Identification of T-DNA tagged Arabidopsis mutants that are resistant to transformation by Agrobacterium

We have identified T-DNA tagged Arabidopsis mutants that are resistant to t ransformation by Agrobacterium tumefaciens (rat mutants). These mutants are highly recalcitrant to the induction of both crown gall tumors and phosphi nothricin-resistant calli, The results of transient GUS (beta-glucuronidase ) assays suggest that some of these mutants are blocked at an early step in the Agrobacterium-mediated transformation process, whereas others are bloc ked at a step subsequent to translocation of T-DNA into the nucleus. Attach ment of Agrobacterium to roots of the mutants rat1 and rat3 was decreased u nder various incubation conditions. In most mutants, the transformation-def icient phenotype co-segregated with the kanamycin resistance encoded by the mutagenizing T-DNA. In crosses with susceptible wild-type plants, the resi stance phenotype of many of these mutants segregated either as a semi-domin ant or dominant trait.