Simplified adenine base editors improve adenine base editing efficiency in rice

Summary Adenine base editors ( ABE s) have been exploited to introduce targeted adenine (A) to guanine (G) base conversions in various plant genomes, including rice, wheat and Arabidopsis . However, the ABE s reported thus far are all quite inefficient at many target sites in rice, which hampers their applications in plant genome engineering and crop breeding. Here, we show that unlike in the mammalian system, a simplified base editor ABE ‐P1S (Adenine Base Editor‐Plant version 1 Simplified) containing the ecTadA*7.10‐ nSpC as9 (D10A) fusion has much higher editing efficiency in rice compared to the widely used ABE ‐P1 consisting of the ecTadA‐ecTadA*7.10‐ nSpC as9 (D10A) fusion. We found that the protein expression level of ABE ‐P1S is higher than that of ABE ‐P1 in rice calli and protoplasts, which may explain the higher editing efficiency of ABE ‐P1S in different rice varieties. Moreover, we demonstrate that the ecTadA*7.10‐ nC as9 fusion can be used to improve the editing efficiency of other ABE s containing SaCas9 or the engineered Sa KKH ‐Cas9 variant. These more efficient ABE s will help advance trait improvements in rice and other crops.