Understanding how plants distribute iron to young leaves

Iron (Fe) is an essential micronutrient for the healthy growth of plants, including many staple crops like rice. Its deficiency remains a common agricultural problem that slashes crop yields, as it leads to impaired photosynthesis, respiration, and nitrogen metabolism. Thus, establishing mechanisms to ensure crops can efficiently take up and utilize Fe, especially in alkaline soils, is a high-stakes challenge for global food security.

Getting Fe into the roots is only the first step; the mineral must then be properly distributed throughout the plant, especially to its young leaves, developing grains, and other active growth tissues. This process is facilitated by the plant’s nodes, which function as central traffic hubs for minerals thanks to their specialized vasculature. More specifically, nodes must carefully partition Fe between the enlarged vascular bundles (EVB), which supply older parts of the plant, and the diffuse vascular bundles (DVB), which transport nutrients to newer tissues. Despite many studies on these processes, the iron transporter protein in charge of releasing Fe into the DVB remained a mystery—until now.

In a recent study, a research team from Okayama University, Japan, led by Professor Jian Feng Ma successfully identified this missing link. Their paper, which was published online in Nature Communications on November 11, 2025 and co-authored by Sheng Huang and Naoki Yamaji, details the function of a newly characterized protein called OsIET1 (Oryza sativa Iron Efflux Transporter 1).

The researchers focused on the OsIET1 gene after previous gene expression profiling indicated its high expression in the nodes. Using various molecular and cellular analytical techniques, the team first determined that OsIET1 encodes a protein that is localized to the plasma membrane, unlike its closely related homologs. Through functional assays, the team then demonstrated that OsIET1 acts as an efflux transporter for ferrous iron, meaning that it actively pumps Fe out of the cell. Its expression was found to be specific to the xylem region of the DVB, where Fe needs to be reloaded for distribution to developing tissues.

To confirm its biological role, the researchers generated knockout rice lines in which the OsIET1 gene was inactivated. These mutant plants exhibited clear signs of iron misdistribution, with Fe levels significantly reduced in young leaves and grains but markedly accumulated in the nodes and older leaves. At the vegetative stage, this caused new leaves to develop a form of yellowing known as chlorosis. At the reproductive stage, the mutant plants exhibited growth problems and, most importantly, showed a staggering decrease in grain yield.

Overall, the identification of OsIET1 fills an important knowledge gap by completing the picture of how rice manages and prioritizes the delivery of Fe. “Given the pivotal role of nodes in mineral distribution, our results reveal OsIET1 mediates inter-vascular Fe transfer, ensuring preferential Fe delivery to developing tissues and thereby promoting optimal plant growth and productivity,” remarks Prof. Ma.

This research has interesting implications for crop management and development. OsIET1 now represents a valuable molecular target for breeding programs and genetic engineering efforts. By manipulating or optimizing this transporter, scientists could potentially enhance Fe distribution within rice plants, leading to crops that are more resilient to Fe-deficient soils. Notably, this work also opens new avenues for exploration into Fe transporters. “The other homologs of OsIET1 remain uncharacterized. Investigation of the subcellular localization of these homologs may provide further insights into the different roles of this clade in Fe transport in the future,” concludes Prof. Ma, suggesting that more discoveries in plants’ mineral transport are yet to come.

About Okayama University, Japan

As one of the leading universities in Japan, Okayama University aims to create and establish a new paradigm for the sustainable development of the world. Okayama University offers a wide range of academic fields, which become the basis of the integrated graduate schools. This not only allows us to conduct the most advanced and up-to-date research, but also provides an enriching educational experience.

Website: https://www.okayama-u.ac.jp/index_e.html

About Professor Jian Feng Ma from Okayama University, Japan

Jian Feng Ma received his Ph.D. in plant nutrition from Kyoto University, Japan in 1991. He joined Okayama University in 1995, where he currently serves as Full Professor at the Institute of Plant Science and Resources. His recent work mainly focuses on identifying transporters for mineral elements including essential, beneficial, and toxic elements in plants, especially in rice, as well as tolerance mechanisms. His group has published over 330 papers in prestigious international journals such as Nature, Nature Plants, Nature Food, and Nature Communications. He has been selected as a Highly Cited Researcher by Clarivate Analytics for 11 consecutive years.