COMPARISON OF HOMOLOGOUS RECOMBINATION FREQUENCIES IN SOMATIC-CELLS OF PETUNIA AND TOBACCO SUGGEST 2 DISTINCT RECOMBINATION PATHWAYS

Homologous recombination in plants was studied using an extrachromosomal recombination assay in which intermolecular homologous recombination between two complementary plasmids restored a selectable marker gene. Several vectors containing an insertion into or deletions within the coding region of the neomycin phosphotransferase (NPT-II) gene were designed. Plasmids were introduced, in pairwise combinations, into protoplasts and homologous recombination events were measured by counting the number of NPT-II-resistant colonies. A 10-fold increase in recombination frequency was observed in Petunia hybrida RL01 compared to Nicotiana tabacum SRI. This difference occurred when one or both of the co-transferred recombination plasmids was offered in a circular form. Apart from such specific differences between two cultivars from different species, a two- to fivefold increase in recombination frequencies was observed when the genomic TBS (transformation booster sequence) fragment from P. hybrida was added onto one of the transferred plasmids. TBS-specific stimulation of recombination was observed in Petunia RL01. These data suggest that two different recombination pathways may be present in plants.