Study of transporters involved in cesium uptake by roots and translocation to the aerial parts in Arabidopsis thaliana

¹³⁴Cs and ¹³⁷Cs, two radioactive isotopes unintentionally released after the Chernobyl and the Fukushima accidents, are of major concern for ecosystems protection and human health. Together with the soil and the soil solution composition, plant properties have a major influence on the amount of caesium uptake which is highly heterogeneous between species. Due to the important role of transporters in the control of elements fluxes, the aim during my thesis was to identify and characterize those that were involved in a significant part of cesium transport. Due to analogy with potassium (K), an essential macronutrient for plants, caesium is supposed to pass predominantly through potassium carriers. Potassium transport involves a diversity of proteins and their respective contribution depends on the level of K supply to the plant. Therefore, I started my project testing the effect of three different K-treatments on uptake, accumulation and distribution of caesium. Concerning the effects of K supply on root uptake of caesium, our results are consistent with the known role of the potassium transporter HAK5 and non-selective cations channels respectively. Additionally, our observations show that two potassium channels from the Shaker family could be involved in caesium translocation and recirculation. The HAK5 transporter mentioned above is already well characterized for its role in the root uptake of caesium and potassium. This transporter belongs to the KUP/HAK/KT family with 12 other proteins in A. thaliana. Results produced during my thesis demonstrate in planta the role of KUP9 transporter - a member of the KUP family-, which has received little attention so far. Changing in potassium uptake has not been observed in mutant lines disrupted in this KUP9 transporter: it could be possible to modulate caesium uptake without alteration of potassium nutrition. This result is very promising for management strategies of contaminated lands modulating plant properties to accumulate large amount of caesium (phytoremediation) or to limit caesium transfer in foodstuffs (safe food). (author)