On- and Off-Target Analyses of CRISPR-Cas12b Genome Editing Systems in Rice.

The CRISPR-associated Cas12b system is the third most efficient CRISPR tool for targeted genome editing in plants after Cas9 and Cas12a. Although the genome editing ability of AaCas12b has been previously investigated in rice, its off-target effects in plants are largely not known. In this study, we first engineered single-guide RNA (sgRNA) complexes with various RNA scaffolds to enhance editing frequency. We targeted ( and ( genes with GTTG and ATTC protospacer adjacent motifs, respectively. The use of two scaffolds (Aac and Aa1.2) significantly increased the frequency of targeted mutagenesis. Next, we performed whole-genome sequencing (WGS) of stably transformed T rice plants to assess off-target mutations. WGS analysis revealed background mutations in both coding and noncoding regions with no evidence of sgRNA-dependent off-target activity in edited genomes. We also showed Mendelian segregation of insertion and deletion (indel) mutations in T generation. In conclusion, both Aac and Aa1.2 scaffolds provided precise and heritable genome editing in rice.