# TALE-based C-to-T base editor for multiple homologous genes with flexible precision

## TL;DR

This paper introduces a TALE-based C-to-T base editing method that allows precise editing of multiple similar genes in Arabidopsis while reducing off-target effects.

## Contribution

A novel TALE system with a flexible repeat unit enables simultaneous editing of homologous genes with high precision.

## Key findings

- The TALE-based system achieved efficient C-to-T editing in Arabidopsis nuclear genes.
- The method allows for variations in the third base of codons in homologous genes.
- Off-target substitutions were significantly suppressed using this strategy.

## Abstract

Recently a cytidine deaminase-based method for highly efficient C-to-T targeted base editing was developed and has been used with CRISPR-mediated systems. It is a powerful method for genome engineering, although it is prone to off-target effects and has a limited targeting scope. Transcription activator-like effector (TALE)-based tools which allow longer recognition sequences than do CRISPR/Cas9 systems, can also be used for targeted C-to-T base editing. Here, we describe a method that efficiently achieved targeted C-to-T substitutions in Arabidopsis nuclear genes using cytidine deaminase fused to a TALE DNA-binding domain. We used a single pair of TALEs with a novel TALE-repeat unit that can recognize all four DNA bases, especially to allow for variations in the third base of codons in homologous genes. This targeting strategy makes it possible to simultaneously base edit almost identical sites in multiple isoforms of a gene while suppressing off-target substitutions.