Plants are among the main sources of micronutrients (i.e. iron, zinc, copper, and manganese) in human diets. Micronutrients are delivered to edible plant tissues via concerted action of transporters mediating mineral uptake, long-distance transport, and loading into edible tissues. While wheat is a globally-important staple crop, its grains are a poor source of micronutrients. Iron Regulated Protein 1 (IRT1) in non-grass species has a broad substrate specificity and in addition to iron, transports zinc, manganese, cobalt and toxic cadmium. Although grasses utilize a different iron uptake strategy, their genomes encode IRT1-like (IRTL1) proteins. Surprisingly, the contribution of IRTL1s to micronutrient transport and accumulation in grains has not been well-studied. We have characterized IRT1-like homoeologs from the three genomes in common wheat, Triticum aestivum (AABBDD) and an orthologue from wheat model, Brachypodium distachyon. We found that TaIRTL1 homoeologs have subfunctionalized in their tissue expression pattern: while all homoeologs were highly expressed in flag leaves, TaIRTL1-A and D were also highly expressed in roots, TaIRTL1-A and B were highly expressed in flowers. BdIRTL1 was preferentially expressed in shoots and was upregulated by iron and copper deficiencies. TaIRTL1 homoeologs and BdIRTL1 differed in their ability to complement iron, zinc, copper and manganese deficiency of yeast micronutrient uptake mutants. Unlike the Arabidopsis irtl1 mutant, the brachypodium irtl1-1 knockout was able to grow without iron supplementation; however, its transition to flowering was delayed, it had altered flower morphology and fertility, decreased pollen production, viability and germination. These defects were, in part, rescued by the excess iron, copper, or manganese. The irtl1-1 mutant has also altered iron, copper, and manganese tissue distribution, which resulted in the reduced accumulation of these minerals in grains. These data increase our understanding of IRTL1 function in grasses and suggest that these transporters can be employed for cereal crops biofortification.
Coauthors: Yana Kavulych – School of Integrative Plant Science – Cornell University; Huajin Sheng – School of Integrative Plant Science – Cornell University; Yonghong Zhou – Professor, Triticeae Research Institute, Sichuan Agriculture University; Olena K. Vatamaniuk – Professor, School of Integrative Plant Science, Cornell University