植物水通道蛋白结构与功能及其识别与转导水稻黄单胞菌Hpa1信号的机制

 植物水通道蛋白PIP不仅担负细胞间或细胞内外水分子输导的基本功能，还参与植物-微生物互作与植物防卫反应，这种双重功能的调控机制目前还不清楚。水稻OsPIP1;2和拟南芥AtPIP1;4可以与水稻黄单胞III型泌出蛋白Hpa1互作，Hpa1定位于植物细胞的质外体，诱导过氧化氢在质外体产生及向原生质转运，进而影响植物防卫反应与对病原细菌的抗性。根据植物水通道蛋白拓扑结构与病原细菌Ⅲ型分泌系统工作模型，水稻OsPIP1;2与Hpa1互作的功能域是互作发生的分子基础。互作引发信号转导，调控过氧化氢信号从植物细胞的质外体向原生质转运与植物防卫反应。由于Hpa1对Ⅲ效应蛋白来说具有转位子的功能特征，OsPIP1;2-Hpa1还可能对水稻黄单胞菌Ⅲ型效应蛋白从细菌细胞向植物细胞转运发生调控作用。围绕这些设想进行研究，可以深入阐释水稻-黄单胞菌互作机制，同时为植物水通道蛋白功能调控提供新的见解。

Plant aquaporins: structure meets function as associating with sensing of Xanthomonas oryzae Hpa1 and subsequent signal transduction

Plant aquaporin proteins basically mediate water transport through cell membranes, and also affect plant-microbe interactions and plant defense responses. Molecular mechanisms that underlie the dual function are unclear. Recently, the rice and Arabidopsis aquaporins OsPIP1; 2 and AtPIP1; 4 interact with Hpa1, a protein secreted by type Ⅲ pathway in Xanthomonas oryzae pathovars oryzae and oryzicola, which cause bacterial blight disaese and bacterial leaf streak disease of rice, respectively have been determined. When applied to plants or produced in transgenic plants, Hpa1 localizes to the apoplast and induces hydrogen peroxide generation in the same cellular location. The generation of hydrogen peroxide is dependent on the NADPH oxidase located at the plasma membrane. In response to Hpa1, moreover, the apoplastic hydrogen peroxide translocates to the cytoplasm with subcequent effects of enhancing plant defense responses to bacterial pathogens. According to established models in regard to the topological structure of aquaporins, the performance of bacterial type Ⅲ secretion, and subcellular trafficking of hydrogen peroxide in plants, it is necessary to identify the functional domain for OsPIP1; 2 interacting with Hpa1, and elucidate molecular features and structural basis of the OsPIP1; 2-Hpa1 interaction. Signal transduction triggered by the molecular interaction may be linked with the role of OsPIP1; 2-Hpa1 interaction in modulating translocation of apoplastic hydrogen peroxide to the cytoplasm, thus connecting the signal translocation with defense responses in rice. The OsPIP1; 2-Hpa1 interaction may also play a role in facilitating the translocation of X. oryzae type Ⅲ effector proteins from the bacterial cell to the plant cell because Hpa1 has been suggested as a candidate of tyep-Ⅲ effector translocators. With this hypothesis, studies are to further reveal regulatory mechanisms of plant-pathogen interactions, offerring a significant extension of aquaporins’ functions over what we have known up to date.