Characterization of Rhizobium phaseoli Sym plasmid regions involved in nodule morphogenesis and host-range specificity |
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| Authors: | M A Cevallos M Vázquez A Dávalos G Espín J Sepúlveda C Quinto |
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| Institution: | Departamento de Biología Molecular de Plantas, Centro de Investigacíon sobre Fijación de Nitrógeno, Morelos, México. |
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| Abstract: | Two nodulation regions from the symbiotic plasmid (pSym) of Rhizobium phaseoli CE-3 were identified. The two regions were contained in overlapping cosmids pSM927 and pSM991. These cosmids, in a R. phaseoli pSym-cured strain background, induced ineffective nodules on Phaseolus vulgaris roots. Transconjugants of Rhizobium meliloti harbouring pSM991 induced nodule-like structures on bean roots, suggesting that this cosmid contains host-range determinants. Analysis of deletions and insertional mutations in the sequences of pSM991 indicated that the genes responsible for the induction and development of nodules in P. vulgaris are organized in two regions 20 kb apart. One region, located in a 6.8 kb EcoRI fragment, includes the common nodABC genes. The other region, located in a 3.5 kb EcoRI fragment, contains information required for host-range determination. |
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