Influence of sulfate supply on selenium uptake dynamics and expression of sulfate/selenate transporters in selenium hyperaccumulator and nonhyperaccumulator Brassicaceae

Abstract

SummaryStanleya pinnata not only hyperaccumulates selenium (Se) to 0.5% of its dry weight, but also exhibits higher tissue Se-to-sulfur (S) ratios than other species and its surroundings.To investigate the mechanisms underlying this Se enrichment, we compared S. pinnata with the nonhyperaccumulators S. elata and Brassica juncea for selenate uptake in long-(9 d) and short-term (1 h) assays, using different concentrations of selenate and competitor sulfate. Different sulfate pre-treatments (0, 0.5, 5 mM, 3 d) were also tested for effects on selenate uptake and sulfate transporters' expression.Relative to nonhyperaccumulators, S. pinnata showed higher rates of root and shoot Se accumulation and less competitive inhibition by sulfate or by high-S pretreatment. The selenate uptake rate for S. pinnata (1 h) was three-to four-fold higher than for nonhyperaccumulators, and not significantly affected by 100-fold excess sulfate, which reduced selenate uptake by 100% in S. elata and 40% in B. juncea. Real-time reverse transcription PCR indicated constitutive upregulation in S. pinnata of sulfate transporters SULTR1;2 (root influx) and SULTR2;1 (translocation), but reduced SULTR1;1 expression (root influx).In S. pinnata, selenate uptake and translocation rates are constitutively elevated and relatively sulfate-independent. Underlying mechanisms likely include overexpression of SULTR1;2 and SULTR2;1, which may additionally have evolved enhanced specificity for selenate over sulfate.

Quick selenium accumulation in selenium-rich rice and its physiological changes in selenium environment

“…As the previous work reported, sulphur replete Arabidopsis mutants sultr1;2, lacking SULTR1;2 but not those lacking other sulphate transporters, take up less selenate and exhibit greater tolerance to selenium in the rhizosphere than wild-type plants [19,20], and the expression of genes encoding SULTR1;2 generally increases in plant when tissue Se concentrations rise [5], which is in accordance with our result. Similarly, the expression of OsPT2 increases in roots of plants lacking sufficient phosphorus and results in a greater capacity for selenite uptake [37], and rice mutants lacking OsPT2 take up significantly less selenite than wild-type plants [18].…”

“…What's more, selenite and phosphate (Pi) share similar uptake mechanisms, so Pi transporters, such as rice OsPT2, catalyze the uptake of selenite [18]. In Arabidopsis thaliana and Stanleya pinnata, sulfate transporter SULTR1;2 plays a central and specific role in selenate sensitivity [5,19,20]. In addition, cadmium (Cd) has antagonistic effects on selenium, as disclosed by previous work [21].…”

“…Selenium resists cellular senescence and death by resisting peroxides and scavenging free radicals, thereby reducing or delaying the formation of lipofuscin [4]. However, its essentiality for plants has not yet been established [5]. Although the human demand for Se is not high, the abundance of Se is very low in the Earth's crust.…”

“…At present, the research on selenization of rice mainly focuses on two aspects: one is to improve the selenium content in rice by applying exogenous sodium selenate from the perspective of physiological cultivation; the other is to breed selenium-rich parents according to the genetic differences among varieties [1,5,14,15]. Studies have shown that genotype essentially determines the difference in Se uptake and enrichment in rice [16].…”

Quick selenium accumulation in the selenium-rich rice and its physiological responses in changing selenium environments

“…The presenting result (Fig. 4c) is in accordance with the previous study that the expression of SULTR1;2was promoted by the application of Sein Arabidopsis [12], providing evidence that SULTR1;2 acts as a conserved factor in mediating the assimilation of Se among plant species. In rice, the overexpression of OsPT2 was able to increase the uptake of Se [37], while the capacity was greatly compromised in the Ospt2 mutant [19].…”