Many studies reported the usefulness of the CRISPR gene editing technology using Cas9 and Cas12a (Cpf1) nucleases in humans and crops. These two nucleases differ by their recognition site, RNA requirement, and multiplexing ability, that is, Cas12a has a different protospacer adjacent motif (PAM) recognition site "NGG" requires only the CRISPR RNA (crRNA), and allows multiplexing. By contrast, Cas9 recognizes the "TTTV" PAM site, requires both crRNA and trans-activating RNA (tracrRNA), and does not allow multiplexing. These differences made the two nucleases deemed complementary to each other by scientists.

Scientist Kan Wang from Crop Bioengineering Center and Department of Agronomy at Iowa State University and colleagues see the lack of direct comparison between the two nucleases in one experiment. Thus, they compared the activities and specificities of the two enzymes in maize by targeting the glossy2 gene, which has sequences that can be recognized by both nucleases. Results showed that Cas9 had better performance in editing the gene compared with Cas12a, that is, Cas9 had 90 to100 percent edits, whereas Cas12a had 0 to 60 percent successful targets. However, they said that optimization is still needed to further test the activity of Cas12a in their experiments.

Read the full article in Plant Biotechnology Journal.