Shanghai Center for Plant Stress Biology and Center of Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
Nat Commun. 2021 Dec 2;12(1):7040. doi: 10.1038/s41467-021-27391-5.
Phosphate, a key plant nutrient, is perceived through inositol polyphosphates (InsPs) by SPX domain-containing proteins. SPX1 an inhibit the PHR2 transcription factor to maintain Pi homeostasis. How SPX1 recognizes an InsP molecule and represses transcription activation by PHR2 remains unclear. Here we show that, upon binding InsP, SPX1 can disrupt PHR2 dimers and form a 1:1 SPX1-PHR2 complex. The complex structure reveals that SPX1 helix α1 can impose a steric hindrance when interacting with the PHR2 dimer. By stabilizing helix α1, InsP allosterically decouples the PHR2 dimer and stabilizes the SPX1-PHR2 interaction. In doing so, InsP further allows SPX1 to engage with the PHR2 MYB domain and sterically block its interaction with DNA. Taken together, our results suggest that, upon sensing the surrogate signals of phosphate, SPX1 inhibits PHR2 via a dual mechanism that attenuates dimerization and DNA binding activities of PHR2.
磷酸盐是一种关键的植物营养物质，可被含有 SPX 结构域的蛋白质通过肌醇多磷酸盐（InsPs）感知。SPX1 可抑制 PHR2 转录因子以维持磷稳态。然而，SPX1 如何识别 InsP 分子并抑制 PHR2 的转录激活仍不清楚。在这里，我们发现，在结合 InsP 后，SPX1 可以破坏 PHR2 二聚体并形成 1:1 的 SPX1-PHR2 复合物。该复合物结构表明，SPX1 的α1 螺旋在与 PHR2 二聚体相互作用时会产生空间位阻。通过稳定α1 螺旋，InsP 变构地使 PHR2 二聚体解偶联并稳定 SPX1-PHR2 相互作用。这样，InsP 进一步允许 SPX1 与 PHR2 MYB 结构域结合，并在空间上阻止其与 DNA 的相互作用。总之，我们的结果表明，在感知磷酸盐的替代信号后，SPX1 通过两种机制抑制 PHR2，从而减弱 PHR2 的二聚化和 DNA 结合活性。
