Desulfoglucosinolate Sulfotransferases from Arabidopsis thaliana Catalyze the Final Step in the Biosynthesis of the Glucosinolate Core Structure

Abstract

The phytotoxin coronatine is a structural analog of octadecanoid signaling molecules, which are well known mediators of plant defense reactions. To isolate novel coronatine-regulated genes from Arabidopsis thaliana, differential mRNA display was performed. Transcript levels of CORI-7 (coronatine induced-7) were rapidly and transiently increased in coronatine-treated plants, and the corresponding cDNA was found to encode the sulfotransferase AtST5a. Likewise, upon wounding, an immediate and transient increase in AtST5a mRNA levels could be observed in both locally wounded and unwounded (systemic) leaves. Furthermore, application of octadecanoids and ethylene as compounds involved in plant wound defense reactions resulted in AtST5a gene activation, whereas pathogen defense-related signals (yeast elicitor and salicylic acid) were inactive. AtST5a and its close homologs AtST5b and AtST5c were purified as His 6 -tagged proteins from Escherichia coli. The three enzymes were shown to catalyze the final step in the biosynthesis of the glucosinolate (GS) core structure, the sulfation of desulfoglucosinolates (dsGSs). They accept a broad range of dsGSs as substrates. However, in a competitive situation, AtST5a clearly prefers tryptophan-and phenylalanine-derived dsGSs, whereas long chain dsGSs derived from methionine are the preferred substrates of AtST5b and AtST5c. Treatment of Arabidopsis plants with low concentrations of coronatine resulted in an increase in the amounts of specific GSs, primarily glucobrassicin and neoglucobrassicin. Hence, it is suggested that AtST5a is the sulfotransferase responsible for the biosynthesis of tryptophan-derived GSs in vivo.Compared with the animal cell, very little is known regarding the structural and regulatory roles of the sulfate group in plants. The transfer of the active sulfate group from 3Ј-phosphoadenosine 5Ј-phosphosulfate (PAPS) 1 to acceptor molecules is catalyzed by sulfotransferases. Members of the superfamily of sulfotransferases are known in prokaryotes as well as eukaryotes; however, the study of enzymes that catalyze the sulfation reaction in plants considerably lags behind that in animal systems. Cytosolic sulfotransferases from plants have been characterized in some detail (Ref. 1 and references therein), and some cDNAs have been identified. These fall into three subgroups: the flavonol sulfotransferases described for Flaveria species (1), the steroid sulfotransferases identified in Brassica napus (2, 3), and a hydroxyjasmonic acid-specific sulfotransferase from Arabidopsis thaliana (4). An additional sulfotransferase (RaR047, At2g03760) has been cloned from A. thaliana, and its mRNA level was found to be up-regulated by pathogens and salicylic acid; however, its physiological substrate is still unknown (5).In plants, sulfate groups occur in a number of secondary metabolites, notably the sulfoflavonoids (6) and the glucosinolates (7). Glucosinolates (GSs) are secondary compounds found in at least 16 different plant families, 15 of which belong to the order Cappa...

A robust omics-based approach for the identification of glucosinolate biosynthetic genes

“…To date, some of these candidate genes have been characterized experimentally. The predicted functions of the AtSOTs and UGT74B1 have been confirmed by concurrent studies Piotrowski et al 2004;Douglas Grubb et al 2004).…”

“…SUR1 and UGT74B1, the genes involved in both Met-and Trp-derived GSL biosynthesis (Mikkelsen et al 2004;Douglas Grubb et al 2004), are in the boundary region of two modules. It has been reported that the preferable substrates of the AtSOT17 product are Met-and Phe-derived GSLs (Klein et al 2006;Piotrowski et al 2004). Although graph structure depends on the dataset and the measure of similarity used, it may possibly suggest the functional relationship of the genes.…”

Elucidation of Gene-to-Gene and Metabolite-to-Gene Networks inArabidopsis by Integration of Metabolomics andTranscriptomics

“…These results confirmed that the three sulfotransferase-like genes, which clustered with known GLS biosynthesis genes after BL-SOM analysis, actually encode the proteins catalyzing PAPS-dependent sulfation of desulfo-GLSs to GLSs. During the reviewing process of this publication, Piotrowski et al (23) reached the same conclusion by quite different strategy to ours and reported that these three genes encode desulfo-GLS sulfotransferase. It was also the case with At1g24100, which was assumed to encode S-glucosyltransferase involved in GLS biosynthesis (24).…”

The Plastidic Bile Acid Transporter 5 Is Required for the Biosynthesis of Methionine-Derived Glucosinolates inArabidopsis thaliana

“…A second oxidation step leads to an aci-nitro compound, catalyzed by CYP83A1 (Hemm et al, 2003;Naur et al, 2003), which is then conjugated with a sulfur donor into S-alkyl thiohydroximate. The final biosynthetic steps comprise consecutive actions catalyzed by C-S lyases , UDP-glucosyltransferases (Grubb et al, 2004), and sulfotransferases (ST5b and ST5c; Piotrowski et al, 2004). Recently, the R2R3-MYB transcription factors HAG1/MYB28, HAG2/MYB76, and HAG3/MYB29 were identified as regulators of Met-derived glucosinolate biosynthesis, with High Aliphatic Glucosinolate 1 (HAG1/MYB28) being the main player (Gigolashvili et al, 2007(Gigolashvili et al, , 2008Hirai et al, 2007;Sønderby et al, 2007).…”