Structures of C-to-U RNA editing enzymes in plant organelles suggest different regulation mechanisms / Plastid and mitochondrial genome editing in plants

Abstract Mizuki Takenaka

The genetic information encoded in land plant mitochondrial and chloroplast genomes contains many "mistakes". These "mistakes" are accurately corrected by C-to-U RNA editing. Many pentatricopeptide repeat (PPR) proteins that bind to RNA in a sequence-specific manner have been identified as RNA editing factors. The editing enzyme DYW domain, which converts cytidine (C) to uridine (U) is present at the C-terminus of PPR proteins or works by forming a complex with other PPR proteins. We reported the first structures of the DYW domain from the chloroplast RNA editing factor OTP86, suggesting that cytidine deaminase activity of the DYW domain located at the C-terminus is regulated by conformational changes of the internal gating domain [1]. We also determined the structure of the DYW domain in DYW1, which forms a complex with a PPR protein CRR4 in chloroplasts [2]. The DYW domain of DYW1 shows a different gating domain structure from that in OTP86 and lacks a conserved N-terminal PG-box. Here we discuss the two different regulation mechanisms of C-to-U RNA editing enzymes in plant organelles.

[1] Takenaka et al. (2021) Nature Catalysis 4, 510-522

[2] Toma-Fukai et al. (2022) Plant Cell, DOI: 10.1093/plcell/koac318

Abstract Shin-ichi Arimura

Plastid and mitochondrial genomes (Organellar genomes) have been highly-demanded targets to be modified. Recently, we and other groups have developed genome editing technologies using TALENs or their related base editors with organellar targeting signals expressed from the nucleus for inheritable stable modifications of the organellar genomes. The organellar genome has high copy numbers, but the probable high expression and activity of the genome-editing enzymes enabled us to have the homoplasmic genome-edited plants even in the first generation of the transformants. I will introduce these genome editing techniques for these two organelle genomes and will discuss some use for molecular analyses to uncover biological subjects.

[1] Kazama T, Okuno M, Watari Y, Yanase S, Koizuka C, Tsuruta Y, Sugaya H, Toyoda A, Itoh T, Tsutsumi N, Toriyama K, Koizuka N, Arimura SI Curing cytoplasmic male sterility via TALEN-mediated mitochondrial genome editing. Nature plants 5 (7) 722-730 2019

[2] Issei Nakazato, Miki Okuno, Hiroshi Yamamoto, Yoshiko Tamura, Takehiko Itoh, Toshiharu Shikanai, Hideki Takanashi, Nobuhiro Tsutsumi and Shin-ichi Arimura, Nature Plants, 7, 906-913 (2021)