Unveiling the Genetic and Physiological Synergies of Iron and Sulfur Homeostasis in Durum Wheat: From Root to Grain.

Abstract

Fe deficiency is a major global challenge for agriculture. While high sulfur (S) supply can improve Fe nutrition in some grasses, the underlying mechanisms are poorly understood. This study investigated four genetically distinct durum wheat genotypes (Svevo, Karim, LcyE A^-B^-, and Svems16) to test the hypothesis that they employ different S-mediated strategies to maintain Fe homeostasis under varying Fe availability. Fe deficiency inhibited plant growth and induced chlorosis with genotypic differences in severity. Notably, high S mitigated chlorosis in Karim and promoted root development in most genotypes, especially Svems16. Ionomic analysis showed that Fe deficiency primarily drove nutrient shifts in roots, but adding S restored shoot ionomic profiles. Total S analysis revealed genotype-specific accumulation. Svevo showed consistently low S, possibly due to a sulfate transporter variant. Conversely, Karim exhibited elevated root S under combined stress, suggesting increased S channeling to phytosiderophore (PS) biosynthesis, supported by genotype-dependent PS release. Genotyping-by-sequencing identified variants in methionine metabolism and PS-related genes, offering molecular bases for the observed physiological differences. ATPS and OASTL activity patterns further confirmed the genotype-specific role of root S metabolism in Fe deficiency response. Grain ionomics revealed that LcyE A^-B^- enhanced Fe accumulation under combined high S and Fe deficiency, Svems16 under high S, while Karim, the most sensitive, had reduced grain Fe under deficiency. Our results highlight distinct, genotype-specific strategies for maintaining Fe homeostasis and identify promising targets for breeding programs aimed at improving nutrient use efficiency and biofortification in durum wheat.