| Abstract |
Nitrogen is a crucial macronutrient for plant growth, supplied in agroecosystems primarily as nitrate and ammonium. However, inefficient nitrogen use causes significant environmental losses in wheat, where only 48% of applied nitrogen is converted into biomass, but stabilized ammonium-based fertilization offers a promising strategy to reduce losses and enhance sustainability. Ammonium nutrition can confer agronomic benefits, including improved grain quality and stress tolerance in wheat, but high ammonium concentrations can be toxic, impairing plant growth and triggering physiological and molecular defense responses. This study aimed to investigate ammonium tolerance within a diverse panel of hexaploid winter wheat ( Triticum aestivum L.) accessions from the Gediflux collection. Hydroponic screening revealed that while most wheat varieties preferred ammonium-nitrate, few genotypes exhibited superior biomass production under ammonium-rich conditions. RNA-seq analysis of two contrasting genotypes—one tolerant and one susceptible—uncovered distinct gene regulation patterns in the tolerant cultivar. Notably, at the leaf level, genes encoding chlorophyll-binding proteins and Rubisco were significantly upregulated, potentially enhancing photosynthetic capacity and biomass yield. Additionally, key genes involved in abscisic acid signaling, including PYL4, PYL5, and PYL6, were upregulated, suggesting a crucial role in chloroplast protection and stress adaptation. To mitigate ammonium toxicity, the tolerant cultivar downregulated ammonium transport and storage-related genes, such as AMT2, CAP1, and TIP2;3, indicating a controlled ammonium homeostasis mechanism that limits excessive uptake and vacuolar sequestration. In roots, auxin-responsive genes were predominantly upregulated in the tolerant cultivar, with ARF6, ARF10, ARF16, and ARF17 potentially contributing to root system reorganization for improved ammonium tolerance. Ammonium nutrition significantly influenced transcriptional regulation across roots and leaves, with the tolerant genotype exhibiting a stronger root response and increased involvement in trichome morphogenesis, shoot development, hormonal signaling, and stress adaptation. K-means clustering identified differentially expressed transcription factors, including bZIP and WRKY-domain TFs associated with stress signaling, as well as nitrogen metabolism-related TFs such as ERF2 and HRE1. These findings provide novel insights into the molecular mechanisms underlying ammonium tolerance in wheat, highlighting potential targets for breeding varieties with enhanced nitrogen use efficiency and stress resilience. |
