Plant mitochondrial RNA editing

RNA editing affects messenger RNAs and transfer RNAs in plant mitochondria by site-specific exchange of cytidine and uridine bases in both seed and no nseed plants. Distribution of the phenomenon among bryophytes has been uncl ear since RNA editing has been detected in some but not all liverworts and mosses. A more detailed understanding of RNA editing in plants required ext ended data sets for taxa and sequences investigated. Toward this aim an int ernal region of the mitochondrial nad5 gene (1104 nt) was analyzed in a lar ge collection of bryophytes and green algae (Charales). The genomic nad5 se quences predict editing in 30 mosses, 2 hornworts, and 7 simple thalloid an d leafy liverworts (Jungermanniidae). No editing is, however, required in s even species of the complex thalloid liverworts (Marchantiidae) and the alg ae. RNA editing among the Jungermanniidae, on the other hand, reaches frequ encies of up to 6% of codons being modified. Predictability of RNA editing from the genomic sequences was confirmed by cDNA analysis in the mosses Sch istostega pennata and Rhodobryum roseum, the hornworts Anthoceros husnotii and A. punctatus, and the liverworts Metzgeria conjugata and Moerckia floto viana. All C-to-U nucleotide exchanges predicted to reestablish conserved c odons were confirmed. Editing in the hornworts includes the removal of geno mic stop codons by frequent reverse U-to-C edits. Expectedly, no RNA editin g events were identified by cDNA analysis in the marchantiid liverworts Ric ciocarpos natans, Corsinia coriandra, and Lunularia cruciata. The findings are discussed in relation to models on the phylogeny of land plants.