Plants have evolved complex physiological and biochemical mechanisms to adapt to a heterogeneous soil phosphorus environment. PHOSPHATE2 (PHO2) is a phosphate (Pi) starvation-signaling regulator involved in maintaining Pi homeostasis in plants. Arabidopsis (Arabidopsis thaliana) PHO2 targets PHOSPHATE TRANSPORTER1 (PHT1) and PHO1 for degradation, whereas rice (Oryza sativa) PHO2 is thought to mediate PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 degradation. However, it is unclear whether and how PHO2 is post-translationally regulated. Here, we show that in rice, the CASEIN KINASE2 (OsCK2) catalytic subunit OsCK2α3 interacts with OsPHO2 in vitro and in vivo in vascular tissues cells, and phosphorylates OsPHO2 at Ser-841. Phosphorylated OsPHO2 is degraded more rapidly than native OsPHO2 in cell-free degradation assays. OsPHO2 interacts with OsPHO1 and targets it for degradation through a multivesicular body-mediated pathway. PHO1 mutation partially rescued the pho2 mutant phenotype. Further genetic analysis showed that a nonphosphorylatable version of OsPHO2 rescued the Ospho2 phenotype of high Pi accumulation in leaves better than native OsPHO2. In addition to the previously established role of OsCK2 in negatively regulating endoplasmic reticulum exit of PHT1 phosphate transporters, this work uncovers a role for OsCK2α3 in modulating Pi homeostasis through regulating the phosphorylation status and abundance of OsPHO2 in rice.

中文翻译：

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酪蛋白激酶2依赖的磷酸化磷酸化PHOSPHATE2可以精确调节水稻中的磷酸稳态。

植物已经进化出复杂的生理和生化机制，以适应异质土壤磷环境。PHOSPHATE2（PHO2）是一种磷酸盐（Pi）饥饿信号调节剂，参与植物体内Pi稳态的维持。拟南芥（Arabidopsis thaliana）PHO2靶向降解PHOSPHATE TRANSPORTER1（PHT1）和PHO1，而水稻（Oryza sativa）PHO2被认为介导了PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1降解。但是，尚不清楚PHO2是否以及如何被翻译后调节。在这里，我们显示了在水稻中，酪蛋白激酶2（OsCK2）催化亚基OsCK2α3在体内和体外在血管组织细胞中与OsPHO2相互作用，并在Ser-841处磷酸化OsPHO2。在无细胞降解试验中，磷酸化的OsPHO2的降解速度比天然OsPHO2更快。OsPHO2与OsPHO1相互作用，并通过多囊体介导的途径使其降解。PHO1突变部分拯救了pho2突变表型。进一步的遗传分析表明，OsPHO2的非磷酸化形式比天然OsPHO2更好地挽救了叶片中高Pi积累的Ospho2表型。除了先前确定的OsCK2在负调节PHT1磷酸转运蛋白的内质网出口中的作用外，这项工作还揭示了OsCK2α3通过调节水稻中OsPHO2的磷酸化状态和丰度来调节Pi稳态的作用。进一步的遗传分析表明，OsPHO2的非磷酸化形式比天然OsPHO2更好地挽救了叶片中高Pi积累的Ospho2表型。除了先前确定的OsCK2在负调节PHT1磷酸转运蛋白的内质网出口中的作用外，这项工作还揭示了OsCK2α3通过调节水稻中OsPHO2的磷酸化状态和丰度来调节Pi稳态的作用。进一步的遗传分析表明，OsPHO2的非磷酸化形式比天然OsPHO2更好地挽救了叶片中高Pi积累的Ospho2表型。除了先前确定的OsCK2在负调节PHT1磷酸转运蛋白的内质网出口中的作用外，这项工作还揭示了OsCK2α3通过调节水稻中OsPHO2的磷酸化状态和丰度来调节Pi稳态的作用。