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. Common bean (Phaseolus vulgaris)is an important agricultural leguminous crop that has the ability to nodulate with rhizobia from at least 20 different host plant genera (summarized in reference 1). Among bean-nodulating rhizobia, the host range varies from narrow, as is the case for Rhizobium etli strain CFN42 (13), to wide, as for example the Rhizobium tropici IIA and IIB strains CFN299 and CIAT899 (14). Wide host range in bean-nodulating rhizobia was defined as the ability to form a symbiosis with the tropical tree Leucaena leucocephala (14) requiring the R. tropici nodS gene downstream of nodC (32). In complementation analysis, the R. tropici nodS gene was shown to extend the host range of R. etli to include L. leucocephala (32).According to Graham and Ranalli (6), common bean was introduced as a curiosity from the Americas into Europe via the Iberian Peninsula during the 16th century (34), but today it is a widely cultivated crop in Spain (21) and Portugal (19). Descriptions of bean rhizobia from the Iberian Peninsula have been made with isolates that originated from soils of Spain (8,20) and Portugal (25). The majority of the isolates originating from Spain were characterized as R. etli, R. gallicum, and R. giardinii (8,20), probably imported from the Americas (4, 14, 23, 35) along with the seeds (16). However, the isolates of Portuguese origin were proposed to represent the new species R. lusitanum, having characters that are different from ...

Identification at the species and symbiovar levels of strains nodulating Phaseolus vulgaris in saline soils of the Marrakech region (Morocco) and analysis of the otsA gene putatively involved in osmotolerance

“…Since the symbiovar phaseoli was not found in the R. gallicum strains isolated in Mesoamerica [49] and considering that this symbiovar evolved with R. etli, it is possible that the transfer of As for the group of strains identified as R. tropici, RHM14 and RHM54, they were identical to the Moroccan strain RP261 [31] and to several American strains from R. tropici and from R. leucaenae (Figure 4). They were also identical to nodC of R. lusitanum type strain, a Portuguese species nodulating common bean that probably acquired its nodC gene from R. leucaenae, since this last species has been found in common bean nodules in Portugal and carries identical nodC gene [55]. Therefore the American origin of the R. tropici strains nodulating P. vulgaris in Morocco seems to be clear in agreement with the suggestions of Diouf et al [10].…”

“…Initially this species included two groups, A and B, but recently the strains from group A have been reclassified into a new species named R. leucaenae [38]. It is interesting to highlight that curiously the strains isolated in Morocco belong to R. tropici [31], whereas those found in Europe belong to R. leucaenae [21,55]. This can be due to a better adaptation of each one of these species to different environmental conditions including the local varieties of common bean in each site.…”

“…For example, P. vulgaris is not considered a promiscuous legume because it can be nodulated by several chromosomal species of rhizobia, but rather because it nodulates with many different symbiovars (which harbour different nodC genes). In this way, common bean is commonly nodulated by symbiovars phaseoli, gallicum, giardinii, mediterranense [44] and by strains from other groups that belong to undefined symbiovars [55]. Among these symbiovars, only sv phaseoli seems to be exclusive for common bean nodulation [3,55] and therefore the symbiovar phaseoli plasmid should have evolved with native common bean plants in America [1,24].…”

Diversity of Rhizobia Nodulating Faba Bean (Vicia faba) Growing in Egypt

“…Also, it is in agreement with who tested 28 of indigenous rhizobia nodulating chickpea in India using RFLP to classify their isolates and who found that all RAPD primers detected one or more polymorphic DNA fragments among the studied rhizobia species and that RAPD is a very discriminative and efficient method for differentiating and studying genetic diversity of Rhizobium. Also, Valverde, et al (2011) found that RAPD fingerprint patterns were able to distinguish genomic variation within members of the same species of Rhizobium [33][34][35].…”

Cicer canariense, an endemic legume to the Canary Islands, is nodulated in mainland Spain by fast-growing strains from symbiovar trifolii phylogenetically related to Rhizobium leguminosarum

“…Therefore, C. arietinum establishes endosymbiosis with several Mesorhizobium species; nevertheless, it is a restrictive legume because all the strains nodulating chickpea belong to the symbiovar ciceri [21,30,42]. Moreover, all strains nodulating chickpea isolated from different continents have been shown to harbor closely related nodC genes, including those isolated in Syria and Turkey, the distribution centers of chickpea [33], which suggests a dispersion of chickpea endosymbionts together with its seeds, as already reported for other legumes such as Phaseolus [8,10,27,37] or Vicia [3]. Chickpea seeds may have dispersed strains from their distribution centers that harbored the typical nodulation genes of symbiovar ciceri, acquired through horizontal transfer from several Mesorhizobium species in Africa, Asia and Europe, where the nodC genes are highly conserved across Mesorhizobium strains nodulating chickpea [21].…”