Rice Genomics and Genetics 2024, Vol.15, No.3, 142-152 http://cropscipublisher.com/index.php/rgg 144 2.3 Molecular mechanisms and pathways Understanding the molecular mechanisms underlying nutrient synthesis and regulation is critical for developing nutritionally enhanced rice varieties. The synthesis of nutrients in rice is controlled by a complex network of genes. For example, the expression of genes involved in starch and protein synthesis significantly impacts the nutritional quality of rice grains. Studies have profiled the expression patterns of genes involved in these pathways, providing insights into their regulation and potential targets for genetic manipulation (Ajmera, 2017). Transcription factors play a pivotal role in regulating nutrient metabolism in rice. These proteins can activate or repress the expression of genes involved in nutrient synthesis, thereby influencing the nutritional content of the rice grains. Advances in functional genomics have identified several key transcription factors that regulate these processes, offering new avenues for improving the nutritional quality of rice through genetic engineering (Duan et al., 2022). The genetic factors affecting the nutritional content of rice are multifaceted, involving natural genetic diversity, QTLs, and molecular mechanisms. By leveraging this knowledge, breeding programs can develop rice varieties with enhanced nutritional profiles, addressing global nutritional deficiencies and improving public health. 3 Genetic Factors Affecting Yield 3.1 Rice yield composition Grains per panicle is a key determinant of rice yield. Genetic factors influencing this trait have been extensively studied. For example, the DEP1 locus has been identified as a major quantitative trait locus (QTL) that increases grain number per panicle by enhancing meristem activity6. Furthermore, constitutive expression of cell wall invertase genes has been shown to increase grain number and thus overall grain yield (Pujar et al., 2020). Particle size and weight are also important factors affecting yield. The GS2 locus encoding growth regulatory factor 4 (OsGRF4) has been identified as a key genetic determinant of grain size. Rare alleles of GS2 result in larger cells and increased cell numbers, thereby increasing grain weight and yield. Furthermore, studies have shown that grain weight is highly correlated with yield, and this relationship is consistent across various rice varieties. Plant height and biomass are closely related to yield. QTL analyzes have identified several loci affecting these traits. For example, five QTL related to plant height were detected, some of which also contributed to grain yield and biomass. The relationship between plant height and yield is complex, with some QTL contributing to both traits, while other QTL mainly affect plant height5. Furthermore, biomass production and allocation are critical for yield, and specific QTL were identified for these traits. 3.2 Genetic determinants of yield High-yielding rice varieties often have specific genetic markers that contribute to their superior performance. For example, the DEP1 locus is common in many high-yielding Chinese rice varieties and is associated with increased grain yield. Likewise, the GS2 locus has been introduced into various rice varieties to improve grain weight and yield (Das et al., 2020). These genetic markers provide valuable tools for breeding programs aimed at developing high-yielding rice varieties. QTL play a vital role in yield improvement by regulating various yield-related traits. For example, QTL related to grain yield, biomass, and harvest index have been identified, with some of these QTL colocalizing on specific chromosomes, suggesting a genetic basis for increased yield through enhanced biomass or increased harvest index5. In addition, QTL affecting grain yield and nutritional composition have been identified, with certain regions on chromosomes 6 and 10 being particularly important. 3.3 Molecular pathways affecting yield Photosynthetic efficiency is a key factor affecting yield, Genetic engineering methods target genes involved in photosynthesis to increase yields. For example, constitutive expression of cell wall invertase genes has been shown to increase photosynthetic efficiency, thereby increasing grain yield and starch content (Li et al., 2013). Stress resistance genes also play an important role in determining yield, especially under adverse environmental conditions. Although specific stress tolerance genes are not highlighted in the data presented, it is known that breeding for stress tolerance can significantly improve yield stability and overall productivity.
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