title: bHLH transcription factors that facilitate K⁺ uptake during stomatal opening are repressed by abscisic acid through phosphorylation.
abstract: Stomata open in response to light and close after exposure to abscisic acid (ABA). They regulate gas exchange between plants and the atmosphere, enabling plants to adapt to changing environmental conditions. ABA binding to receptors initiates a signaling cascade that involves protein phosphorylation. We show that ABA induced the phosphorylation of three basic helix-loop-helix (bHLH) transcription factors, called AKSs (ABA-responsive kinase substrates; AKS1, AKS2, and AKS3), in Arabidopsis guard cells. In their unphosphorylated state, AKSs facilitated stomatal opening through the transcription of genes encoding inwardly rectifying K⁺ channels. aks1aks2-1 double mutant plants showed decreases in light-induced stomatal opening, K⁺ accumulation in response to light, activity of inwardly rectifying K⁺ channels, and transcription of genes encoding major inwardly rectifying K⁺ channels without affecting ABA-mediated stomatal closure. Overexpression of potassium channel in Arabidopsis thaliana 1 (KAT1), which encodes a major inwardly rectifying K⁺ channel in guard cells, rescued the phenotype of aks1aks2-1 plants. AKS1 bound directly to the promoter of KAT1, an interaction that was attenuated after ABA-induced phosphorylation. The ABA agonist pyrabactin induced phosphorylation of AKSs. Our results demonstrate that the AKS family of bHLH transcription factors facilitates stomatal opening through the transcription of genes encoding inwardly rectifying K⁺ channels and that ABA suppresses the activity of these channels by triggering the phosphorylation of AKS family transcription factors.
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yuta
authors.initials: Y
authors.lastname: Ebisu
authors.forename: Toshinori
authors.initials: T
authors.lastname: Kinoshita
authors.forename: Michio
authors.initials: M
authors.lastname: Doi
authors.forename: Eiji
authors.initials: E
authors.lastname: Okuma
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Murata
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Shimazaki
mesh_terms: D000040:Abscisic Acid / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D009154:Mutation; D009281:Naphthalenes / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D054046:Plant Stomata / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000096:biosynthesis / Q000235:genetics; D020218:Response Elements / Q000502:physiology; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D009281:Naphthalenes; D011188:Potassium; D024661:Potassium Channels, Inwardly Rectifying; D044843:SKP Cullin F-Box Protein Ligases; D013449:Sulfonamides; C120363:ASK1 protein, Arabidopsis; C501210:KAT1 protein, Arabidopsis; C540973:pyrabactin; C484058:ASK2 protein, Arabidopsis