A dynamic model of the ABA Signaling pathway with its core components: translation rate of PP2C determines the kinetics of ABA-induced gene expression

The abscisic acid (ABA) signaling pathway is the key defense mechanism against drought stress in plants, yet the connectivity of cellular molecules related to gene expression in response to ABA is little understood. A dynamic model of the core components of the ABA signaling pathway was built using ordinary differential equations to understand the connectivity. Parameter values of protein-protein interactions and enzymatic reactions in the model were implemented from the data obtained by previously conducted experiments. On the other hand, parameter values of gene expression and translation were determined by comparing the kinetics of gene expression in the model to those of ABA-induced RD29A (response to desiccation 29A) in actual plants. Based on the analyses of the optimized model, we hypothesized that the translation rate of PP2C (protein phosphatase type 2C) is downregulated by ABA to increase the ABRE (ABA-responsive element) promoter activity. The hypotheses were preliminarily supported by newly conducted experiments using transgenic Arabidopsis plants that carry a luciferase expression cassette driven by the RD29A promoter (RD29A::LUC). The model suggests that identifying a mechanism that alters PP2C translation rate would be one of the next research frontiers in the ABA signaling pathway.