Dataset Information

Identification of an Exopolysaccharide Biosynthesis Gene in Bradyrhizobium diazoefficiens USDA110.

ABSTRACT: Exopolysaccharides (EPS) play critical roles in rhizobium-plant interactions. However, the EPS biosynthesis pathway in Bradyrhizobium diazoefficiens USDA110 remains elusive. Here we used transposon (Tn) mutagenesis with the aim to identify genetic elements required for EPS biosynthesis in B. diazoefficiens USDA110. Phenotypic screening of Tn5 insertion mutants grown on agar plates led to the identification of a mutant with a transposon insertion site in the blr2358 gene. This gene is predicted to encode a phosphor-glycosyltransferase that transfers a phosphosugar onto a polyprenol phosphate substrate. The disruption of the blr2358 gene resulted in defective EPS synthesis. Accordingly, the blr2358 mutant showed a reduced capacity to induce nodules and stimulate the growth of soybean plants. Glycosyltransferase genes related to blr2358 were found to be well conserved and widely distributed among strains of the Bradyrhizobium genus. In conclusion, our study resulted in identification of a gene involved in EPS biosynthesis and highlights the importance of EPS in the symbiotic interaction between USDA110 and soybeans.

SUBMITTER: Xu C

PROVIDER: S-EPMC8707904 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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Identification of an Exopolysaccharide Biosynthesis Gene in Bradyrhizobium diazoefficiens USDA110.

Xu Chunxia C Ruan Huaqin H Cai Wenjie W Staehelin Christian C Dai Weijun W

Microorganisms 20211201 12

Exopolysaccharides (EPS) play critical roles in rhizobium-plant interactions. However, the EPS biosynthesis pathway in Bradyrhizobium diazoefficiens USDA110 remains elusive. Here we used transposon (Tn) mutagenesis with the aim to identify genetic elements required for EPS biosynthesis in B. diazoefficiens USDA110. Phenotypic screening of Tn5 insertion mutants grown on agar plates led to the identification of a mutant with a transposon insertion site in the blr2358 gene. Thi ...[more]

PMID: 34946092

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Project description:Legume plants can form root organs called nodules where they house intracellular symbiotic rhizobium bacteria. Within nodule cells, rhizobia differentiate into bacteroids, which fix nitrogen for the benefit of the plant. Depending on the combination of host plants and rhizobial strains, the output of rhizobium-legume interactions varies from nonfixing associations to symbioses that are highly beneficial for the plant. Bradyrhizobium diazoefficiens USDA110 was isolated as a soybean symbiont, but it can also establish a functional symbiotic interaction with Aeschynomene afraspera In contrast to soybean, A. afraspera triggers terminal bacteroid differentiation, a process involving bacterial cell elongation, polyploidy, and increased membrane permeability, leading to a loss of bacterial viability while plants increase their symbiotic benefit. A combination of plant metabolomics, bacterial proteomics, and transcriptomics along with cytological analyses were used to study the physiology of USDA110 bacteroids in these two host plants. We show that USDA110 establishes a poorly efficient symbiosis with A. afraspera despite the full activation of the bacterial symbiotic program. We found molecular signatures of high levels of stress in A. afraspera bacteroids, whereas those of terminal bacteroid differentiation were only partially activated. Finally, we show that in A. afraspera, USDA110 bacteroids undergo atypical terminal differentiation hallmarked by the disconnection of the canonical features of this process. This study pinpoints how a rhizobium strain can adapt its physiology to a new host and cope with terminal differentiation when it did not coevolve with such a host.IMPORTANCE Legume-rhizobium symbiosis is a major ecological process in the nitrogen cycle, responsible for the main input of fixed nitrogen into the biosphere. The efficiency of this symbiosis relies on the coevolution of the partners. Some, but not all, legume plants optimize their return on investment in the symbiosis by imposing on their microsymbionts a terminal differentiation program that increases their symbiotic efficiency but imposes a high level of stress and drastically reduces their viability. We combined multi-omics with physiological analyses to show that the symbiotic couple formed by Bradyrhizobium diazoefficiens USDA110 and Aeschynomene afraspera, in which the host and symbiont did not evolve together, is functional but displays a low symbiotic efficiency associated with a disconnection of terminal bacteroid differentiation features.

Dataset Information

Identification of an Exopolysaccharide Biosynthesis Gene in Bradyrhizobium diazoefficiens USDA110.

Publications

Identification of an Exopolysaccharide Biosynthesis Gene in <i>Bradyrhizobium diazoefficiens</i> USDA110.

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