水稻OsPHO2通过蛋白磷酸酶OsPHPP1调控磷吸收及转运的机制研究

Phosphorus is an essential mineral macronutrient for plant development and reproduction, and is also a major constituent of the fertilizers required to sustain high-yield agriculture. The ubiquitin E2 conjugase PHO2 functions as a negative regulator in phosphate (Pi) uptake from soil and translocation from root to shoot. However, the functions of PHO2 has not been well-studied in rice. Although some AtPHT1 members could be directly degraded by AtPHO2 in Arabidopsis, rice OsPHO2 could not interact with OsPHT1 members. We identified a protein phosphatase OsPHPP1 that could interact with OsPHO2. OsPHPP1 protein was induced upon Pi starvation, and the degradation rate of OsPHPP1 responsed to Pi level. Overexpression of OsPHPP1 in rice resulted in Pi content and OsPHT1;8 protein accumulation. In addition, OsPHT1;8 protein is accumulated in Ospho2 mutant. We speculated that OsPHO2 could regulate OsPHT1;8 protein level via OsPHPP1 to maintain Pi homeostasis in rice. In this project, we will focus on the function of OsPHPP1 in Pi homeostasis and the regulatory mechanism among OsPHO2, OsPHPP1 and OsPHT1;8. This research will illuminate the mechanism of OsPHO2 in regulating phosphate uptake and translocation via protein phosphatase OsPHPP1 in rice，provide a new insight into mechanism of phosphate uptake and homeostasis, and build a solid theoretical foundation for improvement of phosphorus efficiency in crops.

磷是植物生长发育所必需的大量矿质元素之一，同时也是维持作物高产的主要肥料之一。PHO2作为一种泛素连接酶E2，在调控植物磷吸收及转运的过程中起负调控作用，但其在水稻中的功能尚未完全解析。我们前期研究发现一个蛋白磷酸酶OsPHPP1，其能够与OsPHO2相互作用；OsPHPP1蛋白受缺磷条件诱导，且其蛋白的降解速率与供磷条件相关；超表达OsPHPP1能够提高水稻的磷含量，并提高OsPHT1;8的蛋白水平。另外，我们发现OsPHT1;8蛋白在Ospho2突变体中积累。我们推测OsPHO2可能通过OsPHPP1调节OsPHT1;8蛋白水平从而调控水稻对磷的吸收及转运。因此本项目将深入分析OsPHO2、OsPHPP1和OsPHT1;8之间的调控机理，阐明OsPHO2通过OsPHPP1调控水稻磷吸收及转运的分子机制，进一步丰富和完善植物磷吸收利用调控网络，为作物磷高效育种奠定理论基础。

磷是植物生长发育所必需的矿质营养元素之一。磷素的高效吸收主要依赖于质膜定位的PHT1磷酸盐转运蛋白家族，而该家族蛋白的大多数蛋白在内质网合成之后会被蛋白激酶CK2磷酸化，从而抑制其转运至质膜。因此，鉴定负责去磷酸化PHT1的蛋白磷酸酶对提高水稻磷素吸收效率具有重要意义。在本项目的支持下，我们通过生理生化分析、遗传互作分析、蛋白互作分析等手段，鉴定到一个蛋白磷酸酶PHPP1，该蛋白能够去磷酸化由蛋白激酶CK2引起的PHT1磷酸化。超表达PHPP1促进水稻磷素吸收，而突变该基因会改变水稻磷素稳态。时空表达模式分析发现，PHPP1在水稻幼苗中呈组成型表达，其编码蛋白定位于细胞核、细胞质以及内质网。虽然该基因的转录水平并不相应外界供磷水平变化，但其编码的蛋白受缺磷诱导。通过进一步分析，我们发现缺磷增强PHPP1蛋白的稳定性是缺磷诱导该蛋白积累的原因。在缺磷条件下，E2泛素结合酶PHO2的蛋白水平会降低，我们发现在供磷条件下PHO2能够与PHPP1互作并降解后者。因此，在本项目的支持下，我们鉴定了一条调控水稻磷素吸收的新通路，即PHO2-PHPP1-PHT1，该通路的鉴定可为水稻磷素养分高效吸收及利用奠定基础。