Chapter 46 - CRISPR-Cas system-a promising tool for engineering resistance to plant viruses

Abstract

Among the precise geneediting methods, clustered regularly interspaced short palindromic repeats–Cas9 (CRISPR-Cas9) is becoming a method of choice for the control of plant viruses, as compared with zinc finger nucleases and transcription activator–like effector endonucleases. The CRISPR-Cas system is an adaptive immune system of bacteria and archaea that guard against invasion by foreign nucleic acids including viruses. It has successfully been used to control both DNA and RNA plant viruses using short guide RNAs (20 nt) specific to virus genomes. In the case of DNA viruses, the genome of the virus, rather than the host genome, was targeted; for RNA viruses, in addition to the virus genome, the host susceptibility gene (e.g., eIF4E) was targeted to confer virus resistance. The advantage of targeting host genes is that transgenic constructs could be segregated out in later generations. However, when virus genome is targeted, as in case of DNA viruses, both Cas9 nuclease and guide RNA have to be constitutively expressed in the plant genome to act on the virus infection.