CRISPR/Cas9-Mediated Targeted Mutagenesis in Upland Cotton (Gossypium hirsutum L.)

The clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR associated (Cas)9 protein system has emerged as a simple and efficient tool for genome editing in eukaryotic cells.  It has been shown to be functional in several crop species, yet there are no reports on the application of this or any other genome editing technologies in the cotton plant.  Cotton is an important crop that is grown mainly for its fiber, but its seed also serves as a useful source of edible oil and feed protein.  Most of the commercially-grown cotton is tetraploid, thus making it much more difficult to target both sets of homeologous alleles.  Therefore, in order to understand the efficacy of the CRISPR/Cas9 system to target a gene within the genome of cotton, we made use of a transgenic cotton line previously generated in our laboratory that had a single copy of the green fluorescent protein (GFP) gene integrated into its genome.  We demonstrated the use of this powerful new tool in targeted knockout of a GFP gene residing in the cotton genome.  By following the loss of GFP fluorescence, we were able to observe the cells that had undergone targeted mutations as a result of CRISPR/Cas9 activity.  In addition, we provide examples of the different types of indels obtained by Cas9-mediated cleavage of the GFP gene, guided by three independent sgRNAs.  The results provide useful information that will help us target important native genes in the cotton plant in future.