Caesium accumulation in yeast and plants is selectively repressed by loss of the SNARE Sec22p/SEC22

The non-essential cation caesium (Cs + ) is assimilated by all organisms. Thus, anthropogenically released radiocaesium is of concern to agriculture. Cs + accumulates owing to its chemical similarity to the potassium ion (K + ). The apparent lack of a Cs + -specific uptake mechanism has obstructed attempts to manipulate Cs + accumulation without causing pleiotropic effects. Here we show that the SNARE protein Sec22p/SEC22 specifically impacts Cs + accumulation in yeast and in plants. Loss of Saccharomyces cerevisiae Sec22p does not affect K + homeostasis, yet halves Cs + concentration compared with the wild type. Mathematical modelling of the uptake time course predicts a compromised vacuolar Cs + deposition in sec22Δ . Biochemical fractionation confirms this and indicates a new feature of Sec22p in enhancing non-selective cation deposition. A developmentally controlled loss-of-function mutant of the orthologous Arabidopsis thaliana SEC22 phenocopies the reduced Cs + uptake without affecting plant growth. This finding provides a new strategy to reduce radiocaesium entry into the food chain. The active uptake of radiocaesium by plants via potassium transport systems results in contamination of food supplies. Here, the authors show that loss of the v-SNARE protein Sec22p/SEC22 specifically reduces the accumulation of Cs + in yeast and plants by repressing its deposition to vacuoles.