Rice grain yield and quality improvement via CRISPR/Cas9 system: an updated review

Rice (Oryza sativa L.) is an important staple food crop worldwide. To meet the growing nutritional requirements of the increasing population in the face of climate change, qualitative and quantitative traits of rice need to be improved. During recent years, genome editing has played a great role in the development of superior varieties of grain crops. Genome editing and speed breeding have improved the accuracy and pace of rice breeding. New breeding technologies including genome editing have been established in rice, expanding the potential for crop improvement. Over a decade, site-directed mutagenesis tools like Zinc Finger Nucleases (ZFN), Transcriptional activator-like Effector Nucleases (TALENs), and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) System were used and have played a great role in rice yield and quality enhancement. In addition, most recently other genome editing techniques like prime editing and base editors have also been used for efficient genome editing in rice. Since rice is an excellent model system for functional studies due to its small genome and close synthetic relationships with other cereal crops, new genome-editing technologies continue to be developed for use in rice. Genomic alteration employing genome editing technologies (GETs) like CRISPR/Cas9 for reverse genetics has opened new avenues in agricultural sciences such as rice yield and grain quality improvement. Currently, CRISPR/Cas9 technology is widely used by researchers for genome editing to achieve the desired biological objectives, because of its simple targeting, easy-to-design, cost-effective, and versatile tool for precise and efficient plant genome editing. Over the past few years many genes related to rice grain quality and yield enhancement have been successfully edited via CRISPR/Cas9 technology method to cater to the growing demand for food worldwide. The effectiveness of these methods is being verified by the researchers and crop scientists worldwide. In this review we focus on genome-editing tools for rice improvement to address the progress made and provide examples of genome editing in rice. We also discuss safety concerns and methods for obtaining transgene-free crops.