Rhizobial Plasmids That Cause Impaired Symbiotic Nitrogen Fixation and Enhanced Host Invasion

• DOI: 10.1094/mpmi-02-12-0052-r
• Publication Date: 2012-07-02T20:40:10Z
• Authors: Matthew B. Crook; Daniel P. Lindsay; Matthew B. Biggs; Joshua S. Bentley; Jared C. Price; Spencer C. Clement; Mark J. Clement; Sharon R. Long; Joel S. Griffitts
• Keywords: Sinorhizobium

The genetic rules that dictate legume-rhizobium compatibility have been investigated for decades, but the causes of incompatibility occurring at late stages nodulation process are not well understood. An evaluation naturally diverse legume (genus Medicago) and rhizobium Sinorhizobium) isolates has revealed numerous instances in which Sinorhizobium strains induce occupy nodules only minimally beneficial to certain Medicago hosts. Using these ineffective strain-host pairs, we identified gain-of-compatibility (GOC) rhizobial variants. We show GOC variants arise by loss specific large accessory plasmids, call HR plasmids due their effect on symbiotic host range. Transfer a symbiotically effective strain can convert it incompatibility, indicating act autonomously backgrounds. provide evidence may encode machinery horizontal transfer. On hosts impair N fixation, also enhance competitiveness nodule occupancy, showing occurring, transferrable genes rhizobia more exploitative lifestyle. This observation raises important questions about agricultural management, ecological stability mutualisms, factors distinguish symbionts from parasites.