Insights into a key sulfite scavenger enzyme sulfite oxidase (SOX) gene in plants

Abstract

Sulfite oxidase (SOX) is a crucial molybdenum cofactor-containing enzyme in plants that re-oxidizes the sulfite back to sulfate in sulfite assimilation pathway. However, studies of this crucial enzyme are quite limited hence this work was attempted to understand the SOXs in four plant species namely, Arabidopsis thaliana, Solanum lycopersicum, Populus trichocarpa and Brachypodium distachyon. Herein studied SOX enzyme was characterized with both oxidoreductase molybdopterin binding and Moco oxidoreductase dimerization domains. The alignment and motif analyses revealed the highly conserved primary structure of SOXs. The phylogeny constructed with additional species demonstrated a clear divergence of monocots, dicots and lower plants. In addition, to further understand the phylogenetic relationship and make a functional inference, a structure-based phylogeny was constructed using normalized RMSD values in five superposed models from four modelled plant SOXs herein and one previously characterized chicken SOX structure. The plant and animal SOXs showed a clear divergence and also implicated their functional divergences. Based on tree topology, monocot B. distachyon appeared to be diverged from other dicots, pointing out a possible monocot-dicot split. The expression patterns of sulfite scavengers including SOX were differentially modulated under cold, heat, salt and high light stresses. Particularly, they tend to be upregulated under high light and heat while being downregulated under cold and salt stresses. The presence of cisregulatory motifs associated with different stresses in upstream regions of SOX genes was thus justified. The protein-protein interaction network of AtSOX and network enrichment with gene ontology (GO) terms showed that most predicted proteins, including sulfite reductase, ATP sulfurylases and APS reductases were among prime enzymes involved in sulfite pathway. Finally, SOX-sulfite docked structures indicated that arginine residues particularly Arg374 is crucial for SOX-sulfite binding and additional two other residues such as Arg51 and Arg103 may be important for SOX-sulfite bindings in plants.

Overexpression of the Maize Sulfite Oxidase Increases Sulfate and GSH Levels and Enhances Drought Tolerance in Transgenic Tobacco

“…Interestingly, it has been reported that Hibiscus chlorotic ringspot virus infection up-regulates plant SO and other S metabolism-related gene transcripts, and increases sulfate and GSH levels for enhanced pathogen defense in kenaf ( Zhang and Wong, 2009 ; Gao et al, 2012 ). Most recently, Filiz et al (2017) investigated expression patterns of sulfite scavengers including SO in 10 natural Arabidopsis ecotypes and found that transcript levels of SO were up-regulated under heat and high light stresses ( Filiz et al, 2017 ). This result, in combination with our current evidence, further reinforces the view that SO may play an important role in abiotic and biotic stress tolerance by accelerating transformation of sulfite to sulfate, thereby contributing to enhanced biosynthesis of S-containing defense compounds such as GSH in plants.…”

“…As a molybdenum-containing enzyme, sulfite oxidase (SO) participates in sulfite metabolism by catalyzing oxidation of toxic sulfite to sulfate ( Kappler and Enemark, 2015 ; Filiz et al, 2017 ). Over the past several decades, studies on plant SO have been centered on its biochemical properties in Arabidopsis ( Eilers et al, 2001 ; Schrader et al, 2003 ; Hansch et al, 2006 ; Byrne et al, 2009 ).…”

“…In recent years, increasing studies have focused on physiological roles of SO in higher plants. Studies on SO from Arabidopsis , tobacco, and tomato have shown that plant SO detoxifies excess sulfite for maintaining sulfite homeostasis by catalyzing the oxidation of sulfite to sulfate in plants ( Brychkova et al, 2007 , 2013 ; Lang et al, 2007 ; Xia et al, 2012a ; Filiz et al, 2017 ). Interestingly, co-regulation of SO and adenosine 5-phosphosulfate reductase (APR) controls sulfate assimilation pathway and stabilizes S distribution by a sulfate-sulfite cycle in Arabidopsis ( Randewig et al, 2012 ).…”

A cotton mitochondrial alternative electron transporter, GhD2HGDH, induces early flowering by modulating GA and photoperiodic pathways

“…A variety of important oligopeptides are synthesized using sulfur‐containing compounds such as glutathione (GSH), phytochelatins, prosthetic groups, vitamins, and cofactors (including biotin, molybdenum cofactor, thiamine, coenzyme A, and S‐adenosyl methionine), as well as secondary metabolites and lipids (Saito, 2000). In plants, sulfite oxidase (SOX) is an essential enzyme that contains molybdenum cofactor and is responsible for reoxidizing sulfite back to sulfate in the sulfite absorption pathway (Filiz et al, 2017). As SOX is a molybdenum cofactor‐binding enzyme (Eilers et al, 2001), plays pivotal roles in energy metabolism, glutathione metabolism, and sulfur metabolism pathways (Xia et al, 2018), their functional characterization in cotton needs further investigation.…”

Proteomic and ecophysiological responses of soybean (Glycine max L.) root nodules to Pb and hg stress

“…Sulfite oxidase (SOX) is an important enzyme of sulfur assimilation pathway which catalyses re-oxidation of sulfite to sulfate. SOX gene in Arabidopsis was differentially expressed under various abiotc stress conditions [ 70 ]. Abundance of SOX expression was found to be upregulated by Pb and downregulated by Hg stress in root nodules of soybean.…”