Towards DNA-free CRISPR/Cas9 genome editing for sustainable oil palm improvement

The CRISPR/Cas9 genome editing system has been in the spotlight compared to programmable nucleases such as ZFNs and TALENs due to its simplicity, versatility, and high efficiency. CRISPR/Cas9 has revolutionized plant genetic engineering and is broadly used to edit various plants' genomes, including those transformation-recalcitrant species such as oil palm. This review will comprehensively present the CRISPR-Cas9 system's brief history and underlying mechanisms. We then highlighted the establishment of the CRISPR/Cas9 system in plants with an emphasis on the strategies of highly efficient guide RNA design, the establishment of various CRISPR/Cas9 vector systems, approaches of multiplex editing, methods of transformation for stable and transient techniques, available methods for detecting and analyzing mutations, which have been applied and could be adopted for CRISPR/Cas9 genome editing in oil palm. In addition, we also provide insight into the strategy of DNA-free genome editing and its potential application in oil palm.