Towards a Highly Efficient Gene Targeting System in Higher Plants

Gene targeting (GT) via homologous recombination (HR) is a powerful tool for the precise modification of the target gene. In spite of many efforts, GT frequency in higher plants is still low. Ail efficient transformation system, enhancement of the HR and efficient selection of the gene targeted cells are thought to be essential for the development of ail efficient GT system in plants. Recent reports showed that the open chromatin state of host cells and/or specific induction of the DNA double strand breaks (DSBs) in the gene of interest are important to improve HR and GT. RAD54 is involved in chromatin remodeling during HR. Chromatin assembly factor 1 (CAF-1) is involved in nucleosome assembly after DNA replication. Enhancement of RAD54 function and suppression of the CAF-1 function are expected to induce the open chromatin state in plant cells which Could induce HR. Zinc finger nuclease (ZFN), an artificial endonuclease composed of zinc finger domains and a nuclease domain, induce DSBs at the target sequence and enhance GT. In the next step, determining how to apply these potential effectors is a key to establish an efficient GT system.