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Formation of Rhizobium phaseoli symbiotic plasmids by genetic recombination
G Soberón-Chávez1, R Nájera, G Espín
1Centro de Investigación sobre Ingeniería Genética y Biotecnología, UNAM, Cuernavacaca, Morelos, Mexico.
Abstract:
We report here the formation of symbiotic plasmids (pSyms), by genetic recombination between rearranged pSyms, which lack symbiotic information, and resistance plasmids carrying parts of different symbiotic plasmids (R's). This recombination was found to occur both between plasmids derived from different Rhizobium phaseoli isolates, and between plasmids derived from strains obtained from the same original isolate. We also present evidence on the formation of a functional symbiotic plasmid by recombination of an R', carrying nif and nod genes from strain CFN42, and an indigenous plasmid present in this strain (pCFN42e), which was thought to be unrelated to its symbiotic plasmid (pCFN42d). These data are discussed with respect to the stability and transfer of Rhizobium symbiotic information.
Insights
Genetic recombination between symbiotic plasmids (pSyms) and resistance plasmids (R's) can create new functional pSyms in Rhizobium phaseoli. This process impacts the stability and transfer of essential symbiotic genes.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Symbiotic plasmids (pSyms) are crucial for nitrogen fixation in Rhizobium bacteria.
- Understanding the mechanisms of pSym formation and maintenance is vital for agricultural applications.
- Previous studies have focused on pSym stability but less on their dynamic formation.
Purpose of the Study:
- To investigate the formation of symbiotic plasmids (pSyms) through genetic recombination.
- To explore the role of resistance plasmids (R's) in pSym formation.
- To analyze the implications of these recombination events for the stability and transfer of symbiotic information in Rhizobium.
Main Methods:
- Analysis of genetic recombination events between different plasmid types.
- Characterization of plasmid DNA from Rhizobium phaseoli isolates.
- Identification of genes (nif and nod) involved in symbiotic functions.
Main Results:
- Demonstrated pSym formation via recombination between rearranged pSyms and R's.
- Observed recombination between plasmids from different and same Rhizobium phaseoli isolates.
- Confirmed formation of a functional pSym by recombining an R' (carrying nif and nod genes) with an indigenous plasmid (pCFN42e).
Conclusions:
- Genetic recombination is a key mechanism for generating novel symbiotic plasmids.
- Resistance plasmids can contribute essential symbiotic genes, influencing pSym diversity.
- These findings provide insights into the plasticity and evolution of symbiotic genetic elements in Rhizobium.