Insights into maize genome editing via CRISPR/Cas9

Abstract

Maize is an important crop for billions of people as food, feed, and industrial raw material. It is a prime driver of the global agricultural economy as well as the livelihoods of millions of farmers. Genetic interventions, such as breeding, hybridization and transgenesis have led to increased productivity of this crop in the last 100 years. The technique of genome editing is the latest advancement in genetics. Genome editing can be used for targeted deletions, additions, and corrections in the genome, all aimed at genetic enhancement of crops. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR associated protein 9 (CRISPR/Cas9) system is a recent genome editing technique that is considered simple, precise, robust and the most revolutionary. This review summarizes the current state of the art and predicts future directions in the use of the CRISPR/Cas9 tool in maize crop improvement.

Keywords: CRISPR; Cas9; Gene editing; Genome modification; Maize.

Fig. 1

Representative model depicting CRISPR/Cas9 system for genome modification. The Cas9 protein contains two catalytic nuclease domains: RuvC and HNH. It generates a double stranded break (DSB) at target sites with complementarity to single guide RNA (sgRNA) which can later be edited via Non homologous end—joining (NHEJ) or Homologous—directed repair (HDR)

Fig. 2

Representative model depicting the newly described alternative forms of the Cas9 protein. a Cas9 nickase created by mutation of either of RuvC or HNH nuclease domain; a1 Cas9 nickase created by mutation in the HNH domain cleaves non complementary DNA strand; a2 Cas9 nickase created by mutation in the RuvC nuclease domain, cleaves complementary DNA strand; a3 Paired nickase creates a displaced double stranded break. This strategy improves specificity. b The catalytically inactive or nuclease deficient or ‘dead’ Cas9 (dCas9) (that is mutations in both the RuvC and HNH domains) can specifically target genome based on sgRNA sequence, without cleaving DNA. The dCas9 can be fused to various effector domains such as transcriptional activator, repressor or GFP protein to perform other functions at the target site