XVI International Botanical Congess

RNA editing by pyrimidine exchanges affects some 1000 nucleotide positions in plant mitochondrial mRNAs. RNA editing had been identified in all vascular plants but appears to be entirely absent from the thalloid liverwort Marchantia polymorpha. We have selected the mitochondrial nad5 and nad2 genes for analysis in bryophytes. RNA editing alters mRNAs in all groups of mosses but shows a striking divergence among the liverworts. Like in Marchantia no RNA editing is identified in other complex thalloid species but occurs with considerably varying frequency in the leafy liverworts (Jungermanniidae). A particularly high frequency of RNA editing is observed in the hornwort genus Anthoceros . A 1:1 ratio of U to C (`reverse´) vs. C to U exchanges in Anthoceros questions the historical designation of `reverse´ editing based on the 1:500 ratio in angiosperms.