State Key Laboratory of Plant Environmental Resilience, College of Biological Sciences, Frontiers Science Center for Molecular Design Breeding (MOE), China Agricultural University, Beijing, China.
State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences and School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China.
Nat Plants. 2024 May;10(5):798-814. doi: 10.1038/s41477-024-01679-y. Epub 2024 May 7.
Phytochrome A (phyA) is the plant far-red (FR) light photoreceptor and plays an essential role in regulating photomorphogenic development in FR-rich conditions, such as canopy shade. It has long been observed that phyA is a phosphoprotein in vivo; however, the protein kinases that could phosphorylate phyA remain largely unknown. Here we show that a small protein kinase family, consisting of four members named PHOTOREGULATORY PROTEIN KINASES (PPKs) (also known as MUT9-LIKE KINASES), directly phosphorylate phyA in vitro and in vivo. In addition, TANDEM ZINC-FINGER/PLUS3 (TZP), a recently characterized phyA-interacting protein required for in vivo phosphorylation of phyA, is also directly phosphorylated by PPKs. We reveal that TZP contains two intrinsically disordered regions in its amino-terminal domain that undergo liquid-liquid phase separation (LLPS) upon light exposure. The LLPS of TZP promotes colocalization and interaction between PPKs and phyA, thus facilitating PPK-mediated phosphorylation of phyA in FR light. Our study identifies PPKs as a class of protein kinases mediating the phosphorylation of phyA and demonstrates that the LLPS of TZP contributes significantly to more production of the phosphorylated phyA form in FR light.
光敏色素 A（phyA）是植物远红光（FR）光受体，在调节 FR 丰富条件下的光形态建成发育中发挥着重要作用，例如树冠遮荫。长期以来，人们观察到 phyA 是体内的一种磷酸化蛋白；然而，能够磷酸化 phyA 的蛋白激酶在很大程度上仍不清楚。在这里，我们表明，由四个成员组成的小蛋白激酶家族，称为光调节蛋白激酶（PPKs）（也称为 MUT9 样激酶），可直接在体外和体内磷酸化 phyA。此外，TANDEM ZINC-FINGER/PLUS3（TZP），一种最近被表征的 phyA 相互作用蛋白，是体内磷酸化 phyA 所必需的，也可被 PPKs 直接磷酸化。我们揭示了 TZP 在其氨基末端结构域中包含两个固有无序区域，在暴露于光时会发生液-液相分离（LLPS）。TZP 的 LLPS 促进了 PPKs 和 phyA 之间的共定位和相互作用，从而促进了 FR 光中 PPK 介导的 phyA 磷酸化。我们的研究确定了 PPKs 作为一类介导 phyA 磷酸化的蛋白激酶，并表明 TZP 的 LLPS 显著促进了 FR 光中磷酸化的 phyA 形式的更多产生。
