A Mesorhizobium loti mutant with reduced glucan content shows defective invasion of its host plant Lotus japonicus.
Random transposon mutagenesis led to the isolation of a novel Mesorhizobium loti mutant that is defective in nitrogen fixation during symbiosis with Lotus japonicus. The mutated locus, designated cep, encodes a putative cell-envelope protein displaying no significant sequence similarity to proteins with known functions. This mutant elicits the formation of nodule-like bumps and root-hair curling, but not the elongation of infection threads, on L. japonicus roots. This is reminiscent of the phenotypes of rhizobial mutants impaired in cyclic beta-glucan biosynthesis. The cep mutant exhibits partially reduced content of cell-associated glucans and intermediate deficiency of motility under hypo-osmotic conditions as compared to a glucan-deficient mutant. Second-site pseudorevertants of the cep mutant were isolated by selecting for restoration of symbiotic nitrogen fixation. A subset of pseudorevertants restored both symbiotic capability and glucan content to levels comparable to that of the wild-type. These results suggest that the Cep product acts on a successful symbiosis by affecting cell-associated glucan content.
Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
Yasuyuki
Y
Kawaharada
Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
Shima
S
Eda
Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
Kiwamu
K
Minamisawa
Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
Hisayuki
H
Mitsui
D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D020561:Alphaproteobacteria / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity* / Q000502:physiology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D005936:Glucans / Q000378:metabolism*; D000070116:Lotus / Q000382:microbiology*; D016254:Mutagenesis, Insertional; D009154:Mutation; D009586:Nitrogen Fixation / Q000235:genetics*; D010641:Phenotype; D018517:Plant Roots / Q000382:microbiology; D013559:Symbiosis / Q000235:genetics*
D001425:Bacterial Outer Membrane Proteins; D004251:DNA Transposable Elements; D005936:Glucans; D000469:Alkaline Phosphatase