extracted from inoculants and resulting nodules based on quantitative PCR led to the selection of 69 strains as being reduced in relative abundance during nodulation. Plant assays conducted with individual strains confirmed that 3 were defective in nodulation (Nod(-)) and that 10 were Nod(+) but defective in nitrogen fixation (Fix(-)); in each case, the symbiosis deficiency could be attributed to the transposon insertion carried by that strain. Although the remaining 56 strains were Fix(+), 33 of them showed significantly reduced competitiveness during nodulation. Among the mutants we identified are known genes that are diverse in predicted function as well as some genes of unknown function, which demonstrates the validity of this screening procedure for functional genomics in rhizobia.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Sendai 980–8577, Japan.
authors.forename: Naoganchaolu
authors.initials: N
authors.lastname: Borjigin
authors.forename: Keisuke
authors.initials: K
authors.lastname: Furukawa
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Shimoda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Shima
authors.initials: S
authors.lastname: Eda
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Minamisawa
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Mitsui
mesh_terms: D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D014644:Genetic Variation; D000070116:Lotus / Q000378:metabolism; D016254:Mutagenesis, Insertional / Q000379:methods; D009586:Nitrogen Fixation / Q000235:genetics; D055170:Plant Root Nodulation / Q000235:genetics; D012230:Rhizobiaceae / Q000145:classification / Q000235:genetics*; D053204:Root Nodules, Plant / Q000382:microbiology; D013559:Symbiosis / Q000235:genetics