Journal of Energy Bioscience 2025, Vol.16, No.3, 139-150 http://bioscipublisher.com/index.php/jeb 141 3 Biological Mechanisms of Iron Uptake, Transport, and Storage in Wheat 3.1 Soil-to-root uptake mechanisms: Strategy II (chelation strategy in grasses) Wheat is a grass plant that absorbs iron mainly through the "Strategy II" mechanism. When iron is deficient, wheat roots turn on some special genes that allow the plant to produce more substances called plant siderophores (PS), especially DMA. These PS molecules are secreted into the soil by the roots, where they can grab Fe(III) in the soil and turn it into a complex that the plant can absorb. Genes like NAS and DMAS become particularly active when iron is deficient. They help synthesize and transport these small iron-grabbing molecules, making it easier for wheat to absorb iron from the soil (Wang et al., 2019; Wang et al., 2020). 3.2 Transport systems: Role of YS1/YSL transporters, ZIP family proteins Once iron is absorbed by the roots, it has to rely on the transport system in the body to transport it to other parts, such as leaves and grains. In this process, some special proteins play a key role. YS1 and YSL proteins can transport small molecules linked to iron, such as Fe-NA or Fe-DMA, across the cell membrane. They are particularly important in long-distance transport from roots to leaves and leaves to grains. Proteins of the ZIP family also help iron move back and forth between cells. In addition, proteins such as NRAMP and MFS are also involved in the redistribution of iron to keep the body's iron in balance (Connorton et al., 2017; Wang et al., 2019; Wang et al., 2020). 3.3 Iron storage: Ferritin localization, iron distribution in wheat grain Iron is not randomly distributed in wheat grains, but has a certain location. It is mostly stored in cells in the form of ferritin, especially concentrated in the organelles of the aleurone layer and endosperm. Using some imaging techniques and isotope labeling methods, studies have found that iron is transported along the symplasmic route and finally accumulates in the aleurone layer, endosperm and embryo. If wheat is allowed to express more iron transport proteins like TaVIT2, the iron content in the grain, especially the white flour part, can be increased without increasing anti-nutritional components such as phytate (Connorton et al., 2017; Sheraz et al., 2021). 3.4 Genomic insights: Key genes/QTLs involved in iron homeostasis The mechanism by which wheat regulates iron content is related to many genes and QTLs (quantitative trait loci). When iron is deficient, some genes responsible for absorbing, transporting and storing iron will be "turned on", such as NAS, DMAS, TOM, YSL, NRAMP and bHLH. The transcription factors of the bHLH family are very critical in this process. They regulate the expression of other genes like switches. Now, through QTL analysis and genome-wide association studies (GWAS), many gene loci related to grain iron content have been found. These results also provide new directions and targets for future wheat breeding (Wang et al., 2020; Tanin et al., 2024) (Figure 1). Figure 1 Regulatory pathway of Fe acquisition and trafficking in wheat. The elongated circles indicate the transcription factors. The light brown rounded rectangles indicate signalling proteins. The light blue elongated circle shows genes contributing to Fe acquisition and long-distance transportation (Adopted from Tanin et al., 2024)
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