De novo RNA base editing in plant organelles with engineered synthetic P-type PPR editing factors

In plant mitochondria and chloroplasts, cytidine-to-uridine RNA editing plays a crucial role in regulating gene expression. While natural PLS-type PPR proteins are specialized in this process, synthetic PPR proteins offer significant potential for targeted RNA editing. In this study, we engineered chimeric editing factors by fusing synthetic P-type PPR guides with the DYW cytidine deaminase domain of a moss mitochondrial editing factor, PPR56. These designer PPR editors (dPPRe) elicited efficient and precise de novo RNA editing in Escherichia coli, and in Nicotiana benthamiana chloroplasts and mitochondria. Chloroplast transcriptome-wide analysis of the most efficient dPPRe revealed minimal off-target effects, with only three non-target C sites edited due to sequence similarity with the intended target. This study introduces a novel and precise method for RNA base editing in plant organelles, paving the way for new approaches in gene regulation applicable to plants and potentially other organisms.