Targeted genome modifications in cereal crops

Abstract

The recent advent of customizable endonucleases has led to remarkable advances in genetic engineering, as these molecular scissors allow for the targeted introduction of mutations or even precisely predefined genetic modifications into virtually any genomic target site of choice. Thanks to its unprecedented precision, efficiency, and functional versatility, this technology, commonly referred to as genome editing, has become an effective force not only in basic research devoted to the elucidation of gene function, but also for knowledge-based improvement of crop traits. Among the different platforms currently available for site-directed genome modifications, RNA-guided clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) endonucleases have proven to be the most powerful. This review provides an application-oriented overview of the development of customizable endonucleases, current approaches to cereal crop breeding, and future opportunities in this field.

Keywords: CRISPR; TALEN; barley; maize; rice; wheat; zinc-finger nucleases.

Fig. 1.

Diagram summarizing the various ways in which customizable endonucleases can be used to introduce modifications into target genes. Customizable endonucleases trigger double-strand breaks in selected target sites of the plant genome. The DNA is then repaired via one of three major mechanisms, resulting in modifications at the target site: I, non-homologous end-joining (NHEJ) repair; II, microhomology-mediated end-joining (MMEJ) repair; and III, homologous recombination (HR). These mechanisms result in possible insertions, deletions, and/or substitutions of individual or multiple nucleotides. The size of the insertion or deletion is random following NHEJ-mediated DNA repair, whereas MMEJ and HR lead to predictable modifications and can thus be utilized for precise genome editing.