Transcriptome analyses give insights into selenium‐stress responses and selenium tolerance mechanisms in Arabidopsis

Abstract

Selenate is chemically similar to sulfate and can be taken up and assimilated by plants via the same transporters and enzymes. In contrast to many other organisms, selenium (Se) has not been shown to be essential for higher plants. In excess, Se is toxic and restricts development. Both Se deficiency and toxicity pose problems worldwide. To obtain better insights into the effects of Se on plant metabolism and into plant mechanisms involved in Se tolerance, the transcriptome of Arabidopsis plants grown with or without selenate was studied and Se-responsive genes identified. Roots and shoots exhibited different Se-related changes in gene regulation and metabolism. Many genes involved in sulfur (S) uptake and assimilation were upregulated. Accordingly, Se treatment enhanced sulfate levels in plants, but the quantity of organic S metabolites decreased. Transcripts regulating the synthesis and signaling of ethylene and jasmonic acid were also upregulated by Se. Arabidopsis mutants defective in ethylene or jasmonate response pathways exhibited reduced tolerance to Se, suggesting an important role for these two stress hormones in Se tolerance. Selenate upregulated a variety of transcripts that were also reportedly induced by salt and osmotic stress. Selenate appeared to repress plant development, as suggested by the downregulation of genes involved in cell wall synthesis and auxin-regulated proteins. The Se-responsive genes discovered in this study may help create plants that can better tolerate and accumulate Se, which may enhance the effectiveness of Se phytoremediation or serve as Se-fortified food.

Cooperative Ethylene and Jasmonic Acid Signaling Regulates Selenite Resistance in Arabidopsis

“…The above-mentioned studies showed no indication that ethylene plays a role in S deficiency responses. However, a recent comprehensive gene expression analysis showed that transcripts regulating ethylene synthesis (ACS6) and signaling (ERF) were up-regulated by selenate treatment, and plants overexpressing ERF1 exhibited an increase in selenate resistance (Van Hoewyk et al, 2008). These results indicate that Se resistance achieved through ethylene signaling is not mediated by S star- vation resulting from the Se treatment but is a Se-specific response.…”

Dissection of the Control of Anion Homeostasis by Associative Transcriptomics in Brassica napus

“…Ethylene directly induces the activity of the key enzyme of sulfate assimilation, adenosine 59-phosphosulfate reductase (APR), and ethylene signaling is important for the regulation of this enzyme by salt (Koprivova et al, 2008). Arabidopsis mutants in ethylene signaling are more sensitive to selenium, which primarily affects sulfate uptake and assimilation (Van Hoewyk et al, 2008). Ethylene production is affected by nitrate supply, and ethylene signaling is involved in the regulation of nitrate transporters (Zheng et al, 2013), showing a general role of this phytohormone in the control of plant nutrition.…”

New insights into the roles of ethylene and jasmonic acid in the acquisition of selenium resistance in plants

“…Incidentally, an increase in cytosolic calcium concentration is also expected in these plants since many genes related to calcium signaling, such as calcium transporters, calcium binding proteins and calmodulin genes, were identified in the transcriptome analysis of selenate-treated plants. 7 The Se-induced ROS mimic an oxidative burst in plant cells, and the perception of this change triggers a wide array of signaling cascades similar to those induced by plant pathogens. Furthermore, Se-induced changes in the levels of free calcium may phosphorylate one of the subunits of NADPH-oxidase known to generate ROS, or it may directly affect NADPH oxidase activity because this enzyme has an N-terminal sequence with two calcium-binding EF-hand motifs.…”

“…These mutants showed less resistance to selenite and selenate than wildtype plants. 1,7 Conversely, treatment of MeJA or 1-aminocyclopropane-1-carboxylic acid (ACC; precursor of ethylene) enhanced selenite resistance in a Se-sensitive Arabidopsis ecotype, Ws-2. 1 These results further suggest that ethylene and JA are important for Se resistance in plants.…”

“…7 In a transcriptome study performed to identify selenate-responsive genes, the expression of many ethylene and/or jasmonic acid (JA) responsive genes was induced by selenate treatment. Induction of many of these same ethylene and/or JA responsive genes was also observed in selenite-treated plants.…”