To construct a Cas9 expression cassette for the binary vector,the rice codon-optimized SpCas9 gene (21) was placed downstream of the maize ubiquitin 1 promoter (14) and
upstream of the nopaline synthase (NOS) gene terminator by BamHI and SpeI restriction and DNA ligation. The Cas9 cassette and a Gateway recombination cassette that
contained the attR1-ccdB-attR2 were cloned into pCAMBIA1300,which confers hygromycin B resistance (hptII) in transgenic plant (CAMBIA Health Solutions, Inc.), resulting
in a destination vector, pUbi-Cas9. Constructs derived from pUbi-Cas9 were used for rice transgenics. For transient expression of Cas9 in rice mesophyll protoplasts, the
pUC19 version of Cas9 was described earlier (21).