Plant selenium toxicity: Proteome in the crosshairs.

The metalloid element, selenium (Se) is in many ways special and perhaps because of this its research in human and plant systems is of great interest. Despite its non-essentiality, higher plants take it up and metabolize it via sulfur pathways, but higher amounts of Se cause toxic symptoms in plants. However, the molecular mechanisms of selenium phytotoxicity have been only partly revealed; the data obtained so far point out that Se toxicity targets the plant proteome. Besides seleno- and oxyproteins, nitroproteins are also formed due to Se stress. In order to minimize proteomic damages induced by Se, certain plants are able to redirect selenocysteine away from protein synthesis thus preventing Se-protein formation. Additionally, the damaged or malformed selenoproteins, oxyproteins and nitroproteins may be removed by proteasomes. Based on the literature this review sets Se toxicity mechanisms into a new concept and it draws attention to the importance of Se-induced protein-level changes.