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

Abstract

The phytohormone abscisic acid (ABA) is crucial for plant growth and adaptive responses to various stress conditions. Plants continuously adjust the ABA level to meet physiological needs, but how ABA homeostasis occurs is not fully understood. This study provides evidence that UGT71B6, an ABA uridine diphosphate glucosyltransferase (UGT), and its two closely related homologs, UGT71B7 and UGT71B8, play crucial roles in ABA homeostasis and in adaptation to dehydration, osmotic stress, and high-salinity stresses in Arabidopsis (Arabidopsis thaliana). UGT RNA interference plants that had low levels of these three UGT transcripts displayed hypersensitivity to exogenous ABA and high-salt conditions during germination and exhibited a defect in plant growth. However, the ectopic expression of UGT71B6 in the atbg1 (for b-glucosidase) mutant background aggravated the ABA-deficient phenotype of atbg1 mutant plants. In addition, modulation of the expression of the three UGTs affects the expression of CYP707A1 to CYP707A4, which encode ABA 89-hydroxylases; four CYP707As were expressed at higher levels in the UGT RNA interference plants but at lower levels in the UGT71B6:GFP-overexpressing plants. Based on these data, this study proposes that UGT71B6 and its two homologs play a critical role in ABA homeostasis by converting active ABA to an inactive form (abscisic acid-glucose ester) depending on intrinsic cellular and environmental conditions in plants.

UDP-Glucosyltransferase71C5, a Major Glucosyltransferase, Mediates Abscisic Acid Homeostasis in Arabidopsis

“…UGT71B6 is a glucosytransferase that recognizes the naturally occurring (+)-ABA enantiomer (Priest et al, 2005). Mutation of UGT71B6 (ugt71b6) in Arabidopsis has no obvious ABA-excessive phenotype, whereas cosuppressions of UGT71B6 and its two homologs UGT71B7 and UGT71B8 displayed an ABA-excessive phenotype (Priest et al, 2005;Dong et al, 2014). These findings indicate that UGT71B6 is not a major glucosytransferase involved in ABA homeostasis.…”

“…However, a hypersensitivity to exogenous ABA and high-salt stress during germination in Arabidopsis were seen when UGT71B6, UGT71B7, and UGT71B8 were cosuppressed. This observation indicates that glucosylation of ABA plays a critical role in ABA homeostasis (Dong et al, 2014). Nevertheless, the major ABA glucosyltransferase contributing to glucosylation of ABA to ABA-GE remains to be identified.…”

Glucosylation of 4-Hydroxy-2,5-Dimethyl-3(2H)-Furanone, the Key Strawberry Flavor Compound in Strawberry Fruit

“…UGT71A33, UGT71A34, and UGT71A35, which have been putatively annotated as flavonoid GTs (Shulaev et al, 2011), form a group with FaGT6 that exhibited a broad substrate tolerance in vitro, accepting numerous flavonoids, hydroxycoumarins, and naphthols (Griesser et al, 2008b). However, AtGT71B6, and B7, their close neighbors, have been identified as abscisic acid (ABA):UDP glucosyltransferases recently (Dong et al, 2014).…”

Assessment of the Response of Beta Carotene Enhanced Transgenic Soybeans to Soybean Mosaic Virus (SMV)

“…The methanol extracts were centrifuged at 3,000 ×g for 10 minutes to remove debris and dried under vacuum. The powder was dissolved in 50 ml of 13 Tris-buffered saline buffer (25 mM Tris-HCl, 100 mM NaCl, 0.1 mM MgCl2, and 0.3% [w/v] NaN3), as Dong et al (2014) description. The ABA content was determined by competitive ELISA using an anti-ABA antibody according to the protocol of the Phytodetek ABA Test Kit (Agdia Inc.).…”