Nutrients are essential for life through intertwined perception, signaling, and metabolic processes. Plants have evolved complex systems to respond to and adapt to fluctuations in nutrients from scarcity to abundance in the soil.
Nitrate (N) and phosphorus (P) are the main macronutrients that can be metabolized into a variety of organic compounds that are essential for many biochemical processes. Studies on model plants have shown that nutrient acquisition is prioritized. For example, the phosphorus starvation response (PSR) is only activated when nitrate is available. Therefore, it is crucial to study how crops can effectively coordinate nitrogen and phosphorus utilization in complex environments.
On February 16, 2025, Jiewen Xing's team at China Agricultural University published a research paper titled "TaTCP6 is required for efficient and balanced utilization of nitrate and phosphorus in wheat" online in Nature Communications.
This study used the commonly used transgenic receptor "Fielder" in wheat as the object, and carried out hydroponic treatments under different nitrogen and phosphorus concentrations to obtain the root transcriptome under four environments.
Most important nitrate transporters and assimilation enzymes were identified to be highly expressed in high nitrogen environments and inhibited by low phosphorus. Most PSR genes were highly expressed only in high nitrogen and low phosphorus environments, indicating that nitrogen supply is essential for phosphorus starvation response.
Figure 1. Phenotype and transcriptome of wheat under different nitrogen and phosphorus concentrations. (Liu, et al., 2025)
Based on the nitrogen and phosphorus transcriptome, combined with the yeast one-hybrid results of nitrate-induced transcriptome and nitrate high-affinity transporter NRT2.1-6B4. This study identified a transcription factor TaTCP6 that is induced by nitrate.
Wheat materials with overexpression, knockout and self-driven expression of TaTCP6-SRDX fusion protein were constructed. The authors made it clear that it is regulated by nitrate and can directly bind to and activate a large number of nitrogen assimilation and growth and development-related genes. CUT&Tag experiments confirmed this conclusion.
Since TaTCP6 binding was rarely detected in the promoter of PSR genes, and most of them were found to be upregulated, combined with the results of yeast two-hybrid screening library of TaTCP6, it is speculated that TaTCP6 may achieve expression regulation of PSR genes and increase the inorganic phosphorus content of overexpressed plants through interaction with TaPHR2. Experiments such as Co-IP confirmed this hypothesis, and further studies found that TaTCP6 can interact with TaSPXs in a phosphorus-independent form.
Combining molecular biological experiments and genetic analysis, a new molecular mechanism was revealed: TaTCP6 competes with TaSPX1/4 to release TaPHR2, and also interacts with TaPHR2 to enhance the transactivation ability of downstream genes. Therefore, through the dual action of TaTCP6, the TCP6-SPX-PHR2 module activates the expression of PSR genes. Overexpression of TaSPX1 inhibits nitrogen utilization genes, especially under low phosphorus conditions. This process may be mainly achieved by inhibiting the functions of TaTCP6 and TaNLPs.
Field experiments showed that moderately increasing the expression of TaTCP6 can significantly increase the yield per plant of wheat under normal fertilization and reduced fertilization (low nitrogen and low phosphorus) environments.
Knocking out the homologous gene OsTCP6 of TaTCP6 in rice reduced the yield per plant of rice. Since the functions of TaTCP6/OsTCP6 and TaTCP19 reported in rice seem to be completely opposite, the authors speculate that this mechanism may be conserved in monocots, and TCP6 and TCP19 use an interesting redundant mechanism to ensure the adaptability and growth and development coordination of grains to complex nutrient environments.
Figure 2. Molecular mechanism model of TaTCP6 involved in coordinating nitrogen and phosphorus absorption and utilization. (Liu, et al., 2025)
In this study, the authors collected a series of transcriptome data of wheat seedlings under different nitrogen and phosphorus conditions. From these data, the authors identified a class I TCP transcription factor TaTCP6, which can respond to external nitrate and directly regulate nitrate absorption and assimilation. In addition, TaTCP6 interacts with TaSPXs and TaPHR2, releasing TaPHR2 from the TaSPXs-TaPHR2 complex and enhancing its transcriptional activation ability, thereby significantly improving the phosphorus utilization efficiency of wheat.
The research results provide important clues for a deeper understanding of the molecular mechanism of efficient synergistic utilization of nitrogen and phosphorus in wheat, and provide a new theoretical basis and technical ideas for the design and breeding of new nitrogen and phosphorus efficient wheat varieties.
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