Molecular Plant Breeding 2024, Vol.15, No.4, 178-186 http://genbreedpublisher.com/index.php/mpb 182 4 Yield Traits in Rice and Their Genetic Basis 4.1 Definition and importance of yield traits Yield traits in rice are critical agronomic characteristics that directly influence the productivity and economic value of rice crops. These traits include grain size, grain number, and panicle length, among others. Grain size, for instance, is a major determinant of rice yield and is a vital trait for both domestication and breeding efforts (Usman et al., 2020; Usman et al., 2021). Grain number per panicle and panicle length also significantly contribute to the overall yield, with higher numbers generally correlating with increased productivity (Huang et al., 2018; Zeng et al., 2020). The importance of these traits lies in their direct impact on the quantity of rice produced per unit area, which is essential for meeting the food demands of a growing global population. 4.2 Major yield-related genes in rice Several key genes have been identified that play crucial roles in determining yield traits in rice. For example, the Grain Size 3 (GS3) gene is known to regulate grain length, with mutations in this gene leading to increased grain size and weight (Zeng et al., 2020; Usman et al., 2021). Another important gene is Grain number 1a (Gn1a), which influences the number of grains per panicle. Mutations in Gn1a have been shown to enhance grain number, thereby boosting overall yield (Huang et al., 2018; Zhou et al., 2018). Additionally, the DENSE AND ERECT PANICLE1 (DEP1) gene is associated with panicle architecture, and its favorable alleles can lead to denser and more erect panicles, contributing to higher yield (Huang et al., 2018). 4.3 Genetic pathways influencing yield traits The genetic pathways influencing yield traits in rice are complex and involve multiple genes and regulatory networks. For instance, the CLAVATA-WUSCHEL pathway, which is regulated by CLE peptide signals, plays a significant role in controlling meristem size and, consequently, yield-related traits (Liu et al., 2021a). The OsSPL16/qGW8 gene, when edited using CRISPR/Cas9, has been shown to modulate the expression of pyruvate enzymes and cell cycle proteins, leading to increased grain size and yield (Usman et al., 2020). Furthermore, the OsPIN5b gene, which affects panicle length, and the OsMYB30 gene, which is involved in cold tolerance, have been successfully edited to produce rice varieties with improved yield and stress resistance (Zeng et al., 2020). These genetic pathways highlight the intricate network of interactions that govern yield traits and the potential of CRISPR/Cas9 technology to enhance these traits through precise genome editing. 5 CRISPR/Cas9 Strategies for Yield Trait Improvement 5.1 Gene knockout approaches Gene knockout strategies using CRISPR/Cas9 involve the targeted disruption of specific genes to enhance desirable traits in rice. This approach has been effectively utilized to improve various yield-related traits. For instance, the knockout of the Os8N3 gene in rice has been shown to confer enhanced resistance to Xanthomonas oryzae pv. oryzae, a significant pathogen, without affecting other agronomic traits (Kim et al., 2019). Similarly, the editing of the Oryza sativa Senescence-associated protein (OsSAP) gene has demonstrated improved drought resistance, which is crucial for maintaining yield under stress conditions (Park et al., 2022). These examples highlight the potential of gene knockout strategies in improving yield traits by enhancing resistance to biotic and abiotic stresses. 5.2 Gene knock-in strategies Gene knock-in strategies involve the precise insertion of beneficial genes into specific genomic locations to enhance yield traits. This method allows for the introduction of new functions or the enhancement of existing ones. For example, the insertion of genes that regulate grain size, such as the Grain Size 3 (GS3) gene, has resulted in rice mutants with significantly increased grain length and weight (Usman et al., 2021). This approach not only improves yield but also ensures the stable inheritance of these traits across generations. The ability to introduce specific genes with known beneficial effects makes gene knock-in strategies a powerful tool for yield improvement in rice breeding.
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