Evolutionary Aspects of Selenium Binding Protein (SBP).

Selenium-binding proteins represent a ubiquitous protein family and recently SBP1 was described as a new stress response regulator in plants. SBP1 has been characterized as a methanethiol oxidase, however its exact role remains unclear. Moreover, in mammals, it is involved in the regulation of anti-carcinogenic growth and progression as well as reduction/oxidation modulation and detoxification. In this work, we delineate the functional potential of certain motifs of SBP in the context of evolutionary relationships. The phylogenetic profiling approach revealed the absence of SBP in the fungi phylum as well as in most non eukaryotic organisms. The phylogenetic tree also indicates the differentiation and evolution of characteristic SBP motifs. Main evolutionary events concern the CSSC motif for which Acidobacteria, Fungi and Archaea carry modifications. Moreover, the CC motif is harbored by some bacteria and remains conserved in Plants, while modified to CxxC in Animals. Thus, the characteristic sequence motifs of SBPs mainly appeared in Archaea and Bacteria and retained in Animals and Plants. Our results demonstrate the emergence of SBP from bacteria and most likely as a methanethiol oxidase.

Investigation of the interaction of DAD1-LIKE LIPASE 3 (DALL3) with Selenium Binding Protein 1 (SBP1) in Arabidopsis thaliana.

Phospholipase PLA1-Iγ2 or otherwise DAD1-LIKE LIPASE 3 (DALL3) is a member of class I phospholipases and has a role in JA biosynthesis. AtDALL3 was previously identified in a yeast two-hybrid screening as an interacting protein of the Arabidopsis Selenium Binding Protein 1 (SBP1). In this work, we have studied AtDALL3 as an interacting partner of the Arabidopsis Selenium Binding Protein 1 (SBP1). Phylogenetic analysis showed that DALL3 appears in the PLA1-Igamma1, 2 group, paired with PLA1-Igammma1. The highest level of expression of AtDALL3 was observed in 10-day-old roots and in flowers, while constitutive levels were maintained in seedlings, cotyledons, shoots and leaves. In response to abiotic stress, DALL3 was shown to participate in the network of genes regulated by cadmium, selenite and selenate compounds. DALL3 promoter driven GUS assays revealed that the expression patterns defined were overlapping with the patterns reported for AtSBP1 gene, indicating that DALL3 and SBP1 transcripts co-localize. Furthermore, quantitative GUS assays showed that these compounds elicited changes in activity in specific cells files, indicating the differential response of DALL3 promoter. GFP::DALL3 studies by confocal microscopy demonstrated the localization of DALL3 in the plastids of the root apex, the plastids of the central root and the apex of emerging lateral root primordia. Additionally, we confirmed by yeast two hybrid assays the physical interaction of DALL3 with SBP1 and defined a minimal SBP1 fragment that DALL3 binds to. Finally, by employing bimolecular fluorescent complementation we demonstrated the in planta interaction of the two proteins.

Novel interactions of Selenium Binding Protein family with the PICOT containing proteins AtGRXS14 and AtGRXS16 in Arabidopsis thaliana.

During abiotic stress the primary symptom of phytotoxicity can be ROS production which is strictly regulated by ROS scavenging pathways involving enzymatic and non-enzymatic antioxidants. Furthermore, ROS are well-described secondary messengers of cellular processes, while during the course of evolution, plants have accomplished high degree of control over ROS and used them as signalling molecules. Glutaredoxins (GRXs) are small and ubiquitous glutathione (GSH) -or thioredoxin reductase (TR)-dependent oxidoreductases belonging to the thioredoxin (TRX) superfamily which are conserved in most eukaryotes and prokaryotes. In Arabidopsis thaliana GRXs are subdivided into four classes playing a central role in oxidative stress responses and physiological functions. In this work, we describe a novel interaction of AtGRXS14 with the Selenium Binding Protein 1 (AtSBP1), a protein proposed to be integrated in a regulatory network that senses alterations in cellular redox state and acts towards its restoration. We further show that SBP protein family interacts with AtGRXS16 that also contains a PICOT domain, like AtGRXS14.

Promoter analysis and functional implications of the selenium binding protein (SBP) gene family in Arabidopsis thaliana.

Selenium Βinding Protein (SBP, originally termed SBP56) was identified in mouse liver as a cytosolic protein that could bind radioactive selenium. SBPs are highly conserved proteins present in a wide array of species across all kingdoms and are likely to be involved in selenium metabolism. In Arabidopsis, the selenium binding protein (SBP) gene family comprises three genes (AtSBP1, AtSBP2 and AtSBP3). AtSBP1 and AtSBP2 are clustered in a head-to-tail arrangement on chromosome IV, while AtSBP3 is located on chromosome III. In this work, we studied the promoter activity of the Arabidopsis SBP genes, determined their tissue specificity and showed that they are differentially regulated by sodium selenite and sodium selenate. All three SBP genes are upregulated in response to externally applied selenium compounds and the antioxidant NAC selectively downregulates SBP2. Although the effect on SBP2 levels was the most prominent, in all cases, the concurrent exposure of plants to selenite and the antioxidant supressed the expression of the SBP genes. We provide evidence that (at least) SBP1 expression is tightly linked to detoxification processes related to oxidative stress, since it is downregulated in the presence of NAC in selenium-treated plants. Furthermore, our results suggest that SBP genes may participate in the mechanisms that sense redox imbalance.