Diversification of Lupine Bradyrhizobium Strains: Evidence from Nodulation Gene Trees

Abstract

Bradyrhizobium strains isolated in Europe from Genisteae and serradella legumes form a distinct lineage, designated clade II, on nodulation gene trees. Clade II bradyrhizobia appear to prevail also in the soils of Western Australia and South Africa following probably accidental introduction with seeds of their lupine and serradella hosts. Given this potential for dispersal, we investigated Bradyrhizobium isolates originating from a range of native New World lupines, based on phylogenetic analyses of nodulation (nodA, nodZ, noeI) and housekeeping (atpD, dnaK, glnII, recA) genes. The housekeeping gene trees revealed considerable diversity among lupine bradyrhizobia, with most isolates placed in the Bradyrhizobium japonicum lineage, while some European strains were closely related to Bradyrhizobium canariense. The nodA gene tree resolved seven strongly supported groups (clades I to VII) that correlated with strain geographical origins and to some extent with major Lupinus clades. All European strains were placed in clade II, whereas only a minority of New World strains was placed in this clade. This work, as well as our previous studies, suggests that clade II diversified predominately in the Old World, possibly in the Mediterranean. Most New World isolates formed subclade III.2, nested in a large "pantropical" clade III, which appears to be New World in origin, although it also includes strains originating from nonlupine legumes. Trees generated using nodZ and noeI gene sequences accorded well with the nodA tree, but evidence is presented that the noeI gene may not be required for nodulation of lupine and that loss of this gene is occurring.

Rhizobial communities in symbiosis with legumes: genetic diversity, competition and interactions with host plants

“…Moreover, frequent genetic transfer and recombination events were evidenced within species (between sublineages) in different models [11,36,42,43,49,101]. There is an agreement, that (a) in numerous cases the world distribution of microsymbiont strains followed the distribution of their hosts, and the symbiosis-associated part of the genome (localized on symbiotic plasmid or symbiotic island) was subjected to the most intense evolution and fitting [103,104,106,107], and (b) other (non-symbiotic) parts of the rhizobial genome changed together with the symbiosis-related regions [105,108]. Genetic analyses of microsymbiont populations isolated from different but closely related legumes support the hypothesis of coevolution in Rhizobium-legume symbiosis, which takes place in centers of genetic diversification of plant hosts [109][110][111].…”

Phylogenetic Diversity and Symbiotic Effectiveness of Root-Nodulating Bacteria Associated with Cowpea in the South-West Area of Japan

“…For example, the predominant root-nodule bacteria of Genistioid legumes are mostly B. japonicum and B. canariense, while Milletioid legumes appear to be more commonly nodulated by B. yuanmingense and B. elkanii (27). Krasova-Wade et al This is the first report describing the isolation of a betaproteobacterial strain (Ralstonia sp.…”

The genus Micromonospora is widespread in legume root nodules: the example of Lupinus angustifolius

“…Plants of the genus Lupinus, which accomodates around 250 species of herbs and shrubs distributed in the Mediterranean area and in the American continent, are nodulated by Bradyrhizobium spp. (Jarabo-Lorenzo et al, 2003;Vinuesa et al, 2005;Stepkowski et al, 2007).…”