Calcium-permeable cation channels are involved in uranium uptake in Arabidopsis thaliana.

Uranium (U) is a non-essential and toxic element that is taken up by plants from the environment. The assimilation pathway of U is still unknown in plants. In this study, we provide several evidences that U is taken up by the roots of Arabidopsis thaliana through Ca2+-permeable cation channels. First, we showed that deprivation of Arabidopsis plants with calcium induces a 1.5-fold increase in the capacity of roots to accumulate U, suggesting that calcium deficiency promotes the radionuclide import pathway. Second, we showed that external calcium inhibits U accumulation in roots, suggesting a common route for the uptake of both cations. Third, we found that gadolinium, nifedipine and verapamil inhibit the absorption of U, suggesting that different types of Ca2+-permeable channels serve as a route for U uptake. Last, we showed that U bioaccumulation in Arabidopsis mutants deficient for the Ca2+-permeable channels MCA1 and ANN1 is decreased by 40%. This suggests that MCA1 and ANN1 contribute to the absorption of U in different zones and cell layers of the root. Together, our results describe for the first time the involvement of Ca2+-permeable cation channels in the cellular uptake of U.

Development of a metalloproteomic approach to analyse the response of Arabidopsis cells to uranium stress.

Uranium is a naturally occurring radionuclide that is absorbed by plants and interferes with many aspects of their physiology and development. In this study, we used an ionomic, metalloproteomic, and biochemical approach to gain insights into the impact of uranyl ions on the proteome of Arabidopsis thaliana cells. First, we showed that most of the U was trapped in the cell wall and only a small amount of the radionuclide was found in the cell-soluble fraction. Also, the homeostasis of several essential elements was significantly modified in the cells challenged with U. Second, the soluble proteome from Arabidopsis cells was fractionated into 10 subproteomes using anion-exchange chromatography. Proteomic analyses identified 3676 proteins in the different subproteomes and the metal-binding proteins were profiled using inductively coupled plasma mass spectrometry. Uranium was detected in several chromatographic fractions, indicating for the first time that several pools of Arabidopsis proteins are capable of binding the uranyl ion in vivo. Third, we showed that the pattern of some lysine and arginine methylated proteins was modified following exposure to U. We further identified that the ribosomal protein RPS10C was dimethylated at two arginine residues in response to uranyl ion stress. Together, these results provide the first clues for the impact of U on the Arabidopsis proteome and pave the way for the future identification of U-binding proteins.

Protein lysine methylation contributes to modulating the response of sensitive and tolerant Arabidopsis species to cadmium stress.

The mechanisms underlying the response and adaptation of plants to excess of trace elements are not fully described. Here, we analysed the importance of protein lysine methylation for plants to cope with cadmium. We analysed the effect of cadmium on lysine-methylated proteins and protein lysine methyltransferases (KMTs) in two cadmium-sensitive species, Arabidopsis thaliana and A. lyrata, and in three populations of A. halleri with contrasting cadmium accumulation and tolerance traits. We showed that some proteins are differentially methylated at lysine residues in response to Cd and that a few genes coding KMTs are regulated by cadmium. Also, we showed that 9 out of 23 A. thaliana mutants disrupted in KMT genes have a tolerance to cadmium that is significantly different from that of wild-type seedlings. We further characterized two of these mutants, one was knocked out in the calmodulin lysine methyltransferase gene and displayed increased tolerance to cadmium, and the other was interrupted in a KMT gene of unknown function and showed a decreased capacity to cope with cadmium. Together, our results showed that lysine methylation of non-histone proteins is impacted by cadmium and that several methylation events are important for modulating the response of Arabidopsis plants to cadmium stress.