BHLH transcription factors facilitating K+ uptake during stomatal opening are repressed by abscisic acid through phosphorylation

ABSTRACT: Stomata open in response to light and close following exposure to abscisic acid (ABA). They regulate gas exchange between plants and atmosphere, allowing plants to adapt to changing environmental conditions. ABA binding to receptors initiates a signaling cascade that involves protein phosphorylation. Here we show that ABA induced phosphorylation of three basic helix-loop-helix (bHLH) transcription factors, called AKSs (ABA-RESPONSIVE KINASE SUBSTRATES; AKS1, AKS2, AKS3), in Arabidopsis guard cells, and that they 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. 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 transcription of genes encoding inwardly-rectifying K+ channels, and that ABA suppresses the activity of inwardly-rectifying K+ channel activity by triggering the phosphorylation of these transcription factors. To find the affect of AKS1 and AKS2 transcription factors on gene expression, Arabidopsis guard cell protoplasts from wild type and aks1aks2-1 mutant were compared. Three independent experiments were performed.

ORGANISM(S): Arabidopsis thaliana

SUBMITTER: Yohei Takahashi 

PROVIDER: E-GEOD-46574 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress