Herbicide-resistant plants produced by precision adenine base editing in plastid DNA

CRISPR-free, protein-only cytosine base editors (CBEs) or adenine base editors, composed of DNA-binding proteins such as zinc finger proteins or transcription activator-like effectors (TALEs) and nucleobase cytosine or adenine deaminases, respectively, enable organellar DNA editing in cultured cells, animals and plants^1-4. TALE-linked double-stranded DNA deaminase toxin A (DddA_tox)-derived CBEs (DdCBEs) and TALE-linked adenine deaminases (TALEDs) install C-to-T and A-to-G single-nucleotide conversions, respectively, in mitochondria and chloroplasts^5-9. Interestingly, whereas TALEDs exclusively induce A-to-G conversions without C-to-T conversions in mammalian mitochondrial DNA¹⁰, they often install unwanted C-to-T edits in addition to intended A-to-G edits in plastid DNA^7,9,11,12. Here we show that uracil DNA glycosylase (UDG)-fused TALEDs (UDG-TALEDs) minimize C-to-T conversions without reducing the A-to-G editing efficiency and install a mutation in the chloroplast psbA gene that encodes a single-amino-acid substitution (S264G), which confers herbicide resistance in the resulting plants.