NONRECIPROCAL HOMOLOGOUS RECOMBINATION BETWEEN AGROBACTERIUM TRANSFERRED DNA AND A PLANT CHROMOSOMAL LOCUS

Previously, we demonstrated the occurrence of gene targeting in tobacc o cells after Agrobacterium-mediated transformation. In these experime nts a defective kanamycin resistance (Km(r)) gene residing at a chromo somal location was restored via homologous recombination with an incom ing transferred DNA (T-DNA) repair construct (pSDM101) containing a di fferent defective Km(r) gene. In this article we describe gene targeti ng experiments with the same target line, but using an improved repair construct, pSDM321. In one of the Km(r) calli obtained after transfor mation with pSDM321 (line A) the product of homologous recombination w as detected using PCR. Further molecular analysis revealed that the de fective Km(r) gene present on the incoming T-DNA had been restored via homologous recombination with the target locus. The target locus was left unchanged and the corrected T-DNA was found to be inserted on the same chromosome but not close to the target locus. This paper present s molecular evidence in plants for the conversion of an introduced DNA molecule (in this case, T-DNA) by a homologous chromosomal locus.