NARO has, for the first time in the world, discovered that the rice potassium transporter OsHAK1 transports not only an essential nutrient element but also thallium, a toxic element for living organisms. Although OsHAK1 has previously been known to be involved in cesium uptake, this study is the first to reveal a molecular mechanism by which multiple harmful elements are taken up into plants via a single transporter. These findings are expected to contribute to the development of crop varieties that absorb fewer toxic elements and to the production of safer agricultural products in environments at risk of contamination.
Overview
Thallium (Tl) is a heavy metal element known to be toxic to living organisms even at trace levels. Thallium released into the environment through mining activities and industrial wastewater can migrate into agricultural land via soil and water systems, where it may be taken up by crops. In addition, assessing human exposure through food and evaluating associated health risks have become international concerns. Reflecting these global trends, Japan's Ministry of Agriculture, Forestry and Fisheries conducted surveys of thallium levels in brown rice and leafy vegetables during fiscal years 2024-2025, highlighting the need for a deeper scientific understanding of thallium accumulation in crops.
However, the molecular mechanisms by which crops absorb thallium have remained largely unclear. Because thallium shares chemical properties with potassium, an essential nutrient, this study focused on potassium transporters and analyzed the rice transporter OsHAK1, which is also known as a cesium transporter. The results demonstrated for the first time that OsHAK1 transports thallium and serves as a major pathway for thallium uptake in rice.
These findings reveal a common molecular mechanism by which multiple non-essential elements, such as thallium and cesium, are taken up into plants via potassium transporters. This work is expected to support the development of crops with reduced uptake of harmful elements through functional modification and regulation of OsHAK1, ultimately contributing to improved safety for both human health and plant production.
The results of this study were published in the scientific journal Plant and Cell Physiology on February 24, 2026.
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