Characteristics of Ti plasmids from broad-host-range and ecologically specific biotype 2 and 3 strains of Agrobacterium tumefaciens

Abstract

A. tumefaciens strains isolated from crown gall tumors on grapevines in California [USA] were consistently of the biotype 3 group. All 11 of these strains were limited in their host range and harbored Ti plasmids with molecular masses between 119 and 142 megadaltons (Mdal) as well as a larger cryptic plasmid of > 200 Mdal; occasionally a smaller cryptic plasmid of 65 Mdal was also present. Ti plasmids of these strains have DNA sequences in common with Ti plasmids of octopine and nopaline strains belonging to the biotype 1 group and exhibited sequence homologies with the conserved region of the T-DNA. Of the 11 strains, utilized octopine as a sole source of C and N and 3 strains catabolized both octopine and nopaline, whereas 1 strain catabolized only nopaline. All of these strains were resistant to the bacteriocin agrocin-84, except 1 grapevine strain that belonged to the biotype 1 group and was agrocin sensitive; it also differed in its plasmid and virulence characteristics. Isolations from Rubus ursinus ollalieberry galls yielded exclusively biotype 2 strains. These strains were insensitive to agrocin-84, utilized nopaline as a sole C and N source, and were highly virulent on all host plants tested. They contained Ti plasmids ranging between 100 and 130 Mdal and occasionally a cryptic plasmid of 69 Mdal. Their Ti plasmids have DNA sequences in common with Ti plasmids of biotype 1 strains and with the conserved region of the T-DNA.