Genome Editing With CRISPR/Cas9 in Pinus Radiata (D. Don)

Abstract BackgroundTo meet increasing demand for forest-based products and protect natural forests from further deforestation requires increased productivity from planted forests. Genetic improvement of conifers by traditional breeding is time consuming due to the long juvenile phase and genome complexity. Genetic modification (GM) offers the opportunity to make transformational changes in shorter time frames but is challenged by current genetically modified organism (GMO) regulations. Genome editing, which can be used to generate site-specific mutations, offers the opportunity to rapidly implement targeted improvements and is globally regulated in a less restrictive way than GM technologies.ResultsWe evaluated U6 snRNA promoters from three different species that were able to drive expression of guide RNA (gRNA) for CRISPR/Cas9 genome editing in P. radiata . Using a single-copy cell wall gene GUX1 as a target, we have demonstrated genome editing using CRISPR/Cas9 in somatic embryogenic tissue and plantlets derived from the edited tissue. We generated biallelic INDELs with an efficiency of 15% using a single gRNA. Twelve percent of the transgenic embryogenic tissue was edited when two gRNAs were used and deletions of up to 1.3 kb were identified. However, the regenerated plants did not contain large deletions but had single nucleotide insertions at one of the target sites. We also assessed the use of CRISPR/Cas9 ribonucleoproteins (RNPs) for their ability to accomplish DNA-free genome editing in P . radiata. We chose a hybrid approach, with RNPs co-delivered with a plasmid-based selectable marker. A two-gRNA strategy was used which produced an editing efficiency of 33%, and generated INDELs, including large deletions. Using the RNP approach, deletions found in embryogenic tissue were also present in the plantlets. But, all plants produced using the RNP strategy were monoallelic.Conclusion We have demonstrated the generation of biallelic and monoallelic INDELs in the coniferous tree P. radiata with the CRISPR/Cas9 system using DNA and RNPs respectively. This opens the opportunity to apply genome editing in conifers to rapidly modify key traits of interest.