Influence of Sulfur on Transcription of Genes Involved in Arsenic Accumulation in Rice Grains

Abstract

Arsenic (As) contamination of rice grains affects millions of people worldwide. In this study, we found that sulfur application (20As+120S) decreased As concentration in rice grains by 44 % compared to grains without sulfur application (20As+0S). Importantly, sulfur application decreased arsenate [As(V)] and arsenite [As(III)] concentration in rice grains significantly, while there was no significant effect on dimethylarsenate (DMA) concentration. To elucidate the molecular basis of As accumulation in rice grains, we performed Illumina sequencing to acquire the differentially expressed genes induced by arsenate and sulfur treatments. By contrast with the control, the expression of 1,000 genes was found to be changed significantly, with 46 genes upregulated and 954 genes down-regulated in grains grown in arsenate-contaminated soil (20As+0S). Between samples of control and arsenate together with sulfur treatment (20As+ 120S), 1,169 genes expressed significantly differently, with 16 genes up-regulated and 1,153 genes down-regulated. Sulfur application significantly changed the expression of genes involved in As metabolism in rice grains, significantly downregulated phosphate transporter gene OsPT23 and aquaporin gene OsTIP4;2, while ABC transporter genes (OsABCG5, OsABCI7_2 and OsABC6) and phytochelatin synthase genes (OsPCS1, OsPCS3 and OsPCS13) were up-regulated. These results provide an insight into the molecular basis of how sulfur assimilation regulates As accumulation in rice grains.

The Journey of Arsenic from Soil to Grain in Rice

“…There are several reports on decreased As concentrations in shoots at high doses of S that was attributable either to S induced formation of iron plaque or to increased complexation of As in roots ( Hu et al, 2007 ; Zhang et al, 2011 ; Dixit et al, 2015 ). Recently, high S supply mediated decline in As concentration has also been reported in rice grain (44%) in comparison to no S (0 S) supplied plants ( Zhang et al, 2016 ). The high sulfur supply was found to regulate the expression of genes involved in As metabolism viz., down-regulation of the phosphate transporter (PT): OsPT23 and aquaporin gene: OsTIP4;2 (Tonoplast Intrinsic Protein), while upregulation of ABC transporter genes (OsABCG5, OsABCI7_2and OsABC6) and phytochelatin synthase genes (OsPCS1, OsPCS3 and OsPCS13) ( Zhang et al, 2016 ; Figure 4 ).…”

“…Recently, high S supply mediated decline in As concentration has also been reported in rice grain (44%) in comparison to no S (0 S) supplied plants ( Zhang et al, 2016 ). The high sulfur supply was found to regulate the expression of genes involved in As metabolism viz., down-regulation of the phosphate transporter (PT): OsPT23 and aquaporin gene: OsTIP4;2 (Tonoplast Intrinsic Protein), while upregulation of ABC transporter genes (OsABCG5, OsABCI7_2and OsABC6) and phytochelatin synthase genes (OsPCS1, OsPCS3 and OsPCS13) ( Zhang et al, 2016 ; Figure 4 ). It suggests that high sulfur supply allowed plants to synthesize more PCs and sequestrate As to vacuoles efficiently by complexation with PCs via upregulation of PCS and ABC transporter genes.…”

Importance of Mineral Nutrition for Mitigating Aluminum Toxicity in Plants on Acidic Soils: Current Status and Opportunities

“…Generally, high doses of S are recommended to abate arsenic (As) uptake in plants. For example, S treatment (120 mg S·kg −1 soil; Na 2 S 2 O 3 ·5H 2 O) was applied to As (20 mg As·kg −1 soil; Na 2 HAsO 4 ·12H 2 O) contaminated soil, and it was found that As concentrations reduced in rice grains by 44% compared to grains from the treatment without S application [ 175 ]. Recently, S addition (0.5 mM S; MgSO 4 and/or 0.5 mM Na 2 SO 4 ) was shown to be alleviated Al toxicity by increasing minerals (P, Mg and Ca) and relative water contents; decreasing Al and H 2 O 2 contents, and involving S-metabolism and antioxidant enzymes in citrus [ 116 ].…”

Biochemical pathways of arsenic uptake from the environment to human cells

“…The expression of this protein in rice is not high, but independent on the presence of arsenic in the environment. The increase of Si concentration in soil inhibits accumulation of As in (III) [78] and application of sulfur fertilizers counteracts contamination of grain by decreasing As in (III) and As in (V) concentration in rice seeds as well [91,92].…”