Gene Editing in Polyploid Crops: Wheat, Camelina, Canola, Potato, Cotton, Peanut, Sugar Cane, and Citrus

Polyploid crops make up a significant portion of the major food and fiber crops of the world and include wheat, potato, cotton, apple, peanut, citrus, and brassica oilseeds such as rape, canola, and Camelina. The presence of three sets of chromosomes in triploids, four sets in tetraploids, and six sets in hexaploids present significant challenges to conventional plant breeding and, potentially, to efficient use of rapidly emerging gene and genome-editing systems such as zinc finger nucleases, single-stranded oligonucleotides, TALE effector nucleases, and clustered regularly interspaced short palindromic repeats (CRISPR/Cas9). However, recent studies with each of these techniques in several polyploid crops have demonstrated facile editing of some or all of the genes targeted for modification on homeologous chromosomes. These modifications have allowed improvements in food nutrition, seed oil composition, disease resistance, weed protection, plant breeding procedures, and food safety. Plants and plant products exhibiting useful new traits created through gene editing but lacking foreign DNA may face reduced regulatory restrictions. Such plants can be obtained either by simply selecting for null segregants that have lost their editing transgenes during plant breeding or, even more attractively, by delivery of biodegradable Cas9/sgRNA ribonucleoprotein complexes (i.e., no DNA) into plant cells where they are expressed only transiently but allow for efficient gene editing-a system that has been recently demonstrated in at least two polyploid crops. Such systems that create precise mutations but leave no transgene footprint hold potential promise for assisting with the elimination or great diminution of regulatory processes that presently burden approvals of conventional transgenic crops.