Combined Use of Unidirectional Site-Specific Recombination System and CRISPR-Cas Systems for Plant Genome Editing

Site-specific recombination (SSR) systems have been extensively used for controlled genome modification in eukaryotic cells, especially for DNA excision and DNA site-specific integration. Unidirectional SSR systems are particularly attractive for efficient site-specific gene integration because of their irreversible recombination activities. Bxb1-att is one such unidirectional SSR system, which has emerged as a molecular tool for eukaryotic genome manipulation. We will review the discovery, development, and current applications of the Bxb1-att system with an emphasis on utility in plants. We provide perspectives on future applications using dual integrase cassette exchange for precise gene integration at a specific locus. Finally, potential applications of combining unidirectional SSR systems with newly developed genome-editing tools (e.g., CRISPR-Cas9) will be explored to enhance capabilities for precise locus-specific gene integration into plant genomes.