Genomics and Applied Biology 2024, Vol.15, No.4, 182-190 http://bioscipublisher.com/index.php/gab 184 Figure 1 Application of CRISPR/Cas9 system for developing elite variety with desirable improved traits in rice and its comparison with conventional crop breeding technique (Adopted from Zeb et al., 2022) 3.3 Key genes targeted by CRISPR/Cas9 for yield enhancement CRISPR/Cas9 technology has revolutionized the field of plant breeding by enabling precise and targeted modifications of the genome (Wang, 2024). Several key genes have been targeted using this technology to enhance yield traits in rice. For instance, the editing of OsPIN5b and GS3 genes has resulted in increased panicle length and grain size, respectively, leading to higher yields (Zeng et al., 2018). Additionally, the CLE genes in maize, which are involved in meristem size regulation, have been edited to create quantitative variations in yield-related traits, demonstrating the potential of similar approaches in rice (Liu et al., 2021b). The OsSAPgene, associated with drought stress response, has also been targeted to improve yield under adverse environmental conditions (Park et al., 2022) (Figure 2). These examples highlight the effectiveness of CRISPR/Cas9 in developing rice varieties with superior yield traits by precisely targeting and modifying specific genes. 4 Case Studies: CRISPR/Cas9-Mediated Improvements in Rice Yield 4.1 Increasing grain size and weight CRISPR/Cas9 technology has been effectively utilized to enhance grain size and weight in rice. A notable example is the editing of the Grain Size 3 (GS3) gene, which resulted in significant increases in grain length and weight. Specifically, the grain length and 1000-grain weight of the mutants were increased by 31.39% and 27.15%, respectively, compared to the wild type. This was achieved by targeting specific sites within the GS3 gene, leading to stable long-grain rice mutants with improved yield traits (Usman et al., 2021). Additionally, simultaneous editing of the GS3 gene along with other yield-related genes such as OsPIN5b has shown promising results in increasing panicle length and grain size, further contributing to higher yields (Zeng et al., 2020) (Figure 3). 4.2 Enhancing photosynthetic efficiency Improving photosynthetic efficiency is another critical area where CRISPR/Cas9 has shown significant potential. By knocking out the hexokinase gene OsHXK1, researchers have developed rice varieties with enhanced photosynthetic efficiency. The edited plants exhibited increased light saturation points, stomatal conductance, light tolerance, and overall photosynthetic products, leading to higher rice yields. Transcriptome analysis revealed that the expression of photosynthesis-related genes was significantly upregulated in the OsHXK1-CRISPR/Cas9 lines, underscoring the gene's role in regulating photosynthesis and yield (Zheng et al., 2021).
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