Abstract
Sulfite reductase (SiR) functions in sulfate assimilation pathway. However, whether it is involved in stress response in crops is largely unknown. Here, the SiR ortholog from Zea mays (ZmSiR) was characterized. The recombinant ZmSiR protein was purified from E. coli. It exhibited sulfite-dependent activity and had strong affinity for sulfite. ZmSiR transcripts were markedly up-regulated by cold and methyl viologen (MV) treatments. Overexpression of ZmSiR complemented growth retardation phenotype of Arabidopsis atsir mutant. ZmSiR-overexpressing Arabidopsis plants were tolerant to severe SO2 stress and rescued the susceptible phenotype of the atsir. ZmSiR knock-down transgenic maize plants with 60% residual transcripts were more susceptible to cold or oxidative stress than wild-type. The severe damage phenotypes of the ZmSiR-compromised maize plants were accompanied by increases of sulfite and H2O2 accumulations, but less amounts of GSH. The qPCR analysis revealed that there was significantly altered expression of several key sulfur metabolism-related genes in ZmSiR-impaired maize lines under cold or MV stress. Particularly, ZmAPR2 expression was significantly elevated, suggesting that toxic sulfite accumulation in ZmSiR-impaired plants could be attributable to the reduced SiR coupled to increased ZmAPR2 expression. Together, our results indicate that ZmSiR is involved in cold and oxidative stress tolerance possibly by modulating sulfite reduction, GSH-dependent H2O2 scavenging, and sulfur-metabolism related gene expression. ZmSiR could be exploited for engineering environmental stress-tolerant varieties in molecular breeding of maize.
Highlights
In higher plants, the assimilatory sulfate reduction is an essential metabolic process in which a great number of sulfur-containing amino acids, sulfolipids and coenzymes are synthesized (Leustek and Saito, 1999; Leustek et al, 2000; Lewandowska and Sirko, 2008)
At the start of this work, total RNAs from 2-week-old maize plants, which had been treated with 20 μM methyl viologen (MV) for 12 h, were used as samples for transcriptome analysis to identify genes responsive to oxidative stress
Amino acid sequence comparisons have revealed that ZmSiR exhibits high identity to counterpart proteins from Arabidopsis thaliana (71% identity), Solanum lycopersicum (65% identity), Ricinus communis (67% identity), Nicotiana benthamiana (66% identity), Glycine max (68% identity), Oryza sativa (91% identity), Brachypodium distachyon (89% identity), Hordeum vulgare (89% identity), and Sorghum bicolor (97% identity) (Supplementary Table S2)
Summary
The assimilatory sulfate reduction is an essential metabolic process in which a great number of sulfur-containing amino acids, sulfolipids and coenzymes are synthesized (Leustek and Saito, 1999; Leustek et al, 2000; Lewandowska and Sirko, 2008). This process involves several successive enzymatic reactions that occur in chloroplasts. The product adenosine-phosphosulfate is reduced to sulfite by APS reductases (APRs). . ZmSiR Confers Oxidative Stress Tolerance reduction of the toxic sulfite to sulfide is catalyzed by sulfite reductase (SiR). The sulfide is further incorporated into cysteine by O-acetyl-serlyases that can be used for synthesizing other sulfur-containing compounds such as glutathione (Nakayama et al, 2000)
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