Metabolism of salicylic acid in wild‐type, ugt74f1 and ugt74f2 glucosyltransferase mutants of Arabidopsis thaliana

Abstract

Arabidopsis thaliana contains two salicylic acid (SA) glucosyltransferase enzymes designated UGT74F1 and UGT74F2. UGT74F1 forms only SA 2-O-beta-D-glucose (SAG), while UGT74F2 forms both SAG and the SA glucose ester (SGE). In an attempt to determine the in vivo role of each SA glucosyltransferase (SAGT), the metabolism of SA in ugt74f1 and ugt74f2 mutants was examined and compared with that of the wild-type. The three major metabolites formed in wild-type Arabidopsis included SAG, SGE, and 2,5-dihydroxbenzoic acid 2-O-beta-D-glucose (DHB2G). This is the first description of DHB2G as a major metabolite of SA in plants. The major metabolites of SA formed in ugt74f1 mutants were SGE, SAG and 2,5-dihydroxybenzoic acid 5-O-beta-D-glucose (DHB5G). DHB5G was not formed in the wild-type plants. SAG and DHB2G were the main metabolites of SA in ugt74f2 mutants. The ugt74f2 mutant was unable to form SGE. Only SGE could be detected during in vitro SAGT assays of untreated wild-type and ugt74f1 mutants. This activity was because of constitutive UGT74F2 activity. Both SGE and SAG could be formed during in vitro assays of SA-pretreated wild-type and ugt74f1 leaves. Neither SAG nor SGE could be detected during the in vitro SAGT assays of untreated ugt74f2 leaves. Only SAG was formed during the in vitro SAGT assays of SA-pretreated ugt74f2 leaves. The SAG formation was a result of the UGT74F1 activity. This work demonstrates that changes in the activity of either SAGT enzyme can have a dramatic effect on the metabolism of exogenously supplied SA in Arabidopsis.

Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins

“…3. Other characterized UGT74 enzymes include an indole-3-acetic acid GT (ZmIAGT) from Z. mays (21), a crocetin GT (CsUGT2) from Crocus sativus (22), a gentisic acid xylosyltransferase from Solanum lycopersicum (SlGAGT) (23), a salicylic acid GT from Nicotiana tabacum (NtSAGTase) (24), a salicylic acid/anthranilic acid GT (UGT74F2), a thiohydroximate GT (AtUGT74B1) and a jasmonate GT (AtUGT74D1) from A. thaliana (25)(26)(27), and a triterpene GT from Saponaria vaccaria (synonym Vaccaria hispanica) (SvUGT74M1) that catalyzes the addition of glucose onto gypsogenic acid (28). A. thaliana UGT74E2 is thought to be an auxin indole-3-butyric acid glucosyltransferase (29) and UGT74C1 is implicated in aliphatic glucosinolate biosynthesis (30).…”

Salicylic Acid Biosynthesis and Metabolism

“…Arabidopsis encodes at least two UDP-glucosyltransferases that glucosylate SA, UGT74F1 and UGT74F2, (also referred to as AtSGT1; Lim et al, 2002;Song, 2006;Dean and Delaney, 2008). UGT74F1, encoded by At2g43840, and UGT74F2, encoded by At2g43820, both catalyze the conjugation of SA at its hydroxyl group resulting in the formation of SA 2-O-β-D-glucoside (SAG).…”

Transient increase in salicylic acid and its glucose conjugates after wounding in Arabidopsis leaves

“…Induction of salicylic acid glucose conjugates concomitantly with or slightly delayed relative to induction of salicylic acid is often seen in the response of plants infected with an avirulent pathogen (Delaney et al 1994;Malamy et al 1990). The conjugates seem to function to detoxify salicylic acid (Dean and Delaney 2008;Hennig et al 1993;Lee and Raskin 1998;Lim et al 2002;Quiel and Bender 2003; Ratzinger et al 2009). The basal level of salicylic acid at 24 hours after wounding may reflect the highest accumulation of SAG and SGE, which are converted from salicylic acid, at this time point.…”