Identification of soybean mutants with low cesium accumulation, characterization of the causative gene, and field evaluation

The radiocesium contamination of food poses a serious threat to food safety because radiocesium has a long half-life and emits harmful radiation during decay. Therefore, it is important to reduce radiocesium uptake by crops. In this study, we identified low-cesium-accumulating soybean mutants from an ethyl methanesulfonate-induced mutant population. Through the phenotypic screening of the population based on the seed cesium concentration, 10 candidate low-cesium-accumulating mutant lines were selected. Five of these exhibited significantly reduced seed radiocesium concentrations compared with the original variety, and one had accumulated an excessive amount of sodium. Since plant intracellular sodium ion homeostasis is regulated by the salt overly sensitive (SOS) pathway, sequence analysis of GmSOS1, which encodes an Na+/H+ antiporter in this pathway, revealed that the high-sodium-accumulating line contains a mutation in this gene. Additionally, two more gmsos1 mutant lines were isolated from the mutant population. In the field trial, the three independent gmsos1 mutant lines possessed lower seed cesium concentrations than the wild type. These results indicate that GmSOS1 is responsible for seed cesium accumulation, and gmsos1 mutants are potential breeding materials for reducing hazardous radiocesium accumulation in soybeans.