Pentatricopeptide repeat proteins: II. Present status and future prospects of PPR-based programmable RNA editing in crop improvement

Abstract

ABSTRACT RNA editing plays a major role in modulating gene expression. In higher plants, RNA editing has been observed in nuclear, chloroplast, and mitochondrial transcripts. In a companion paper, we have discussed the involvement of pentatricopeptide repeat (PPR) proteins in RNA editing in plants. In this review, we focus on the development of PPR protein-based programmable RNA editing (PRE) technology and its application to crop improvement. Site-directed RNA editing (SDRE) involves recruitment of RNA-editing enzymes to specific sites at selected transcripts. Limitations of SDRE have shifted the focus of researchers toward the PRE, wherein the RNA-binding platforms are engineered for the recognition of specific target sites. PRE tools include dead CRISPR/Cas-based or PPR protein-based platforms. REPAIR, CIRTS, RESCUE, RESTORE, and LEAPER are the five platforms based on the CRISPR-Cas system. Multiple organellar RNA-editing factors work well in association with the PPR proteins for an efficient and precise RNA editing at the target sites by forming an editosome. In this review, we highlight the PRE approaches that have potential to rectify defects attributable to single-base changes in plants through precise RNA-transcript editing, with no off-target effects in the genome, which will ultimately have a positive impact on crop improvement.