On February 16, 2025, the research team led by Academician Qixin Sun from the College of Agronomy and Biotechnology at China Agricultural University published a paper in Nature Communications titled “TaTCP6 is required for efficient and balanced utilization of nitrate and phosphorus in wheat.” All plant growth experiments in this study were conducted in Jiupo plant growth chambers.
This study used the commonly employed wheat cultivar “Fielder” as a model and conducted hydroponic treatments under varying nitrogen and phosphorus concentrations, obtaining root transcriptomes under four environmental conditions. The results identified that most key nitrate transporters and assimilation enzymes were highly expressed under high-nitrogen conditions but were inhibited under low-phosphorus conditions. Interestingly, most phosphate starvation response (PSR) genes were highly expressed only under high-nitrogen and low-phosphorus environments, indicating that nitrogen availability is essential for triggering the phosphorus starvation response.
The research used wheat “Fielder” as a model in hydroponic treatments under varying nitrogen and phosphorus conditions to generate root transcriptomes under four distinct environments. The findings showed that key nitrate transporters and assimilation enzymes were primarily induced under high-nitrogen conditions but suppressed by low-phosphorus levels. Most PSR genes were upregulated predominantly under high-nitrogen and low-phosphorus conditions, suggesting that nitrogen supply is crucial for activating the phosphorus starvation response.
Figure 1:Wheat phenotypes and transcriptomes under different nitrogen and phosphorus treatments
Based on the nitrogen-phosphorus transcriptomes, combined with nitrate-induction transcriptome data and yeast one-hybrid screening results for the high-affinity nitrate transporter NRT2.1-6B4, the study identified a nitrate-inducible transcription factor, TaTCP6. Wheat lines overexpressing, knocking out, and expressing a TaTCP6-SRDX fusion protein under its native promoter were generated. The research confirmed that TaTCP6 is regulated by nitrate and directly binds to and activates numerous nitrogen assimilation and growth-related genes, a conclusion further supported by CUT&Tag experiments.
Figure 2: TaTCP6 directly binds and regulates nitrogen assimilation and development-related genes
Although TaTCP6 showed limited direct binding to PSR gene promoters, the expression of many PSR genes was found to be upregulated. Yeast two-hybrid assays suggested that TaTCP6 may regulate PSR gene expression via interaction with TaPHR2, contributing to increased inorganic phosphate levels in overexpression lines. Co-IP and additional experiments validated this hypothesis. Further mechanistic studies revealed that TaTCP6 also interacts with TaSPX proteins in a phosphorus-independent manner. Integrating molecular biology experiments and genetic analysis, the study elucidated a novel mechanism: TaTCP6 competes with TaSPX1/4 to release TaPHR2 from the TaSPXs-TaPHR2 complex and also interacts directly with TaPHR2, enhancing its transcriptional activation capability. Through this dual mechanism, the TaTCP6-SPX-PHR2 module activates PSR gene expression. Moreover, TaSPX1 overexpression was shown to suppress nitrogen utilization genes, particularly under low-phosphorus conditions, likely through inhibition of TaTCP6 and TaNLPs.
Field trials demonstrated that moderately increasing TaTCP6 expression significantly enhanced wheat yield per plant under both normal fertilization and reduced fertilization (low-nitrogen and low-phosphorus) conditions. In rice, knockout of the TaTCP6 homolog, OsTCP6, led to decreased yield per plant. Given that TaTCP6/OsTCP6 appears to function oppositely to the previously reported OsTCP19, the authors speculate that this mechanism may be conserved in monocotyledons, with TCP6 and TCP19 forming a redundant system to ensure cereals’ adaptation to complex nutrient environments and balanced growth and development.
Figure 3: Molecular model of TaTCP6’s role in coordinating nitrogen and phosphorus utilization
In this study, we collected a series of transcriptomic datasets from wheat seedlings under varying nitrogen and phosphorus conditions. From these datasets, we identified a class I TCP transcription factor, TaTCP6, that responds to external nitrate and directly regulates nitrate uptake and assimilation. Furthermore, TaTCP6 interacts with TaSPXs and TaPHR2, displacing TaPHR2 from the TaSPXs-TaPHR2 complex and enhancing its transcriptional activity, thereby significantly improving phosphorus use efficiency in wheat. These findings provide critical insights into the molecular mechanism underlying coordinated nitrogen and phosphorus utilization in wheat and offer a new theoretical framework and technical approach for the breeding of wheat varieties with enhanced nitrogen and phosphorus use efficiency.