磷酸酶ABI2作为ABA受体PYLs的直接下游组分，在种子休眠与萌发、幼苗生长等方面负向调控ABA信号途径。我们以前的研究表明，在ABA信号通路中，ABI2第三个钙依赖型蛋白激酶磷酸化位点在ABI2与PYLs及SnRK2.6的相互作用中起着关键作用。对ABI2的结构分析发现，该位点位于P-loop区，暗示ABI2具有结合ATP/GTP的潜力。本项目拟通过ITC技术来验证ABI2能否结合ATP；同时，以拟南芥为实验材料，采用氨基酸突变、酶活测定、酵母双杂、基因转化等方法，研究ABI2第三个磷酸化位点氨基酸突变对ABI2磷酸酶活性、ATP结合活性、蛋白互作及ABA相关表型的影响，找出ABI2中介导ABA信号的关键氨基酸位点，揭示其介导ABI2参与ABA信号转导的功能及作用机制，这对于深入理解ABI2在ABA原初信号中的精细调控机制具有重要作用，将为基因改良、创制优异种质资源提供重要的理论参考。

It has been known that clade A protein phosphatase 2C (PP2C), including ABI2 PP2C, are key players that function directly downstream of the PYR/PYL/RCAR ABA receptors. As a negative regulator of ABA signaling, ABI2 plays crucial roles in seed dormancy and germination, seedling growth and stomatal movement. .Our previous results showed that, the third calcium-dependent protein kinase (CDPK) phosphorylation site (3rd CPS) of ABI2 plays a key role in the ABI2 interaction with PYL5/PYL9 and SnRK2.6 in ABA signaling. It was found that the third phosphorylation site of ABI2 is located at a P-loop domain (which is able to bind ATP/GTP) by Bioinformatics analysis, indicating that ABI2 has the potential to bind ATP/GTP. In this project, we will verify this by ITC (Isothermal Titration Calorimetry) experiment, at the same time, we will use Arabidopsis thaliana (wild type and ABI2 T-DNA insertion mutant) to investigate the function of the pivotal site of ABI2 in ABA signaling transduction. We will use site-directed mutagenesis to mutate the amino acids of ABI2 3rd CPS firstly, and then we will analyze the potential effect of ABI2 phosphatase activity, ATP binding activity and the ABI2 interaction with its relative interacting proteins (such as PYLs and SnRK2s) caused by the amino acid mutation of the 3rd CPS through different molecular methods, such as yeast two hybrid, the determination of ATP binding activity, ABI2 phosphatase activity and plant genetic transformation analyze. .Overall, our study will elucidate the function and mechanism of the pivotal site of ABI2 3rd CPS in ABA signaling, which may provide new crucial information to deeply understand the fine-tuning mechanism of ABI2 in ABA original signal transduction, and which will also provide an important theoretical reference for genetic improvement and creation of excellent germplasm resources.