Transcriptomic and physiological analyses revealed nicotianamine enhances wheat tolerance to excess manganese

Manganese (Mn) is an essential plant micronutrient but toxic at supra-optimal concentrations. Although nicotianamine (NA) biosynthesis is metal inducible, its specific role in Mn detoxification in wheat remains poorly characterized. Integrated transcriptomic and physiological analyses of Mn-tolerant (ET8, Carazinho) and Mn-sensitive (ES8, Egret) wheat near-isogenic lines and their parental cultivars under excess Mn revealed pronounced upregulation of genes encoding nicotianamine synthase (TaNAS), nicotianamine aminotransferase (TaNAAT), and putative Mn-NA transporters (TaYSL2, TaYSL6) in tolerant genotypes. This transcriptional response correlated with elevated NA accumulation in roots under Mn stress. Exogenous NA application enhanced Mn tolerance in hydroponically grown seedlings in a concentration-dependent manner, accompanied by reduced tissue Mn accumulation, and maintained homeostasis of essential cations (Ca, Mg, Fe, Zn, Cu) in both roots and shoots. Our findings demonstrate that NA biosynthesis and transport contribute to Mn tolerance by modulating Mn partitioning and metal ion homeostasis. We further propose candidate genes (TaNAS, TaNAAT, TaYSL2, TaYSL6) as potential targets for breeding Mn-tolerant wheat.