Applications of CRISPR/Cas9 technology for targeted mutagenesis,gene replacement and stacking of genes in higher plants

Mutagenesis continues to play an essential role for understanding plant gene function and, in some instances, provides an opportunity for plant improvement. The development of gene editing technologies such as TALENs and zinc fingers has revolutionised the targeted mutation specificity that can now be achieved. The CRISPR/Cas9 system is the most recent addition to gene editing technologies and arguably the simplest requiring only two components; a small guide RNA molecule (sgRNA) and Cas9 endonuclease protein which complex to recognise and cleave a specific 20 bp target site present in a genome. Target specificity is determined by complementary base pairing between the sgRNA and target site sequence enabling highly specific, targeted mutation to be readily engineered. Upon target site cleavage, error-prone endogenous repair mechanisms produce small insertion/deletions at the target site usually resulting in loss of gene function. CRISPR/Cas9 gene editing has been rapidly adopted in plants and successfully undertaken in numerous species including major crop species. Its applications are not restricted to mutagenesis and target site cleavage can be exploited to promote sequence insertion or replacement by recombination. The multiple applications of this technology in plants are described.