UGT74D1 Is a Novel Auxin Glycosyltransferase from Arabidopsis thaliana

Abstract

Auxin is one type of phytohormones that plays important roles in nearly all aspects of plant growth and developmental processes. The glycosylation of auxins is considered to be an essential mechanism to control the level of active auxins. Thus, the identification of auxin glycosyltransferases is of great significance for further understanding the auxin regulation. In this study, we biochemically screened the group L of Arabidopsis thaliana glycosyltransferase superfamily for enzymatic activity toward auxins. UGT74D1 was identified to be a novel auxin glycosyltransferase. Through HPLC and LC-MS analysis of reaction products in vitro by testing eight substrates including auxins and other compounds, we found that UGT74D1 had a strong glucosylating activity toward indole-3-butyric acid [IBA], indole-3-propionic acid [IPA], indole-3-acetic acid [IAA] and naphthaleneacetic acid [NAA], catalyzing them to form corresponding glucose esters. Biochemical characterization showed that this enzyme had a maximum activity in HEPES buffer at pH 6.0 and 37°C. In addition, the enzymatic activity analysis of crude protein and the IBA metabolite analysis from transgenic Arabidopsis plants overexpressing UGT74D1 gene were also carried out. Experimental results indicated that over-production of the UGT74D1 in plants indeed led to increased level of the glucose conjugate of IBA. Moreover, UGT74D1 overexpression lines displayed curling leaf phenotype, suggesting a physiological role of UGT74D1 in affecting the activity of auxins. Our current data provide a new target gene for further genetic studies to understand the auxin regulation by glycosylation in plants.

UGT74D1 Catalyzes the Glucosylation of 2-Oxindole-3-Acetic Acid in the Auxin Metabolic Pathway in Arabidopsis

“…However, OxIAA was not investigated as a naturally occurring substrate (Jin et al 2013). To investigate directly if UGT74D1 exhibits glucosyltransferase activity against OxIAA, we expressed glutathione S -transferase (GST) fused with UGT74D1 (GST–UGT74D1) in E. coli for use in an enzyme assay.…”

Auxin-Induced Modulation of ETTIN Activity Orchestrates Gene Expression in Arabidopsis

“…UDP-glycosyltransferases are enzymes capable of adding a glucose molecule to a set of molecular targets, including hormones. Indeed, the UDP-glycosyltransferases UGT84B1, UGT74E2, and UGT74D1 can all add sugar molecules to auxins, in particular, IAA and indole-3-butyric acid, and may thereby alter the activity, solubility, and cellular localization of auxin (Jackson et al, 2001;Tognetti et al, 2010;Jin et al, 2013). As phyllotaxis is tightly dependent on auxin accumulation and transport (Reinhardt et al, 2003;Jönsson et al, 2006;Smith et al, 2006), TEC3 may therefore contribute to the control of auxin homeostasis in the shoot apical meristem.…”

Indole-3-acetic acid UDP-glucosyltransferase from immature seeds of pea is involved in modification of glycoproteins

“…Another A. thaliana enzyme, AtUGT74E2 preferred IBA, NAA, JA, and 2-4 D more than IAA for glucosylation, as reported by Tognetti et al (2010). Recently, Jin et al (2013) have identified the UGT74D1 that catalyzes predominantly synthesis of IBA-and IPA-glucose, but is also able to conjugate IAA and NAA.…”

“…The biological significance of glucosyltransferases synthesizing conjugates of various auxins is an intriguing problem. It cannot be excluded that diversity of these enzymes is associated with the functional redundancy as proposed by Jin et al (2013). On the other hand, the occurrence of glucosyltransferases with a broad substrate preference may be a result of different expression pattern of UGT genes during plant development.…”

“…On the other hand, a knock out mutation of UGT74E2 did not affect the phenotype of plants suggesting that the A. thaliana genome contains more genes which encode IBA-glucosyltransferases. For example, the UGT74D1 enzyme from A. thaliana can glucosylate both IAA and IBA (Jin et al, 2013).…”