Precision genome editing of crops for improved disease resistance.

Genome editing (GE) technologies allow rapid trait manipulation in crop plants. Disease resistance is one of the best test cases for this technology because it is usually monogenic and under constant challenge by rapidly evolving pathogens. Classical methods suffer from severe bottlenecks in discovery of new resistance (R) genes and their incorporation into elite varieties, largely because they are identified in landraces and species with limited sexual compatibility, and may last only a few years before losing effectiveness. Most plant R genes encode receptors located externally on the plasma membrane (receptor proteins and receptor kinases) or internally as NOD-like receptors (NLR). Both have well defined molecular interactions with activating pathogen ligands which are virulence proteins known as effectors. As structural data for R-effector interactions accumulate, promising strategies for rational manipulation of binding specificities are emerging. This offers the potential to change elite varieties directly rather than through 10-20 years of crossing. Successful application of GE is already evident in mutation of susceptibility (S) genes required for infection. GE is in its infancy with only four modified organisms grown currently in the US. The Anglosphere and Japan seem more open to deployment of these technologies, with the European Union, Switzerland and New Zealand being notably more conservative. Consumers are not well informed on the differences between GE and classical genetic modification (GM). The possibility that minor GE changes will not be regulated as GM offers the hope that current bottlenecks to resistance breeding can be eased.