Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520-8104, USA.
Plant Cell. 2013 Feb;25(2):517-34. doi: 10.1105/tpc.112.105767. Epub 2013 Feb 12.
The basic Leucine zipper transcription factor ABSCISIC ACID INSENSITIVE5 (ABI5) is a key regulator of abscisic acid (ABA)-mediated seed germination and postgermination seedling growth. While a family of SUCROSE NONFERMENTING1-related protein kinase2s (SnRK2s) is responsible for ABA-induced phosphorylation and stabilization of ABI5, the phosphatase(s) responsible for dephosphorylating ABI5 is still unknown. Here, we demonstrate that mutations in FyPP1 (for Phytochrome-associated serine/threonine protein phosphatase1) and FyPP3, two homologous genes encoding the catalytic subunits of Ser/Thr PROTEIN PHOSPHATASE6 (PP6), cause an ABA hypersensitive phenotype in Arabidopsis thaliana, including ABA-mediated inhibition of seed germination and seedling growth. Conversely, overexpression of FyPP causes reduced sensitivity to ABA. The ABA hypersensitive phenotype of FyPP loss-of-function mutants is ABI5 dependent, and the amount of phosphorylated and total ABI5 proteins inversely correlates with the levels of FyPP proteins. Moreover, FyPP proteins physically interact with ABI5 in vitro and in vivo, and the strength of the interaction depends on the ABI5 phosphorylation status. In vitro phosphorylation assays show that FyPP proteins directly dephosphorylate ABI5. Furthermore, genetic and biochemical assays show that FyPP proteins act antagonistically with SnRK2 kinases to regulate ABI5 phosphorylation and ABA responses. Thus, Arabidopsis PP6 phosphatase regulates ABA signaling through dephosphorylation and destabilization of ABI5.
基本亮氨酸拉链转录因子脱落酸不敏感 5（ABI5）是脱落酸（ABA）介导的种子萌发和萌发后幼苗生长的关键调节剂。虽然蔗糖非发酵 1 相关蛋白激酶 2 家族（SnRK2s）负责 ABA 诱导的 ABI5 磷酸化和稳定，但负责去磷酸化 ABI5 的磷酸酶仍然未知。在这里，我们证明 FyPP1（phytochrome 相关丝氨酸/苏氨酸蛋白磷酸酶 1 的缩写）和 FyPP3 的突变，这两个同源基因编码丝氨酸/苏氨酸蛋白磷酸酶 6（PP6）的催化亚基，导致拟南芥对 ABA 超敏，包括 ABA 介导的抑制种子萌发和幼苗生长。相反，FyPP 的过表达导致对 ABA 的敏感性降低。FyPP 功能丧失突变体的 ABA 超敏表型依赖于 ABI5，磷酸化和总 ABI5 蛋白的量与 FyPP 蛋白的水平成反比。此外，FyPP 蛋白在体外和体内与 ABI5 相互作用，相互作用的强度取决于 ABI5 的磷酸化状态。体外磷酸化实验表明，FyPP 蛋白直接去磷酸化 ABI5。此外，遗传和生化实验表明，FyPP 蛋白与 SnRK2 激酶相互拮抗，以调节 ABI5 磷酸化和 ABA 反应。因此，拟南芥 PP6 磷酸酶通过去磷酸化和 ABI5 失稳来调节 ABA 信号转导。
