Low-cesium rice: mutation in OsSOS2 reduces radiocesium in rice grains

<jats:title>Abstract</jats:title><jats:p>In Japan, radiocesium contamination in foods has become of great concern and it is a primary issue to reduce grain radiocesium concentration in rice (<jats:italic>Oryza sativa</jats:italic> L.). Here, we report a <jats:italic>low-cesium rice mutant 1</jats:italic> (<jats:italic>lcs1</jats:italic>) with the radiocesium concentration in grain about half that in the wild-type cultivar. Genetic analyses revealed that a mutation in <jats:italic>OsSOS2</jats:italic>, which encodes a serine/threonine-protein kinase required for the salt overly sensitive (SOS) pathway in plants, is responsible for the decreased cesium (Cs) concentrations in <jats:italic>lcs1</jats:italic>. Physiological analyses showed that Cs<jats:sup>+</jats:sup> uptake by <jats:italic>lcs1</jats:italic> roots was significantly decreased under low-potassium (K<jats:sup>+</jats:sup>) conditions in the presence of sodium (Na<jats:sup>+</jats:sup>) (low K<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup>). The transcript levels of several K<jats:sup>+</jats:sup> and Na<jats:sup>+</jats:sup> transporter genes, such as <jats:italic>OsHAK1</jats:italic>, <jats:italic>OsHAK5</jats:italic>, <jats:italic>OsAKT1</jats:italic>, and <jats:italic>OsHKT2;1</jats:italic> were significantly down-regulated in <jats:italic>lcs1</jats:italic> grown at low K<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup>. The decreased Cs<jats:sup>+</jats:sup> uptake in <jats:italic>lcs1</jats:italic> might be closely related to the lower expression of these genes due to the K<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup> imbalance in the <jats:italic>lcs1</jats:italic> roots caused by the <jats:italic>OsSOS2</jats:italic> mutation. Since the <jats:italic>lcs1</jats:italic> plant had no significant negative effects on agronomic traits when grown in radiocesium-contaminated paddy fields, this mutant could be used directly in agriculture for reducing radiocesium in rice grains.</jats:p>