The length of the sgRNA-DNA complementary sequence is a key factor influencing the cleavage activity of Streptococcus pyogenes Cas9 (SpCas9) and its variants.The detailed mechanism remains unknown.Here,based on in vitro cleavage assays and base editing analysis,we demonstrate that reducing the length of this complementary region can confer nickase activity on SpCas9 and eSpCas9(1.1).We also show that these nicks are made on the target DNA strand.These properties encouraged us to develop a dual-functional system that simultaneously carries out double-strand DNA cleavage and C-to-T base conversions at separate targets.This system provides a novel tool for achieving trait stacking in plants.