Dear Editor,Single-nucleotide polymorphism (SNP) is an abundant form of genetic variation among individuals in plant species,which has been believed to have effects on the gene function responsible for phenotypic diversity.Utilization of functional SNPs associated with diverse important agronomic traits is of great value in crop improvements.Recently,a simple base editing system,which introduces a single-nucleotide change in genes of interest for generating gain-of-function mutants,has been developed in plants (Li et al.,2017;Lu and Zhu,2017;Ren et al.,2017),in which Cas9(D10A) nickase is engineered with the rat cytosine deaminase (APOBEC1) and the uracil glycosylase inhibitor (UGI).Under the guidance of sgRNA,the Cas9n fusion protein is directed to the target locus in the genome,deaminating cytidines (C) in the editing window (13-19 bp before the PAM sequence) into uridines (U) and enabling the introduction of thymines (T),adenines (A) or guanines (G) during DNA replication (Li et al.,2017;Lu and Zhu,2017;Ren et al.,2017).