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Evidence that the exoH gene of Sinorhizobium meliloti does not appear to influence symbiotic effectiveness with Medicago truncatula ‘Jemalong A17’

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The purpose of this study was to identify strains of Sinorhizobium meliloti that formed either an effective or completely ineffective symbiosis with Medicago truncatula L. ‘Jemalong A17’ and, subsequently, to determine whether differences existed between their exoH genes. Sinorhizobium meliloti TII7 and A5 formed an effective and ineffective symbiosis with M. truncatula ‘Jemalong A17’, respectively. Using a multilocus sequence typing method, both strains were shown to have chromosomes identical with S. meliloti Rm1021 and RCR2011. The 2260-bp segments of DNA stretching from the 3′ end of exoI through open reading frames of hypothetical proteins SM_b20952 and SM_b20953 through exoH into the 5′ end of exoK in strains TII7 and Rm1021 differed by a single nucleotide at base 127 of the hypothetical protein SM_b20953. However, the derived amino acid sequences of the exoH genes of effective TII7, ineffective A5, and strain Rm1021 were shown to be identical with each other. Therefore, it would seem unlikely that the gene product of exoH is directly involved with the low efficiency of a symbiosis of strain Rm1021 with M. truncatula ‘Jemalong A17’. Complementation or complete genome sequence analyses involving strains TII7 and A5 might be useful approaches to investigate the molecular bases for the differential symbiotic response with M. truncatula ‘Jemalong A17’.

Le but de cette étude était d’identifier les souches de Sinorhizobium meliloti qui formaient une symbiose efficace ou complètement inefficace avec Medicago truncatula Jemalong A17, et de déterminer subséquemment s’il existait des différences au niveau du gène exoH. Les souches de S. meliloti TII17 et A5 formaient respectivement des symbioses efficaces et inefficaces avec M. truncatula ‘Jemalong A17’. Les 2 souches possédaient des chromosomes identiques à ceux des souches Rm1021 et RCR2011 selon le typage de séquences multilocus. Les segments d’ADN de 2260 pb des souches TII17 et Rm1021 comprenant l’extrémité 3′ de exoI, le cadre de lecture ouvert des protéines hypothétiques SM_b20952 et SM_b20953, et exoH jusqu’à l’extrémité 5′ de exoK, ne différaient que par un seul nucléotide en position 127 de la protéine hypothétique SM_b20953. Cependant, les séquences déduites d’acides aminés du gène exoH de la souche efficace TII17 et des souches inefficaces A5 et Rm1021 étaient identiques. Ainsi, il semble peu vraisemblable que le produit du gène exoH soit directement impliqué dans la faible efficacité symbiotique de Rm1021 avec M. truncatula ‘Jemalong A17’. Des analyses de complémentation ou le séquençage du génome des souches TII17 et A5 pourraient être utiles pour examiner les bases moléculaires reliées à la réponse symbiotique différentielle avec M. truncatula ‘Jemalong A17’.

Document Type: Research Article

Publication date: December 1, 2010

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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