Rice Genomics and Genetics 2024, Vol.15, No.3, 121-131 http://cropscipublisher.com/index.php/rgg 123 2.3 Contributions to yield enhancement One of the most significant contributions of the SD1 gene to rice yield enhancement is its role in improving lodging resistance. The shorter, sturdier stems of SD1 mutants are less likely to lodge, even under adverse weather conditions or high nitrogen fertilization, thereby ensuring higher and more stable yields (Sasaki et al., 2002; Asano et al., 2007; San et al., 2020). This trait was a key factor in the success of the "green revolution" rice varieties, such as IR8, which dramatically increased rice production in the 1960s (Ashikari et al., 2002; Peng et al., 2021). The SD1 gene also contributes to yield enhancement by improving grain filling and the harvest index. The semi-dwarf varieties tend to allocate more resources to grain production rather than vegetative growth, resulting in a higher harvest index (the ratio of grain yield to total biomass) (Asano et al., 2007; Jia et al., 2020). Additionally, the improved light penetration into the canopy due to the more erect leaf inclination angle in SD1 mutants further enhances photosynthetic efficiency and grain filling (San et al., 2020). The SD1 gene plays a crucial role in rice plant architecture and yield enhancement by regulating gibberellin biosynthesis, influencing plant height and stem strength, and improving lodging resistance and grain filling. The widespread adoption of SD1 mutants has been a cornerstone of modern rice breeding, contributing significantly to global food security. 3The MOC1 Gene and Its Role in Rice 3.1 Genetic and molecular basis of MOC1 The MONOCULM1 (MOC1) gene plays a critical role in the regulation of rice tillering and overall plant architecture. Located on chromosome 6, MOC1 encodes a transcription factor that belongs to the GRAS protein family. This gene is essential for the initiation and development of tillers, which are the lateral branches that emerge from the base of the rice plant. Mutations or disruptions in MOC1 result in the monoculm phenotype, characterized by a single main culm with no tillers, demonstrating the gene's pivotal role in tiller formation and plant morphology (Yu et al., 2020). The MOC1 gene functions as a master regulator of tillering and branching in rice. It is expressed in the axillary meristems, where it activates the transcription of downstream genes involved in the initiation and outgrowth of tillers. MOC1 interacts with various hormonal pathways, including those of auxin and cytokinin, to modulate the balance between tiller bud dormancy and activation. This regulation ensures optimal tillering, contributing to the plant's ability to maximize light capture and nutrient use efficiency. 3.2 Impact on plant architecture The MOC1 gene directly influences the number of tillers a rice plant produces. By regulating the activation and growth of axillary buds, MOC1 determines the extent of tillering, which is a crucial component of rice plant architecture. Increased tillering, controlled by MOC1, leads to a bushier plant with more shoots, which can enhance photosynthetic capacity and potential grain production. Beyond tillering, MOC1 also impacts the overall root and shoot architecture of rice plants (Figure 2) (Shao et al., 2019). The gene's regulatory functions extend to the coordination of root growth patterns, ensuring a robust root system that can support the increased shoot biomass resulting from enhanced tillering. This integrated development of roots and shoots under the influence of MOC1 is vital for maintaining plant stability and nutrient uptake, which are essential for high yield performance. 3.3 Contributions to yield enhancement One of the primary contributions of the MOC1 gene to rice yield enhancement is through the increase in tiller and panicle numbers. More tillers typically result in more panicles, each of which can produce grains. The effective management of tillering via MOC1 ensures that these additional panicles are well-developed and capable of supporting a high grain load, thereby directly contributing to increased grain yield per plant (Deng et al., 2022).
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