NEW AGROBACTERIUM HELPER PLASMIDS FOR GENE-TRANSFER TO PLANTS

We describe the construction of new helper Ti plasmids for Agrobacteri um-mediated plant transformation. These plasmids are derived from thre e different Agrobacterium tumefaciens Ti plasmids, the octopine plasmi d pTiB6, the nopaline plasmid pTiC58, and the L,L-succinamopine plasmi d pTiBo542. The T-DNA regions of these plasmids were deleted using sit e-directed mutagenesis to yield replicons carrying the vir genes that will complement binary vectors in trans. Data are included that demons trate strain utility. The advantages of Agrobacterium strains harbouri ng these 'disarmed' Ti plasmids for plant transformation via Agrobacte rium are discussed.