Cas9-Mediated Targeted Mutagenesis in Plants

Genome engineering technologies enable targeted mutations to be induced at almost any location in plant genomes. In particular, Cas9 nucleases use easily recoded RNA guides to target user-defined sequences and generate double-stranded breaks (DSB) that are then repaired by the cell's endogenous repair mechanisms. Incorrect repair results in mutations at the target. When the targets are in coding sequences, this often results in loss-of-function mutations. In this chapter, we describe a method to rapidly design and assemble RNA-guided Cas9 constructs for plants and test their ability to induce mutations at their intended targets in rapid assays using both Agrobacterium-mediated transient expression and PEG-mediated DNA delivery to protoplasts, the latter of which can be adapted to a wide range of plant species. We describe a PCR-based method for detecting mutagenesis and outline the steps required to segregate the Cas9 transgene from the targeted mutation to enable the production of transgene-free mutated plants. These techniques are amenable to a range of plant species and should accelerate the application of Cas-9-mediated genome engineering for basic plant science as well as crop development.