Iron-deficiency response and differential expression of iron homeostasis related genes in spring wheat (Triticum aestivum) mutant lines with increased grain iron content

Iron (Fe) is essential for plant growth and human health. Fe deficiency reduces yield and quality traits of wheat (Triticum aestivum L.). Grains of modern bread wheat varieties contain low levels of Fe, and Fe uptake and translocation in wheat grown in Fe conditions have not been studied in detail. This study investigates Fe homeostasis and biofortification in genetically stable spring wheat Almaken and Zhenis M5 mutant lines, developed with 200 Gy for higher grain Fe content. Mutant lines and parents were analysed for the expression of genes involved in Fe homeostasis under normal and deficient Fe. Wheat homologues of genes that participated in phytosiderophore (PS) synthesis and transport were significantly upregulated in the Fe-limited roots of Almaken M/1 and both Zhenis M/2 mutant lines, emphasising the role of deoxymugineic acid (DMA) in iron acquisition. The combined overexpression of SAMS, NASI, TaNAAT, DMAS and TOM was also revealed in the roots of Almaken M/1 and both Zhenis M5 mutant lines, suggesting their involvement in PS synthesis, Fe chelation and transport. Under Fe deficiency, levels of TaYS1A encoding the wheat homologues of the metal-NA transporter YSL, also showed 2.6-, 5.1- and 5.9-fold increases in the roots of Almaken M/1 and both Zhenis M5 mutant lines, respectively. Vacuolar iron transporters (VIT2), natural resistance associated-macrophage protein (NRAMP) genes and the transcription factor basic-loop-helix (bHLH) were significantly upregulated under Fe starvation in shoots. Fe-deficiency-related genotype-dependent and tissue-specific gene expression differences provide new insights into genes involved in iron homeostasis and biofortification genes in wheat.