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Sequence and Mutational Analysis of the 6.7-kb Region Containing nodAFEG Genes of Rhizobium sp. Strain N33: Evidence of DNA Rearrangements

¹Recherche en sciences de la vie et de la santé, Pavillon Charles-Eugène Marchand, Université Laval, Québec (Québec), Canada G1K 7P4; ²Centre de recherche et de développement sur les sols et les grandes cultures, Agriculture et Agroalimentaire Canada, 2560, boul. Hochelaga, Sainte-Foy (Québec), Canada G1V 2J3

A 6.7-kb region upstream of nodBC genes in Rhizobium sp. strain N33 was shown to contain the nodAFEG genes and an open reading frame designated orfZ. The open reading frames for these genes contain 591, 282, 1209, 738, and 1,338 nucleotides respectively. Homologues of these genes were found in other rhizobia with the exception of orfZ, for which there was no counterpart found in the GenBank/EMBL database. Tn5 mutagenesis in nodEG and in the intergenic nodG-B region has shown a Nod⁺ phenotype on their temperate hosts Onobrychis viciifolia and Astragalus cicer. The nodules formed on O. viciifolia plants by these mutants were altered in shape and size. However, on A. cicer there was only a reduction in the number of nodules formed, compared with the wild-type strain. Sequence analysis of the orfZ-nodA and nodG-B intergenic regions indicates the presence of truncated nodD genes.

Additional keywords: nodulation, symbiosis.