Abstract
Rhizobium leguminosarum bv. trifolii TA1 (RtTA1) is a soil bacterium establishing a highly specific symbiotic relationship with clover, which is based on the exchange of molecular signals between the host plant and the microsymbiont. The RtTA1 genome is large and multipartite, composed of a chromosome and four plasmids, which comprise approximately 65 % and 35 % of the total genome, respectively. Extrachromosomal replicons were previously shown to confer significant metabolic versatility to bacteria, which is important for their adaptation in the soil and nodulation competitiveness. To investigate the contribution of individual RtTA1 plasmids to the overall cell phenotype, metabolic properties and symbiotic performance, a transposon-based elimination strategy was employed. RtTA1 derivatives cured of pRleTA1b or pRleTA1d and deleted in pRleTA1a were obtained. In contrast to the in silico predictions of pRleTA1b and pRleTA1d, which were described as chromid-like replicons, both appeared to be completely curable. On the other hand, for pRleTA1a (symbiotic plasmid) and pRleTA1c, which were proposed to be unessential for RtTA1 viability, it was not possible to eliminate them at all (pRleTA1c) or entirely (pRleTA1a). Analyses of the phenotypic traits of the RtTA1 derivatives obtained revealed the functional significance of individual plasmids and their indispensability for growth, certain metabolic pathways, production of surface polysaccharides, autoaggregation, biofilm formation, motility and symbiotic performance. Moreover, the results allow us to suggest broad functional cooperation among the plasmids in shaping the phenotypic properties and symbiotic capabilities of rhizobia.Electronic supplementary materialThe online version of this article (doi:10.1007/s13353-014-0220-2) contains supplementary material, which is available to authorized users.
Highlights
Rhizobium leguminosarum bv. trifolii TA1 (RtTA1) is a soil bacterium establishing a highly specific symbiotic relationship with clover, which is based on the exchange of molecular signals between the host plant and the microsymbiont
Rhizobium leguminosarum bv. trifolii (Rlt) is a soil bacterium establishing a symbiotic relationship with clover, Trifolium spp. and inducing the formation of root nodules on the host plant, in which bacteria differentiate into nitrogen-fixing bacteroids
The interaction between rhizobia and leguminous plants shows a high degree of specificity, and successful infection of the roots is based on the exchange of molecular signals between the host plant and the microsymbiont (Dénarié et al 1996; Long 1996; Jones et al 2007)
Summary
Rhizobium leguminosarum bv. trifolii (Rlt) is a soil bacterium establishing a symbiotic relationship with clover, Trifolium spp. and inducing the formation of root nodules on the host plant, in which bacteria differentiate into nitrogen-fixing bacteroids. Trifolii (Rlt) is a soil bacterium establishing a symbiotic relationship with clover, Trifolium spp. and inducing the formation of root nodules on the host plant, in which bacteria differentiate into nitrogen-fixing bacteroids. The interaction between rhizobia and leguminous plants shows a high degree of specificity, and successful infection of the roots is based on the exchange of molecular signals between the host plant and the microsymbiont (Dénarié et al 1996; Long 1996; Jones et al 2007). The specificity of the interaction between symbiotic partners is mediated largely by the Nod factor (NF), a substituted lipochitooligosaccharide molecule synthesised by the action of rhizobial nodulation (nod) genes, usually located on one of the plasmids ( called a symbiotic plasmid, pSym) or on the chromosome as symbiotic islands (Long 1996; Masson-Boivin et al 2009).
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