The main reason for human iron deficiency is that plant seeds, as a major dietary source of iron for humans, are low in iron and high in anti-nutrition factors. Understanding the molecular basis controlling translocation of iron to the seeds are essential for resolving the problem of human iron deficiency, as well as for plant nutrition and agricultural production.
Nicotianamine (NA) is a metal-chelating molecule required for long-distance transport of iron (Fe) in higher plants. It is one of the best enhancer for the bioavailability of iron in human and animals and can help prevent hypertension and Alzheimer's disease. Identification and characterization of the genes controlling translocation of NA and NA-chelated Fe to seeds are critical to improve nutrition of human food. However, these genes and how they function remain unknown.
In a study published in
Science Advances, researchers from CAS Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences uncovered two members of the nitrate/peptide transporter family (NPF) as NA efflux transporters, and named them
NAET1 and
NAET2 (NA Efflux Transporter 1 and 2), respectively.
They found that NAET1 and NAET2 are in charge of unloading of NA from the cells producing them to the vascular system.
Knockout of both NAET genes results in dramatic decreases of NA in the vascular system, and in the sink organs including seeds and flowers. The decrease of NA in the vascular system of the mutant losing the NAET genes further leads to a 75.4% decrease of Fe and a 90.9% decrease of Cu in the seeds. This demonstrated that the NAET genes play a major role in seed iron and copper contents.
Besides, the researchers revealed that the NAET1 and NAET2 proteins are localized within cells to a type of secretory vesicles, which mediates NA efflux from cells. This resembles the release of neurotransmitters from animal synaptic vesicles, which has never been found in plants.
This study addresses a long-sought question in plant nutrition, and has implications for generating crops with enhanced Fe nutrition to resolve the ‘hidden hunger’ problems. The discovery of a transport mechanism in plant resembling neurotransmitter release in animal opens up new avenues for studying molecular and ion transport processes in plant.
