The invention relates to methods and compositions for site-specific recombinase-mediated mobilization of viral replicons and associated DNAs of interest from T-DNA. The methods of the invention comprise Agrobacterium-mediated transfer of T-DNA to a plant cell, wherein the T-DNA contains a viral replicon flanked by directly repeated target sites for a site-specific recombinase and optionally a DNA of interest linked to the viral replicon. The DNA of interest may also contain a non-identical target site for the recombinase. An expression cassette for the site-specific recombinase is present on the T-DNA or the plant genome, or is transiently introduced into the plant cell. Expression of the site-specific recombinase in the plant cell results in excision of the viral replicon and the associated DNA of interest. The viral replicon and DNA of interest are then replicated to high copy number in the host plant cell.