Use of the glucosyltransferase UGT71B6 to disturb abscisic acid homeostasis in Arabidopsis thaliana

Abstract

SummaryA glucosyltransferase (GT) of Arabidopsis, UGT71B6, recognizing the naturally occurring enantiomer of abscisic acid (ABA) in vitro, has been used to disturb ABA homeostasis in planta. Transgenic plants constitutively overexpressing UGT71B6 (71B6-OE) have been analysed for changes in ABA and the related ABA metabolites abscisic acid glucose ester (ABA-GE), phaseic acid (PA), dihydrophaseic acid (DPA), 7¢-hydroxyABA and neo-phaseic acid. Overexpression of the GT led to massive accumulation of ABA-GE and reduced levels of the oxidative metabolites PA and DPA, but had marginal effect on levels of free ABA. The control of ABA homeostasis, as reflected in levels of the different metabolites, differed in the 71B6-OEs whether the plants were grown under standard conditions or subjected to wilt stress. The impact of increased glucosylation of ABA on ABA-related phenotypes has also been assessed. Increased glucosylation of ABA led to phenotypic changes in post-germinative growth. The use of two structural analogues of ABA, known to have biological activity but to differ in their capacity to act as substrates for 71B6 in vitro, confirmed that the phenotypic changes arose specifically from the increased glucosylation caused by overexpression of 71B6. The phenotype and profile of ABA and related metabolites in a knockout line of 71B6, relative to wild type, has been assessed during Arabidopsis development and following stress treatments. The lack of major changes in these parameters is discussed in the context of functional redundancy of the multigene family of GTs in Arabidopsis.

Abscisic Acid Uridine Diphosphate Glucosyltransferases Play a Crucial Role in Abscisic Acid Homeostasis in Arabidopsis

“…Suppression of UGT71B6, UGT71B7, and UGT71B8 Causes Hypersensitivity to Exogenous ABA and High-Salt Stress during Germination A previous work showed that UGT71B6 loss-offunction mutant plants did not display any noticeable phenotype (Priest et al, 2006). When we examined single knockout mutants of UGT71B7 or UGT71B8, they did not show any noticeable phenotype (Supplemental Fig.…”

“…Therefore, we examined their gene expression under osmotic stress conditions. The expression of UGT71B6 is induced under high osmotic stress conditions and by the application of exogenous ABA (Priest et al, 2006). To test whether the expression of UGT71B7 and UGT71B8 is regulated under these conditions, 2-week-old wild-type plants were treated with 100 mM ABA, 100 mM NaCl, or 300 mM mannitol for 1 h, and total RNA from these plants was used for qRT-PCR analysis.…”

“…In Arabidopsis (Arabidopsis thaliana), ABA-GE is produced by UGT71B6, an ABA UGT that shows a strict preference for the naturally occurring (+)-ABA enantiomer (Lim et al, 2005). Overexpression of UGT71B6 in planta increases enzyme activity in leaf extracts that can glucosylate ABA in vitro (Priest et al, 2006). However, overexpression of UGT71B6 in Arabidopsis does not cause a significant ABA-deficient phenotype.…”

“…Members of the cytochrome P450 family, CYP707A1 to CYP707A4, hydroxylate ABA at the 89 position to produce unstable 89-hydroxyl ABA, which is converted to phaseic acid by spontaneous isomerization (Kushiro et al, 2004;Okamoto et al, 2006). The conjugation of ABA with Glc is catalyzed by ABA uridine diphosphate glucosyltransferase (UGT) to produce ABA-GE (Xu et al, 2002;Priest et al, 2006). The two catabolic pathways of hydroxylation and conjugation may differ in their consequences for plant physiology.…”

A Co-Opted Hormonal Cascade Activates Dormant Adventitious Root Primordia upon Flooding in Solanum dulcamara

“…The sample preparation for ABA quantitation analysis was performed according to Priest et al (2006), with some modifications. Powder of lyophilized tissue (;5 mg) was extracted with 2 mL of acetone:water (80:20, v/v) in the presence of antioxidant-2,6-di-tert-butyl-4-methylphenol (0.1 mg mL 21 ) and 100 pmol isotope-labeled internal standard [ 2 H 6 ]-ABA.…”