Hairy-root-inducing plasmid: physical map and homology to tumor-inducing plasmids

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Abstract
A physical map was constructed for the 250-kilobase (kb) plasmid pRiA4b, which confers the virulence properties of a strain of Agrobacterium rhizogenes for hairy root disease in plants. The complete HindIII and KpnI restriction map was determined from a collection of overlapping HindIII partial digest clones. Homologous regions with 2 plasmids that confer virulence for crown gall disease, plasmids pTiA6 and pTiT37, were mapped on pRiA4b. As much as 160 kb of pRiA4b had detectable homology to 1 or both of these crown-gall-tumor-inducing plasmids. About 33 kb of pRiA4b hybridized to the vir region of pTiA6, a segment of DNA required for virulence of A. tumefaciens. Portions of pTiA6 and pTiT37 transferred into plant cells in crown gall disease (T-DNA), shared limited homology with scattered regions of pTiA4b. The tumor morphology loci tms-1 and tms-2 from the T-DNA of pTiA6 hybridized to pRiA4b. A T-DNA fragment containing the tml and tmr tumor morphology loci also hybridized to pRiA4b, but the homology was not defined to a locus and is probably not specific to tmr. A segment of pRiA4b T-DNA which was transferred into plant cells in hairy root disease lacked detectable homology to pTiA6 and had limited homology at one end to the T-DNA of pTiT37.