title: Evidence of an American origin for symbiosis-related genes in Rhizobium lusitanum.
abstract: Randomly amplified polymorphic DNA (RAPD) analysis was used to investigate the diversity of 179 bean isolates recovered from six field sites in the Arcos de Valdevez region of northwestern Portugal. The isolates were divided into 6 groups based on the fingerprint patterns that were obtained. Representatives for each group were selected for sequence analysis of 4 chromosomal DNA regions. Five of the groups were placed within Rhizobium lusitanum, and the other group was placed within R. tropici type IIA. Therefore, the collection of Portuguese bean isolates was shown to include the two species R. lusitanum and R. tropici. In plant tests, the strains P1-7, P1-1, P1-2, and P1-16 of R. lusitanum nodulated and formed nitrogen-fixing symbioses both with Phaseolus vulgaris and Leucaena leucocephala. A methyltransferase-encoding nodS gene identical with the R. tropici locus that confers wide host range was detected in the strain P1-7 as well as 24 others identified as R. lusitanum. A methyltransferase-encoding nodS gene also was detected in the remaining isolates of R. lusitanum, but in this case the locus was that identified with the narrow-host-range R. etli. Representatives of isolates with the nodS of R. etli formed effective nitrogen-fixing symbioses with P. vulgaris and did not nodulate L. leucocephala. From sequence data of nodS, the R. lusitanum genes for symbiosis were placed within those of either R. tropici or R. etli. These results would support the suggestion that R. lusitanum was the recipient of the genes for symbiosis with beans from both R. tropici and R. etli.
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Salamanca, Consejo Superior de Investigaciones Científicas (IRNASA-CSIC), Salamanca, Spain.
authors.forename: Angel
authors.initials: A
authors.lastname: Valverde
authors.forename: Encarna
authors.initials: E
authors.lastname: Velázquez
authors.forename: Emilio
authors.initials: E
authors.lastname: Cervantes
authors.forename: José M
authors.initials: JM
authors.lastname: Igual
authors.forename: Peter
authors.initials: P
authors.lastname: van Berkum
mesh_terms: D000569:Americas; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D005798:Genes, Bacterial; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D027805:Phaseolus / Q000382:microbiology*; D055170:Plant Root Nodulation; D011174:Portugal; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D019105:Random Amplified Polymorphic DNA Technique; D012231:Rhizobium / Q000145:classification / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification; D053204:Root Nodules, Plant / Q000382:microbiology; D016415:Sequence Alignment; D012988:Soil Microbiology; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S; C073986:nodS protein, Rhizobiaceae; D008780:Methyltransferases