CRISPR/Cas technology for plant genome editing.

Abstract

CRISPR/Cas acts as a type of adaptive immunity in prokaryotes. It can degrade exogenous genes from an invading phage or plasmid and was first observed in1987. Ishino et al. (1987) found an interval approximately 32 nt of non-repetitive sequences and “tandem repeats” down-stream from the iap gene in Escherichia coli.In 2002,the “tandem repeats” were called “clustered regularly interspaced short palindromic repeats” (CRISPR). In 2005, the CRISPR spacer sequence was found to be highly homologous with exogenous sequences from bacterial plasmids and phages. As a result of this homology between host and exogenous substances, CRISPR is able to cleave foreign DNA and this system was developed in 2013. CRISPR/Cas only requires a short guide RNA sequence to recognize the target loci, the endonuclease activity of Cas can lead to gene modification by cleaving the target DNA and forming DNA double-strand breaks (DSBs) that stimulate DNA repair mechanisms in vivo, resulting in gene mutation (e.g., insertion, deletion and replacement). Compared with previously developed gene editing tools zinc finger nucleases (ZFNs), and transcription activator like effector nucleases (TALENs), CRISPR/Cas is more efficient and it can edit multiple target genes simultaneously. Based on these advantages, applications of CRISPR/Cas are rapidly developing. The ZFN and TALEN gene editing tools search valid sequences with proteins, while CRISPR/Cas depends on guide RNA (gRNA). Recently, a new genome editing technology was developed called NgAgo, which is applicable for editing genes in human cells with the DNA-mediated NgAgo endonuclease.