The Conservation of VIT1-Dependent Iron Distribution in Seeds

Abstract

One third of people suffer from anemia, with iron (Fe) deficiency being the most common reason. The human diet includes seeds of staple crops, which contain Fe that is poorly bioavailable. One reason for low bioavailability is that these seeds store Fe in cellular compartments that also contain antinutrients, such as phytate. Thus, several studies have focused on decreasing phytate concentrations. In theory, as an alternative approach, Fe reserves might be directed to cellular compartments that are free of phytate, such as plastids. However, it is not known if seed plastid can represent a major Fe storage compartment in nature. To discover distinct types of Fe storage in nature, we investigated metal localizations in the seeds of more than twenty species using histochemical or X-ray based techniques. Results showed that in Rosids, the largest clade of eudicots, Fe reserves were primarily confined to the embryo of the seeds. Furthermore, inside the embryos, Fe accumulated specifically in the endodermal cell layer, a well-known feature that is mediated by VACUOLAR IRON TRANSPORTER1 (VIT1) in model plant Arabidopsis thaliana . In rice, Fe enrichment is lost around the provasculature in the mutants of VIT1 orthologs. Finally, in Carica papaya , Fe accumulated in numerous organelles resembling plastids; however, these organelles accumulated reserve proteins but not ferritin, failing to prove to be plastids. By investigating Fe distribution in distinct plant lineages, this study failed to discover distinct Fe storage patterns that can be useful for biofortification. However, it revealed Fe enrichment is widely conserved in the endodermal cell layer in a VIT1-dependent manner in the plant kingdom.

Structure and function of the vacuolar Ccc1/VIT1 family of iron transporters and its regulation in fungi

“…In the case of Plasmodium parasites, VIT1 plays a major role in iron detoxification during infection and is considered as a potential target for anti-malaria drugs [48] . VIT1 protein sequences within group V share high similarity through the plant kingdom and are responsible for iron accumulation around the provasculature in seeds [49] . However, plant VIT1 homologs have experimented functional divergence.…”

Vacuolar Iron Transporter (Like) proteins: Regulators of cellular iron accumulation in plants

“…However, vacuolar sequestration of Fe represents an important cellular iron homeostasis mechanism in most plants (Ravet et al, 2009). Recently, analysis of accumulation of Fe in seeds in 21 distinct plant lineages revealed that Vacuolar Iron Transporter (VIT) mediated vacuolar Fe accumulation is widely conserved in plant kingdom (Eroglu et al, 2019). Not only in seeds, but recent reports also highlight the important role of VIT and VIT‐Like (VTL) genes in Fe transport during symbiotic nitrogen fixation (SNF) in legumes, which suggest universal role of these transporters in Fe transport and homeostasis within the plant kingdom.…”

Handing off iron to the next generation: how does it get into seeds and what for?

“…In beans (Phaseolus vulgaris), Fe stores also concentrates around vascular tissues 86 . Recently, this observation was extended to Brassicales and even Rosids, which represent a wide group including a third of the angiosperms 87,88 . However, in many cases the number of cell layers that accumulate Fe is increased, to 2, the endodermis and one cortical cell layer in Brassicales, or even more cortical cell layers in other Rosids, compared to endodermis only in Arabidopsis 83,87,88 .…”

“…However, in many cases the number of cell layers that accumulate Fe is increased, to 2, the endodermis and one cortical cell layer in Brassicales, or even more cortical cell layers in other Rosids, compared to endodermis only in Arabidopsis 83,87,88 . While screening representatives of the different groups of angiosperm, interesting exceptions were identified in Chenopodium quinoa and Carica papaya 87,88 . There are certainly more diverse patterns to be discovered.…”