Alleviating the inhibitory effect of salinity stress on nod gene expression in Rhizobium tibeticum – fenugreek (Trigonella foenum graecum) symbiosis by isoflavonoids treatment

Abstract

Rhizobia-legume symbiosis depends on molecular dialog, which involves the production of specific plant flavonoid compounds as signal molecules. Rhizobium tibeticum was recovered from the root nodule of fenugreek and identified by sequencing the 16S rRNA gene. The effect of salinity stress on nod gene expression was measured in terms of β-galactosidase activity. R. tibeticum containing Escherichia coli lacZ gene fusions to specific nodulation (nod) genes were used to determine β-galactosidase activity. Combination of hesperetin (7.5 µM) and apigenin (7.5 µM) significantly increased β-galactosidase activity more than the single application of hesperetin or apigenin. Preincubation of R. tibeticum with hesperetin and apigenin combination significantly alleviates the adverse effect of salinity on nod gene expression and therefore, enhances nodulation and nitrogen fixation of fenugreek.

Keywords:

• Rhizobium tibeticum
• isoflavonoids
• salinity
• β-galactosidase
• nodulation

Acknowledgments

We are grateful to Professor Anna Skorupska and Dominika Maj for kindly providing E. coli α which contained the expression vector pMP221. This research was financially supported by the Science and Technology Development Fund (STDF), Ministry of Higher Education and Scientific Research, Egypt, project Grant no. 12 awarded to Professor Dr Mohamed Hemida Abd-Alla. The authors are grateful to the precious comments and careful correction made by anonymous reviewers for further improvements of this manuscript.