Radiocesium, accumulated in the soil by nuclear accidents is a major environmental concern. The transport process of cesium (Cs + ) is tightly linked to the indispensable plant nutrient potassium (K + ) as they both belong to the group I alkali metal with similar chemical properties. Most of the transporters that had been characterized to date as Cs + transporters are directly or indirectly linked to K + . Using a combinatorial approach of physiology, genetics, cell biology and root uptake assay, here we identified two ATP-Binding Cassette (ABC) proteins, ABCG37 and ABCG33 as facilitators of Cs + influx. The gain-of-function mutant of ABCG37 ( abcg37-1 ) showed hypersensitive response to Cs + -induced root growth inhibition, while the double knock out mutant of ABCG33 and ABCG37 ( abcg33-1abcg37-2 ) showed resistance. Single loss-of-function mutant of ABCG33 and ABCG37 did not show any alteration in Cs + response. Short term uptake experiment with radioactive Cs + revealed reduced Cs + uptake in abcg33-1abgc37-2 compared with wild type in presence or absence of K + . Potassium response and content were unaffected in the double mutant background confirming that Cs + uptake by ABCG33 and ABCG37 is independent of K + . Collectively, this work identified two ABC proteins as new Cs + influx carriers, which act redundantly and independent of K + uptake pathway.
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Ashraf et al. (2019) studied this question.