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Keywords:

  • salinity;
  • ACC deaminase;
  • mesorhizobia;
  • symbiosis;
  • stress tolerance

Abstract

Our goal was to study the symbiotic performance of two Mesorhizobium ciceri strains, transformed with an exogenous 1-aminocyclopropane-1-carboxylate deaminase gene (acdS), in chickpea plants under salinity stress. The EE-7 (salt-sensitive) and G-55 (salt-tolerant) M. ciceri strains were transformed with an acdS gene present on plasmid pRKACC. Salinity significantly reduced the overall growth of plants inoculated with either wild-type strains. Although the growth of plants inoculated with either salt-sensitive or salt-tolerant strain was reduced under salinity, the salt-tolerant strain showed a higher ability to nodulate chickpea under salt stress compared with the salt-sensitive strain. The shoot dry weight was significantly higher in plants inoculated with the acdS-transformed salt-sensitive strain compared with the plants inoculated with the native strain in the presence of salt. The negative effects of salt stress were also reduced in nodulation when using acdS-transformed strains in comparison with the wild-type strains. Interestingly, by expressing the exogenous acdS gene, the salt-sensitive strain was able to induce nodules in the same extent as the salt-tolerant strain. Although preliminary, these results suggest that genetic modification of a Mesorhizobium strain can improve its symbiotic performance under salt stress and indicate that ACC deaminase can play an important role in facilitating plant–rhizobium interaction under salinity conditions.