Incompatibility Behavior of a Non-symbiotic Plasmid pMhHN3015a in Mesorhizobium huakuii HN3015

Abstract:

The Tn5-mob-sacB-labeled non-symbiotic pMhHN3015a of Mesorhizobium huakuii HN3015 was respectively transferred into M. huakuii HN308SR and 7653R-1SR by tri-parent mating. Two transconju-gants, HN308SRN29 and 7653R-1SRN29 were obtained. The plasmid profiles of HN308SRN29 showed that pMhHN308b of HN308SR were cured. The results implied that pMhHN3015a and pMhHN308b were incompatible. However, the results from plasmid curing tests of HN308SRN29 showed that labeled plasmid cured derivative of HN308SRN29 could not be obtained. Since the sizes of pMhHN3015a and pMhHN308a were almost the same and their positions in agarose gels were difficult to distinguished, so that two plasmids might have been recombined and transposon Tn5 transferred into the chromosome. The plasmid profiles of transconjugant 7653R-1SRN29 showed that pMhHN3015a could coexist with pMh7653Ra. Furthermore, the results from plasmid curing tests of 7653R-1SRN29 showed that two mutants, 7653R-1SRN29D-A and 7653R-1SRN29D-B were obtained. The plasmid profiles showed that 7653R-1SRN29D-A and 7653R-1SRN29D-B lost pMhHN3015a, and that 7653R-1SRN29D-B showed an additional plasmid that was named p76H4. Results from plant nodulation tests showed that HN308SRN29 lost nodulation ability. But nodulation of 7653R-1SRN29 was enhanced. 7653R-1SRN29D-A could only form null nodules. How-ever, 7653R-1SRN29D-B lost its nodulation ability.