title: A vacuolar β-glucosidase homolog that possesses glucose-conjugated abscisic acid hydrolyzing activity plays an important role in osmotic stress responses in Arabidopsis.
abstract: The phytohormone abscisic acid (ABA) plays a critical role in various physiological processes, including adaptation to abiotic stresses. In Arabidopsis thaliana, ABA levels are increased both through de novo biosynthesis and via β-glucosidase homolog1 (BG1)-mediated hydrolysis of Glc-conjugated ABA (ABA-GE). However, it is not known how many different β-glucosidase proteins produce ABA from ABA-GE and how the multiple ABA production pathways are coordinated to increase ABA levels. Here, we report that a previously undiscovered β-glucosidase homolog, BG2, produced ABA by hydrolyzing ABA-GE and plays a role in osmotic stress response. BG2 localized to the vacuole as a high molecular weight complex and accumulated to high levels under dehydration stress. BG2 hydrolyzed ABA-GE to ABA in vitro. In addition, BG2 increased ABA levels in protoplasts upon application of exogenous ABA-GE. Overexpression of BG2 rescued the bg1 mutant phenotype, as observed for the overexpression of NCED3 in bg1 mutants. Multiple Arabidopsis bg2 alleles with a T-DNA insertion in BG2 were more sensitive to dehydration and NaCl stress, whereas BG2 overexpression resulted in enhanced resistance to dehydration and NaCl stress. Based on these observations, we propose that, in addition to the de novo biosynthesis, ABA is produced in multiple organelles by organelle-specific β-glucosidases in response to abiotic stresses.
authors.affiliation: Division of Molecular and Life Science, Pohang University of Science and Technology, Pohang 790-784, Korea.
authors.forename: Zheng-Yi
authors.initials: ZY
authors.lastname: Xu
authors.forename: Kwang Hee
authors.initials: KH
authors.lastname: Lee
authors.forename: Ting
authors.initials: T
authors.lastname: Dong
authors.forename: Jae Cheol
authors.initials: JC
authors.lastname: Jeong
authors.forename: Jing Bo
authors.initials: JB
authors.lastname: Jin
authors.forename: Yuri
authors.initials: Y
authors.lastname: Kanno
authors.forename: Dae Heon
authors.initials: DH
authors.lastname: Kim
authors.forename: Soo Youn
authors.initials: SY
authors.lastname: Kim
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Seo
authors.forename: Ray A
authors.initials: RA
authors.lastname: Bressan
authors.forename: Dae-Jin
authors.initials: DJ
authors.lastname: Yun
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D044602:Cellulases / Q000235:genetics / Q000378:metabolism*; D003890:Desiccation; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics; D009995:Osmosis / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D029681:Arabidopsis Proteins; C077263:BG2 protein, Arabidopsis; D012965:Sodium Chloride; D000040:Abscisic Acid; D044602:Cellulases