Abstrakt

The International Debate on Cesium is a Specific Inhibitor of the Akt1-Kc1 Complex-Mediated Potassium Influx in Arabidopsis

Ryoung Shin

 Cesium (Cs+) exists in nature at relatively low levels but occasionally accidental anthropogenic activities spread high levels of Cs+ (most commonly radioactive) which contaminate the environment and enter the food chain. Cs+ disrupts plant growth at high concentrations through pleiotropic effects and the part of the Cs+ toxicity in plants is known to derive from competition and interference with potassium (K+) due to the similarity in physicochemical properties between K+ and Cs+. K+ is an essential nutrient, a lack of which causes serious growth retardation and physiological defects. In order to find the means to sustain plant growth in Cs+-contaminated areas for phytoremediation purpose, the molecular mechanisms of how Cs+ exerts its deleterious effects on K+ accumulation in plants need to be elucidated. In Arabidopsis thaliana, K+ uptake through the roots is considered to be mediated mainly by two players: Arabidopsis K+ Transporter 1 (AKT1) and High Affinity K+ Transporter 5 (HAK5). Expression of HAK5 is swiftly induced in response to K+ deficiency while AKT1 is more responsible for low-affinity K+ uptake. AKT1 forms a tetrameric complex with K+ Rectifying Channel 1 (KC1) to exert proper function. Here, we show that mutation on a member of the major K+ channel AKT1-KC1 complex renders Arabidopsis thaliana hypersensitive to Cs+. Electrophysiological analysis demonstrated that Cs+, but not sodium, rubidium or ammonium, specifically inhibited K+ influx through the AKT1-KC1 complex. In addition, a lack of KC1 further led to an inability of Arabidopsis to accumulate K+ in the plant body due to uncontrollable K+ leakage through the homomeric AKT1 channel. These data indicate that Cs+ is a specific inhibitor of the AKT1 complex-mediated K+ influx and KC1 is essential to avoid K+ leakage. Recent Publications 1. Takiguchi H, Hong J P, Nishiyama H, Hakata M, Nakamura H, Ichikawa H, Park C J and Shin R (2017) Discovery of E3 ubiquitin ligases that alter responses to nitrogen deficiency using rice full-length cDNA OvereXpressor (FOX)-hunting system. Plant Molecular Biology Reporter 35(3):343-354. 2. Adams E, Miyazaki T, Hayaishi-Satoh A, Han M, Kusano M, Khandelia H, Saito K and Shin R (2017) A novel role of methyl cysteinate and cysteine in cesium accumulation and response in Arabidopsis thaliana. Scientific Reports 7:43170. 3. Hong J P, Adams E, Yanagawa Y, Matsui M and Shin R (2017) AtSKIP18 and AtSKIP31, F-box subunits of the SCF E3 ubiquitin ligase complex, mediate the degradation of 14-3-3 proteins in Arabidopsis. Biochemical and Biophysical Research Communications 485(1):174-180. 4. Adams E, Chanban V, Khandelia H and Shin R (2015) Selective chemical binding enhances cesium tolerance in plants through inhibition of cesium uptake. Scientific Reports 5:8842.