DNA base editing in nuclear and organellar genomes

Genome editing continues to revolutionize biological research. Due to its simplicity and flexibility, CRISPR/Cas-based editing has become the preferred technology in most systems. Cas nucleases tolerate fusion to large protein domains, thus allowing combination of their DNA recognition properties with new enzymatic activities. Fusion to nucleoside deaminase or reverse transcrip-tase domains has produced base editors and prime editors that, instead of generating double-strand breaks in the target sequence, induce site-specific alterations of single (or a few adjacent) nucleotides. The availability of protein -only genome editing reagents based on transcription activator-like effectors has enabled the extension of base editing to the genomes of chloroplasts and mitochondria. In this review, we summarize currently available base editing methods for nuclear and organellar genomes. We highlight recent advances with improving precision, specificity, and efficiency and discuss current limita-tions and future challenges. We also provide a brief overview of applications in agricultural biotechnology and gene therapy.