1Laboratoire des Interactions Plantes Microorganismes. Centre National de la Recherche Scientifique (UMR 2594), Institut National de la Recherche Agronomique (UMR 441), BP27, 31326 Castanet, Tolosan cedex, France; 2Laboratoire des IMRCP, UMR5623 UPS/CNRS, 118 route de Narbonne, F-31062, Toulouse cedex, France
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Accepted 23 October 2003.
In this article, we describe the typA gene of Sinorhizobium meliloti, the orthologue of typA/bipA genes found in a wide range of bacteria. We found that typA was required for survival of S. meliloti under certain stress conditions, such as growth at low temperature or low pH and in the presence of sodium dodecyl sulfate (SDS). The cold-sensitive phenotype of both Escherichia coli bipA and S. meliloti typA mutants were cross-complemented, indicating that the two genes are functionally equivalent. typA was indispensable for symbiosis on Medicago truncatula Jemalong and F83005.5 and contributes to the full efficiency of symbiosis on other host plant lines such as DZA315.16 or several cultivars of M. sativa. Hence, the symbiotic requirement for typA is host dependent. Interestingly, the symbiotic defect was different on Jemalong and F83005.5 plants, thus indicating that typA is required at a different stage of the symbiotic interaction.
The American Phytopathological Society, 2004