Abstract: Site-specific C-to-U RNA editing is a hallmark of plant organelle transcript maturation. Up to thousands of specific cytidines are converted into uridines in plant chloroplasts and mitochondria, with no evidence of editing activity in the cytosol.

Specific nuclear-encoded pentatricopeptide repeat (PPR) proteins are the key factors of plant C-to-U RNA editing and tightly co-evolve with their organellar targets. As an example, PPR78 of the model moss Physcomitrium patens targets two mitochondrial RNA editing sites: cox1eU755SL and rps14eU137SL. The editing efficiencies at the rps14 site vary highly within mosses. We found that the variable editing rates are conferred by the different PPR78 orthologues. Moreover, we found that representatives of the Hypnales order, where both known edits of PPR78 are obsolete, still retain an ortholog. We considered the possibility that PPR78 may have an unrecognized extra function and identified ccmFNeU1465RC as an additional candidate editing site. Using our recently established E. coli RNA editing setup, we could confirm that PPR78 can indeed target the predicted “new” editing site ccmFNeU1465RC upon heterologous expression.

Just recently, we have transferred three plant mitochondrial PPR editing factors, PpPPR56, PpPPR65 and PpPPR78, into human cell lines. We found that they do not only faithfully edit their native, co-delivered targets but also perform C-to-U RNA editing on numerous endogenous off-targets in the human nucleo-cytosolic transcriptome, which are to a large extent explained by known PPR-RNA binding properties. We conclude that plant PPR editing factors are not per se incompatible with the eukaryotic nucleo-cytosol. Finally, engineering two crucial amino acid positions in the PPR array of PpPPR56 led to predictable shifts in target recognition and the resulting set of off-targets, paving the way for targeting PPR editing factors to non-native transcripts in future.

Biography:

• B.Sc. Biology in Bonn, Germany
• M.Sc. Plant Sciences in Bonn, Germany (thesis with Mareike Schallenberg-Rüdinger and Volker Knoop)
• Currently ongoing PhD studies in Volker Knoops lab, likely to finish beginning of next year