CRISPR-Cas12a base editors confer efficient multiplexed genome editing in rice

Dear Editor,Many Cas9-derived base editors have been developed for precise C-to-T and A-to-G base editing in plants(Molla et al.,2021).They are typically based on a SpCas9 nickase or its engineered variants with altered protospacer adjacent motif(PAM)requirements(Molla et al.,2021).CRISPR-Cas12a enables highly efficient multiplexed genome editing in plants,and its T-rich PAM preference complements the G-rich PAM requirement of SpCas9 in genome targeting(Zhang et al.,2019,2021).Because of the lack of an efficient Cas12a nickase,it has been challenging to develop efficient Cas12a base editors.Nevertheless,Cas12a cytosine base editors(CBEs)and adenine base editors(ABEs)have been developed in mammalian cells(Li et al.,2018;Kleinstiver et al.,2019)with low DNA damage(Wang et al.,2020)because deactivated Cas12a(dCas12a)was used.However,efficient dCas12a base editors are yet to be developed in plants.

Hypercompact CRISPR–Cas12j2 (CasF) enables genome editing, gene activation, and epigenome editing in plants

CRISPR-Cas9,-Cas12a,-Cas12b,and-Cas13 have been harnessed for genome engineering in human and plant cells(Liu et al.,2022).However,the large size of these Cas proteins(e.g.190 kDa for SpCas9)makes them difficult to deliver into cells via a viral vector.The development of smaller Cas proteins will lead to reduced viral vector sizes that can be more widely adopted in versatile genome engineering systems.Recently,a CRISPR-Cas12j2(CasF)system was discovered in huge phages and developed into a hypercompact genome editor due to the small size of Cas12j2(80 kDa)(Pausch et al.,2020).Unfortunately,the gene editing efficiency of Cas12j2 in Arabidopsis protoplasts using ribonucleoprotein delivery was less than one percent(Pausch et al.,2020).Further optimization of this system is clearly required if CRISPR-Cas12j2-mediated editing in plant genomes is to be adopted by the plant sciences community.