Advances in genome editing in plants within an evolving regulatory landscape, with a focus on its application in wheat breeding

Population growth, diminishing resources and climate change are some of the many challenges that agriculture must address
to satisfy the needs of the global population whilst ensuring the safety and nutritional value of our food. Wheat (Triticum
aestivum) is tremendously important for human nutrition, providing starch (and, therefore, energy), fibre, protein, vitamins, and micronutrients. It is the second most widely grown crop behind maize (Zea mays), with 808 million tonnes of grain being produced in 2021–2022. In comparison, the production figure for 1961 was 222 million tonnes, and there have been similar increases for maize and rice (Oryza sativa). World population over the same period has increased from just over 3 billion to just over 8 billion, a stark reminder of just how important increased crop production has been in maintaining food security over that period, and for these cereals it has been achieved without additional land use. Plant breeding has played an important part in enabling crop production to keep increasing to meet demand and this will have to continue through the coming decades. Innovative technologies will play a part in that, and here we review how the new technology of genome editing is being applied in crop genetic improvement, with a focus on wheat. We cover oligonucleotide-directed mutagenesis and the use of site-directed nucleases, including meganucleases (MegNs), zinc-finger nucleases (ZFNs), transcription activator-like
effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) nucleases. We describe established genome editing strategies, mainly involving gene ‘knockouts’, and the new applications of base and prime editing using CRISPR/Cas. We also discuss how genome editing for crop improvement is developing in the context of an evolving regulatory landscape.