An Arabidopsis histone H2A mutant is deficient in Agrobacterium T-DNA integration

Agrobacterium tumefaciens genetically transforms plant cells by transferrin g a portion of the bacterial Ti-plasmid, the T-DNA, to the plant and integr ating the T-DNA into the plant genome. Little is known about the T-DNA inte gration process, and no plant genes involved in integration have yet been i dentified. We characterized an Arabidopsis mutant generated by T-DNA insert ional mutagenesis, rat5, that is resistant to Agrobacterium root transforma tion. rat5 contains two copies of T-DNA integrated as a tandem direct repea t into the 3' untranslated region of a histone H2A gene, upstream of the po lyadenylation signal sequence. Transient and stable beta-glucuronidase expr ession data and assessment of the amount of T-DNA integrated into the genom es of wild-type and rat5 Arabidopsis plants indicated that the rat5 mutant is deficient in T-DNA integration. We complemented the rat5 mutation by exp ressing the RAT5 histone H2A gene in the mutant plant. Overexpression of RA T5 in wild-type plants increased Agrobacterium transformation efficiency, F urthermore, transient expression of a RAT5 gene from the incoming T-DNA was sufficient to complement the rat5 mutant and to increase the transformatio n efficiency of wild-type Arabidopsis plants.