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Abstract

Glucosinolates are defensive compounds found in several plant families. We recently described five distinct isoforms of a novel plant enzyme, thiol methyltransferase (TMT), which methylate the hydrolysis products of glucosinolates to volatile sulfur compounds that have putative anti-insect and anti-pathogen roles. In the work presented here, two cDNAs encoding these enzymes (cTMT1 and cTMT2) were isolated by screening a cabbage cDNA library with an Arabidopsis EST showing high sequence homology to one TMT isoform. The genomic clone of cTMT1 was subsequently amplified by PCR. Both cDNAs encoded polypeptides of identical lengths (227 amino acids) and similar predicted masses (ca. 25 kDa), but differing in 13 residues. The cDNAs contained the typical methyltransferase signatures, but were otherwise distinct from conventionally known N-, O- or S-methyltransferases. A chloride methyl transferase was the only gene with an assigned function that shared significant similarity with the TMT cDNAs. Southern analysis indicated single copy for each TMT gene. The two cDNAs were expressed in Escherichia coli. The substrate range, kinetic properties and molecular sizes of the purified recombinant proteins were comparable to those of the native enzyme. These data, together with the detection of the sequenced amino acid motif of one native TMT peptide in the cDNAs, confirmed that the latter were authentic TMTs. The expression pattern of the TMTs in various cabbage tissues was consistent with their association with glucosinolates. The cloning of this new class of plant genes furnishes crucial molecular tools to understand the role of this metabolic sector in plant defenses against biotic stress.

Proteomic Analysis of Lipid Droplets from Arabidopsis Aging Leaves Brings New Insight into Their Biogenesis and Functions

“…As mentioned before, the glucosinolate catabolism generates a variety of toxic breakdown products involved in plant defense against biotic stress. In the presence of SAM, thiol methyltransferases catalyze the methylation of these compounds into less toxic products associated with airborne plant-insect signals and plant-pathogen interactions (Attieh et al, 2000, 2002). (iii) SAM is involved in the recycling of prenylated proteins: when isoprenylated proteins transit throught the ER, the prenylcysteine is methylated by an isoprenylcysteine methyltransferase with SAM as methyl donor.…”

Arabidopsis HARMLESS TO OZONE LAYER Protein Methylates a Glucosinolate Breakdown Product and Functions in Resistance to Pseudomonas syringae pv. maculicola

“…1) purified from soluble fractions (supplemental Fig. S3), which permitted more proper folding of the proteins than those prepared from insoluble fractions as done in previous studies (11,13). Enzymatic activities for the three substrates were largely distinct among AtHOL isoforms ( Table 1).…”

“…methylate the thiocyanate ion (NCS Ϫ ), which is called pseudohalide because of its chemical properties similar to halide ions (13,14). NCS Ϫ is a hydrolysis product found in some glucosinolates, which are secondary metabolites found mainly in the order Brassicales including the model plant Arabidopsis thaliana (15).…”

Real-time analysis of sulfur-containing volatiles in Brassica plants infested with root-feeding Delia radicum larvae using proton-transfer reaction mass spectrometry

“…High levels of thiol methyltransferase (TMT) activities have been found in shoots and roots of various Brassica species (Saini et al 1995; Attieh et al 2002). This enzyme is thought to have a function in detoxifying the phytotoxic sulfur-containing (by)products of glucosinolate conversion, such as cyanides and HS − ions (Attieh et al 2000).…”