Requirement of Various Protein Combinations for Each C-to-U RNA Editosome in Plant Organelles

Abstract

In flowering plants, RNA editing converts several hundreds of organelle cytidines to uridines. Targeted cytidines are recognized by PLS class pentatricopeptide repeat (PPR) proteins, which bind RNA sequences upstream of the C targets in a sequence-specific manner. In the past several years, different types of proteins have been identified as RNA editing factors, including multiple organellar RNA editing factors/RNA editing factor interacting proteins (MORFs/RIPs), organelle RNA recognition motif (ORRM) proteins, organelle zinc finger (OZ) proteins, a P class PPR protein NUWA, short DYW proteins, and protoporphyrinogen oxidase 1 (PPO1). These proteins seem to contribute to individual RNA editing complexes in a different manner. Despite many key players for the assembly of editosomes having been revealed, the complete mechanism of the editing machinery including the deaminase enzymatic activity is still unclear. Plant editosomes are highly diverse not only due to the PLS class PPR proteins they contain but also in other components that are present. In this review, we introduce the recent progress in the field and discuss possible functions of each component in RNA editosomes in plant mitochondria and chloroplasts.