Triticeae Genomics and Genetics, 2025, Vol.16, No.6, 269-277 http://cropscipublisher.com/index.php/tgg 273 key is to keep up with the activity of metabolic enzymes, such as glutamine synthase and alanine aminotransferase. Once the enzyme activity increases, it indicates that the nitrogen assimilation function of the root system is also more active. This point has been supported in the studies of Dweikat and Clemente (2017) and Pena et al. (2017), and Zameer et al. (2025) also emphasized the positive impact of this physiological change on plants' tolerance to low-nitrogen environments. 5.3 Field trials: yield, nitrogen recovery efficiency, and NUE comparison No matter how well genetically modified materials perform in the laboratory, they eventually have to be tested in the fields. In multiple studies, wheat materials that expressed nitrogen metabolism-related genes in their roots demonstrated higher grain yield and nitrogen recovery efficiency than the control group. Materials with the introduction of barley alanine aminotransferase even improved overall nitrogen use efficiency and biomass under field conditions (Pena et al., 2017). However, things are not always linear. Sometimes, environmental factors such as climate, soil, and management methods can devalue these phenotypic results. Therefore, as Chachar et al. (2022) suggested, multi-point and repetitive field trials have become a necessary step to determine whether this material is worth promoting or not. 6 Case Studies 6.1 Study on improving nitrogen uptake efficiency using OsRCc3 promoter to drive TaNRT2.1 To discuss the improvement of nitrogen absorption efficiency in wheat, it is advisable to start with the experience of rice. Some studies have used OsRCc3, a root-specific promoter, to drive the expression of TaNRT2.1. Although there is not much direct data in wheat in this regard, this cross-species gene combination is not a new attempt. When rice nitrate transporters like OsNRT1.1A are overexpressed in wheat, they show remarkable adaptability. Especially in a low-nitrogen environment, the root system grows better, the absorption efficiency increases, and the grain yield naturally rises (Wang et al., 2024). From this perspective, if promoters like OsRCc3 can precisely regulate the expression of TaNRT2.1 in the roots, they might be able to open up a new situation in nitrogen utilization efficiency. 6.2 Field evaluation of TaGS1 transgenic wheat constructed with ZmRCP1 promoter The root promoter ZmRCP1, derived from corn, is used to drive TaGS1 expression, with the aim of enhancing nitrogen assimilation efficiency. Ultimately, the key to TaGS1, the glutamine synthase, lies in whether it is efficient in treating ammonium. Although related field experiments are not overwhelming, existing studies have shown that this root-targeted expression strategy can indeed increase enzyme activity and thereby drive the increase of biomass (Tiong et al., 2021; Zhang et al., 2021). Although the specific field performance data of ZmRCP1+TaGS1 is not yet abundant, from the trend perspective, it is worth delving deeper to achieve higher output without increasing nitrogen input. 6.3 Performance analysis of transgenic wheat under low-nitrogen conditions by the Chinese academy of agricultural sciences What should be done in a low-nitrogen environment? A series of experiments conducted by the Chinese Academy of Agricultural Sciences have provided their answer. Some schemes are traditional transgenic pathways, such as introducing OsNRT1.1A into wheat to ensure it has long roots and well-fed seeds even in nitrogen-deficient fields. Some have employed more "clean" gene editing techniques, such as knockout of TaARE1, which have also achieved the goals of delaying aging and increasing yield (Figure 2) (Zhang et al., 2021; Wang et al., 2024). Interestingly, no matter which technical route it is, the thinking points to a consensus: the root is the key to regulating nitrogen utilization efficiency. The future direction of improvement is likely to focus on the roots rather than merely solving the problem by increasing fertilization. 7 Environmental Impact and Biosafety Assessment 7.1 Potential effects of exogenous genes on non-target tissues and ecosystems Although the use of root-specific promoters is aimed at confining the expression of exogenous genes to the underground part as much as possible, this strategy cannot completely eliminate the possible concerns about the ecosystem. Could the above-ground tissues "mistakenly trigger" the expression mechanism? This is a question
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