Title Desulfo-glucosinolate Sulfotransferases from Arabidopsis Thaliana Catalyzing the Final Step in Biosynthesis of the Glucosinolate Core Structure

Running Title desulfo-Glucosinolate sulfotransferases from Arabidopsis thaliana SUMMARY The phytotoxin coronatine is a structural analog of octadecanoid signaling molecules which are well known mediators of plant defense reactions. In order to isolate novel coronatine-regulated genes from Arabidopsis thaliana, differential mRNA display was performed. Transcript levels of CORI-7 (coronatine induced) 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, 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 core structure, the sulfation of desulfo-glucosinolates. They accept a broad range of desulfo-glucosinolates as substrates. However, in a competitive situation AtST5a clearly prefers tryptophan-and phenylalanine-derived desulfo-glucosinolates while long-chain desulfo-glucosinolates 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 glucosinolates, primarily glucobrassicin and neoglucobrassicin. Hence, it is suggested that AtST5a is the sulfotransferase responsible for the biosynthesis of tryptophan-derived glucosinolates in vivo.