Development of cytosine and adenine base editors for maize precision breeding

Base editing technologies can improve crops, but their efficiency in maize remains suboptimal. This study attempts to overcome these limitations by examining optimized cytosine and adenine base editors (CBEs and ABEs), namely evoAPOBEC1, evoFERNY, evoCDA1, TadA8.20, and TadA8e, for precise genome editing in transient and stable expression maize cells. Employing a seed fluorescence reporter (SFR) system for rapid screening of BE transformants and transgene-free progenies, we enhanced editing efficiencies and heritability. Notably, TadA8.20 and evoCDA1 attained multiplexed editing efficiencies of up to 100.0% and 79.0% at the tested loci, respectively, with some homozygous and bi-allelic mutants exceeding 72.4% and 73.7%. Precise editing of ZmACC1/2 (acetyl-CoA carboxylase) improved herbicide resistance, with ZmACC2 mutants displaying improved performance. This study advances crop genetic engineering by facilitating robust, multi-locus modifications without altered agronomic performance, enhancing herbicide tolerance in maize. The successful utilization of these BE is a significant step forward in agricultural biotechnology and precision breeding.