Simple and efficient plastid transformation system for the liverwort Marchantia polymorpha L. suspension-culture cells

We have established a simple and efficient plastid transformation system for liverwort, Marchantia polymorpha L., suspension-culture cells, which are homogenous, chloroplast-rich and rapidly growing. Plasmid pCS31 was constructed to integrate an aadA expression cassette for spectinomycin-resistance into the trnI-trnA intergenic region of the liverwort plastid DNA by homologous recombination. Liverwort suspension-culture cells were bombarded with pCS31-coated gold projectiles and selected on a medium containing spectinomycin. Plastid transformants were reproducibly isolated from the obtained spectinomycin-resistant calli. Selection on a sucrose-free medium greatly improved the efficiency of selection of plastid transformants. Homoplasmic plastid transformant lines were established by successive subculturing for 14 weeks or longer on the spectinomycin-containing medium. The plastid transformation system of liverwort suspension-culture cells should facilitate the investigation of the fundamental genetic systems of plastid DNA, such as replication.