Bioscience Methods 2025, Vol.16, No.4, 204-217 http://bioscipublisher.com/index.php/bm 206 harvest index) is affected by the source-sink characteristics of the variety: nitrogen-efficient genotypes often have greater late assimilation capacity and slower leaf senescence rate, which significantly increases the dry matter and nitrogen accumulation after heading. For example, nitrogen-efficient and high-yield varieties still maintain a high leaf area index and green functional leaves at maturity, and have more nitrogen assimilated later to supply grains than ordinary varieties. The transportation and redistribution process of nitrogen in rice plants between sources (assimilation organs such as leaves) and sinks (storage organs such as grains) is complex and efficient, and is a key factor in determining the final yield and quality. 2.3 Synergistic relationship between nitrogen metabolism and growth regulation The nitrogen metabolism process of rice is closely coupled with carbohydrate metabolism and growth and development. Nitrogen assimilation requires a large amount of adenosine triphosphate (ATP) and reducing power, and its energy and carbon skeleton come from carbon metabolites provided by photosynthesis and respiration. At the same time, the nitrogen supply level will significantly affect the carbon allocation of plants: sufficient nitrogen promotes tillering and leaf growth, and increases the proportion of photosynthetic products used to build assimilation products such as proteins; while under nitrogen limitation, plants tend to reduce new leaf growth and increase carbon allocation to the root system to enhance the ability to obtain nitrogen. Studies have shown that maintaining a suitable C/N balance is crucial for normal crop growth and yield formation (Wang et al., 2020). There is a molecular regulatory network in plants that integrates carbon and nitrogen signals. For example, when nitrogen nutrition is sufficient, the increased abundance of amino acids will feedback inhibit certain steps in carbon assimilation, thereby avoiding excessive carbon accumulation; conversely, when nitrogen is deficient, plants enhance the nitrogen absorption capacity of the root system by increasing the distribution of carbohydrates in the roots. Multiple transcription factors are involved in coordinating C-N metabolism, such as Dof and bZIP factors, which sense the levels of carbon/nitrogen metabolites and regulate the expression of downstream enzyme genes to adapt to changes in nutritional status. Overexpression of maize Dof1 transcription factor can improve rice photosynthesis and the flow of carbon to nitrogen assimilation pathways, significantly enhancing plant growth and nitrogen accumulation under low nitrogen conditions. Another example is factors such as OsNAC42, which can simultaneously upregulate nitrate transport and growth-related genes to achieve the effect of maintaining a higher growth rate under low nitrogen. Therefore, nitrogen metabolism and plant growth and development are closely coordinated through a complex signaling network. When optimizing cultivation management, the effects of nitrogen supply on growth processes such as tillering and heading should be comprehensively considered to achieve synchronous coordination of nutrient supply and crop growth requirements (Du et al., 2013). 3 Expression and Regulation of Genes Related to Nitrogen Use Efficiency in Rice 3.1 Role of key genes in nitrogen utilization With the deepening of rice genome functional research, a series of key genes affecting nitrogen absorption and utilization have been identified. Functional gene mutations in nitrogen transport and assimilation pathways lead to differences in plant NUE. For example, the nitrate transport gene OsNRT1.1B has functional differences due to allelic variation between indicaand japonicasubspecies: Studies have found that the indica rice OsNRT1.1Ballele increases the root system's NO3 - uptake activity and root-leaf nitrogen transport efficiency, so that the nitrogen absorption and grain yield of the near-isogenic japonica rice are significantly increased after the introduction of indica rice OsNRT1.1B (Lee, 2021). Therefore, OsNRT1.1B is considered to be one of the important sites controlling rice nitrogen efficiency (Tang et al., 2019). Similarly, in terms of ammonium nitrogen absorption, the root high-affinity ammonium transporter OsAMT1.2 plays a key role. Some studies have achieved higher growth and grain yield of rice under low nitrogen conditions by simultaneously enhancing the expression of OsAMT1.2 and GOGAT enzyme genes. The rate-limiting enzyme genes of nitrogen assimilation metabolism have a significant effect on NUE. The glutamine synthetase gene OsGS1;1 is mainly expressed in roots and old leaves, responsible for assimilating absorbed or transported NH4 + into glutamine, and is a key enzyme in the nitrogen recycling process. The OsGS1;1 knockout mutant showed poor growth and decreased nitrogen content in the grain, indicating that this gene is indispensable for nitrogen redistribution and yield formation. However, simply overexpressing nitrogen assimilation enzymes does not necessarily increase NUE. For example, overexpression of
RkJQdWJsaXNoZXIy MjQ4ODYzNA==