Research progress of genome editing and derivative technologies in plants

Genome editing technologies using engineered nucleases have been widely used in many model organisms. Genome editing with sequence-specific nuclease (SSN) creates DNA double-strand breaks (DSBs) in the genomic target sites that are primarily repaired by the non-homologous end joining (NHEJ) or homologous recombination (HR) pathways, which can be employed to achieve targeted genome modifications such as gene mutations, insertions, replacements or chromosome rearrangements. There are three major SSNs─zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN) and clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR/Cas9) system. In contrast to ZFN and TALEN, which require substantial protein engineering to each DNA target, the CRISPR/Cas9 system requires only a change in the guide RNA. For this reason, the CRISPR/Cas9 system is a simple, inexpensive and versatile tool for genome engineering. Furthermore, a modified version of the CRISPR/Cas9 system has been developed to recruit heterologous domains that can regulate endogenous gene expression, such as activation, depression and epigenetic regulation. In this review, we summarize the development and applications of genome editing technologies for basic research and biotechnology, as well as highlight challenges and future directions, with particular emphasis on plants.