Efficient plastid transformation has been achieved in Nicotiana tabacum using cloned plastid DNA of
Solanum nigrum carrying mutations conferring spectinomycin and streptomycin resistance. The use of the
incompletely homologous (homeologous) Solanum plastid DNA as donor resulted in a Nicotiana plastid
transformation frequency comparable with that of other experiments where completely homologous plastid
DNA was introduced. Physical mapping and nucleotide sequence analysis of the targeted plastid DNA
region in the transformants demonstrated efficient site-specific integration of the 7.8-kb Solanum plastid
DNA and the exclusion of the vector DNA. The integration of the cloned Solanum plastid DNA into
the Nicotiana plastid genome involved multiple recombination events as revealed by the presence of
discontinuous tracts of Solanum-specific sequences that were interspersed between Nicotiana-specific
markers. Marked position effects resulted in very frequent cointegration of the nonselected peripheral
donor markers located adjacent to the vector DNA. Data presented here on the efficiency and features
of homeologous plastid DNA recombination are consistent with the existence of an active RecA-mediated,
but a diminished mismatch, recombination/repair system in higher-plant plastids
