[Specificity and inheritance of rBE3 and rBE4 endonuclease-induced gene modifications in rice]

To gain more insights into the rice base editor (rBE3 and rBE4), we evaluated the mutation efficiency, off-target and inheritance of OsSERK1(D428N) and pi-ta(S918F) genes modified with rBE endonucleases. We predicted and analyzed the putative off-target sites of the sgRNA designed for OsSERK1(D428N) and pi-ta(S918F) by PCR amplification and Sanger sequencing. Then we further characterized the inheritance and stability of targeted base mutations and T-DNA segregation in the progeny of the self-fertilized T0 plants. Analysis of the DNA sequencing data of T0 plants of OsSERK1(D428N) revealed no nucleotide change at any of the four potential off-target sites. For OsSERK1(D428N) and Os08g07774 carry the same sgRNA targeting sites, base substitution at both two loci were detected at a frequency of 41.67%. The targeted base mutations could be transmitted readily to T1 progeny. Furthermore, genetic segregation caused the loss of T-DNA at a frequency between 25.0% and 40.9% in the T1 transgenic plants of OsSERK1(D428N) and pi-ta(S918F). These results demonstrated that the rBE3 and rBE4 systems could mediate specifically targeted base editing in one- or multi-site, and the targeted base editing could be stably inherited to next generation.