One C-to-U RNA Editing Site and Two Independently Evolved Editing Factors: Testing Reciprocal Complementation with DYW-Type PPR Proteins from the MossPhyscomitrium(Physcomitrella)patensand the Flowering PlantsMacadamia integrifoliaand Arabidopsis

Cytidine-to-uridine RNA editing is a posttranscriptional process in plant organelles, mediated by specific pentatricopeptide repeat (PPR) proteins. In angiosperms, hundreds of sites undergo RNA editing. By contrast, only 13 sites are edited in the mossPhyscomitrium(Physcomitrella)patens. Some are conserved between the two species, like the mitochondrial editing site nad5eU598RC. The PPR proteins assigned to this editing site are known in both species: the DYW-type PPR protein PPR79 inP. patensand the E+-type PPR protein CWM1 in Arabidopsis (Arabidopsis thaliana). CWM1 also edits sites ccmCeU463RC, ccmBeU428SL, and nad5eU609VV. Here, we reciprocally expressed theP. patensand Arabidopsis editing factors in the respective other genetic environment. Surprisingly, theP. patensediting factor edited all target sites when expressed in the Arabidopsiscwm1mutant background, even when carboxy-terminally truncated. Conversely, neither Arabidopsis CWM1 nor CWM1-PPR79 chimeras restored editing inP. patens ppr79 knockoutplants. A CWM1-like PPR protein from the early diverging angiosperm macadamia (Macadamia integrifolia) features a complete DYW domain and fully rescued editing of nad5eU598RC when expressed inP. patens.We conclude that (1) the independently evolvedP. patensediting factor PPR79 faithfully operates in the more complex Arabidopsis editing system, (2) truncated PPR79 recruits catalytic DYW domains in trans when expressed in Arabidopsis, and (3) the macadamia CWM1-like protein retains the capacity to work in the less complexP. patensediting environment. DYW-type PPR proteins independently evolved in mosses and flowering plants restore RNA editing defects across wide phylogenetic distances.