Editorial: New Genome Editing Tools and Resources: Enabling Gene Discovery and Functional Genomics

John Innes Centre, Norwich Research Park, Norwich, United Kingdom, State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, China, Department of Plant and Microbial Biology, University of Minnesota, St. Paul, MN, United States, Center for Precision Plant Genomics, University of Minnesota, St. Paul, MN, United States, Center for Genome Engineering, University of Minnesota, St. Paul, MN, United States, Division of Plant Sciences, Bond Life Sciences Center, University of Missouri, Columbia, MO, United States

Length in Rice." The authors report that the efficiency of FnCas12a-mediated editing depends on the length of the crRNA guide sequence. Altering the length of the crRNA changed the frequency with which large deletions could be obtained, indicating that this approach could fine-tune the editing outcome. The two papers describing the use of Cas12a add to the current literature demonstrating the high potential and versatility of this nuclease family (Bandyopadhyay et al., 2020).
In addition to single and multiple targeted gene knock-outs, there is a need to make other, specific targeted changes in plant genomes. Where a single base change is required, then base editing approaches may be appropriate ( Figure 1). However, where more than one base change is required, the new technique of prime editing may be used. In the paper "Spelling Changes and Fluorescent Tagging with Prime Editing Vectors for Plants," Wang et al. describe a set of easy-to-use vectors for prime editing in both dicot and monocot species. Generally, the size of insertion achieved by prime editing is small (Lin et al., 2020), but Wang et al. showed in their paper that it is possible to insert 66 bp, the largest reported to date. To make even larger genomic insertions at a precise location, gene targeting is required. The targeted insertion of large sequences or entire genes is technically challenging, and efficiencies are generally low (Dong and Ronald 2021). In the paper by Lawrenson et al. "In-planta Gene Targeting in Barley using Cas9 with and without Geminiviral Replicons," successful gene targeting in barley is described, with an mCherry marker gene being inserted at the target genomic locus.
As well as tools that expand the range of possible genome editing applications, ways to improve the speed and efficiency of genome editing systems have been examined. The process of plant genome editing can be time consuming, as there is generally a need for regeneration of plants from tissue culture. It is important, therefore, to have confidence that specific genome editing components will work. Nasti et al. in their paper "Fast-TrACC: A Rapid Method for Delivering and Testing Gene Editing Reagents in Somatic Plant Cells" address this issue. They describe a system that uses a luciferase reporter to provide a readout of the efficiency of Agrobacteriummediated delivery of genome editing reagents. The ability to test sgRNAs before attempting plant genome editing can save valuable time.
Often it is the generation time of a crop plant that limits fast progress in genome editing. In certain crops, rapid flowering lines have been developed. Fast-flowering minimaize is one such example (McCaw et al., 2016). As well as the fast-flowering phenotype, mini-maize also needs to be amenable to transformation to make it valuable for rapid genome editing applications. In the paper by McCaw et al. in this research topic, "Development of a Transformable Fast-Flowering Mini-Maize as a tool for Maize Gene Editing," the authors describe development of a fast-flowering mini-maize that is also amenable to transformation and editing at efficiencies up to 17 and 79%, respectively, with a seed to T1 seed time of 5.5 months compared to over 9 months for other genotypes.
In summary, this collection of papers highlights some exciting recent developments in provision of CRISPR/Cas tools and resources. These enhanced resources are poised to make a major contribution to more efficient and rapid gene discovery and functional characterization.