bHLH Transcription Factors That Facilitate K+ Uptake During Stomatal Opening Are Repressed by Abscisic Acid Through Phosphorylation.
by Takahashi Y., Ebisu Y., Kinoshita T., Doi M., Okuma E., Murata Y., Shimazaki K. (2013)
- Yohei Takahashi1,
- Yuta Ebisu2,
- Toshinori Kinoshita1,*,
- Michio Doi3,
- Eiji Okuma4,
- Yoshiyuki Murata4, and
- Ken-ichiro Shimazaki1,†
1Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
2Graduate School of System Life Sciences, Kyushu University, Fukuoka 812-8581, Japan.3Center for Research and Advancement in Higher Education, Kyushu University, Fukuoka 819-0395, Japan. 4Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
in Sci Signal. 2013 Jun 18 6(280):ra48. doi: 10.1126/scisignal.2003760 –
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.