Analysis of Rhizobium etli and of its symbiosis with wild Phaseolus vulgaris supports coevolution in centers of host diversification

Abstract

Common beans (Phaseolus vulgaris) comprise three major geographic genetic pools, one in Mexico, Central America, and Colombia, another in the southern Andes, and a third in Ecuador and northern Peru. Species Rhizobium etli is the predominant rhizobia found symbiotically associated with beans in the Americas. We have found polymorphism in the common nodulation gene nodC among R. etli strains from a wide range of geographical origins, which disclosed three nodC types. The different nodC alleles in American strains show varying predominance in their regional distributions in correlation with the centers of bean genetic diversification (BD centers). By cross-inoculating wild common beans from the three BD centers with soils from Mexico, Ecuador, Bolivia, and Northwestern Argentina, the R. etli populations from nodules originated from Mexican soil again showed allele predominance that was opposite to those originated from Bolivian and Argentinean soil, whereas populations from Ecuadorian soil were intermediate. These results also indicated that the preferential nodulation of beans by geographically related R. etli lineages was independent of the nodulating environment. Coinoculation of wild common beans from each of the three BD centers with an equicellular mixture of R. etli strains representative of the Mesoamerican and southern Andean lineages revealed a host-dependent distinct competitiveness: beans from the Mesoamerican genetic pool were almost exclusively nodulated by strains from their host region, whereas nodules of beans from the southern Andes were largely occupied by the geographically cognate R. etli lineages. These results suggest coevolution in the centers of host genetic diversification.Phaseolus vulgaris-rhizobia coevolution ͉ Rhizobium etli lineages ͉ symbiotic interaction ͉ nodC gene

Genetic and phenotypic diversity of Rhizobium isolates from Southern Ecuador

“…Although few studies have reported on the genetic diversity of Rhizobium in Ecuador (Ribeiro et al, 2013), this is the first report of species diversity in the southern region of the country. Similar to this study, R. etli, R. leguminosarum and R. tropici have been previously isolated from common bean nodules (Martínez-Romero, 2003;Aguilar;Riva;Peltzer, 2004;Oliveira et al, 2011) and are considered to be the predominant occupant species of bean nodules in the Andean region (Junier et al, 2014;Ribeiro et al, 2015). Ecuador, north of Peru, Colombia and the Andean Region are currently considered to be the centers of domestication/diversity of the common bean (Oliveira et al, 2011).…”

A Small GTPase of the Rab Family Is Required for Root Hair Formation and Preinfection Stages of the Common Bean–RhizobiumSymbiotic Association

“…These strains are representative lineages of the geographic regions corresponding to the two common bean domestication centers, Mesoamerican and Andean. According to our previous findings, common bean is preferentially and more efficiently nodulated by R. etli strains that coevolved in the same geographic region (Aguilar et al, 2004;Peltzer Meschini et al, 2008). Upon rhizobial inoculation, RabA2 mRNA levels increased in the entire root and to a higher extent in A phylogenetic tree of Arabidopsis Rab proteins and RHS24-03 (arrow) was generated using MEGA4 from a ClustalW alignment (available as Supplemental Data Set 1 online).…”

“…These strains were chosen as representatives of the main polymorphic forms of the nodC gene associated with domestication centers of common bean (Aguilar et al, 2004). Despite the fact that RabA2 was obtained in a screening as differentially expressed in root hairs treated with either of these strains, overexpression of RabA2 did not change the strain preference previously reported (Peltzer Meschini et al, 2008) or have any noticeable effect on nodulation.…”

“…Rhizobium etli strains SC15 and 55N1 were previously reported (Aguilar et al, 2004). Agrobacterium rhizogenes strain K599 (Bond and Gresshoff, 1993) and the same strain carrying the p35S:GFPGUS+ construct were kindly provided by Federico Sá nchez (Universidad Nacional Autó noma de Mé xico, Cuernavaca, Mé xico).…”

Identification of Bacterial Groups Preferentially Associated with Mycorrhizal Roots of Medicago truncatula

“…This is in agreement with the significant differences recorded between the genetic structure and the diversity of the bacterial communities associated with the two uncultivated soils (data not shown). This hypothesis of coevolution in centers of host diversification between plants and associated soil-borne microorganisms has recently been proposed when analyzing Rhizobium etli diversity and its symbiosis with Phaseolus vulgaris (1). Besides their origins, the two soils also differ in their levels of fertility.…”