抗坏血酸过氧化物酶Zm-APX在玉米免疫防御反应中的功能及分子机制研究

Maize disease is one of the main factors that affect the yield and quality of maize. Study of maize immunology will promote capacity of maize immunity, and solve maize disease. Ascorbate peroxidase（APX）is one of the key enzyme meant for metabolizing stress-provoked reactive oxygen species (ROS; such as H2O2) and controlling their potential impacts on cellular metabolism and functions. Our preliminary results suggest that APX may play an important immunological function in maize. Based on our previous research work, this project aims to study the function and molecular mechanism of Zm-APX in maize through disciplinary pathway. The following experiments will contribute to obtain our research target: (1) Study the effects of pathogen associated molecular patterns and defense related phytohormone on Zm-APX through gene and protein level investigation. This will explore the role of Zm-APX in the immune response of maize. (2) Based on the overexpression and mutant lines of Zm-APX, which we have got in our previous experiments, examine the immune response parameters and disease resistance of maize. This will further confirm the function of Zm-APX. (3) Transgenic and mutant maize lines will be used for yeast two hybrid system, co-immunoprecipitation assay and proteomic analysis, which will be conducted to investigate the interaction and signal network of Zm- APX. These results will clarify the functional mechanism of Zm- APX in the immune response. Conduction of this project will further reveal the function and mechanism of ascorbate peroxidase in plant. Meanwhile, this project is of great significance in the field of maize immunology.

病害是影响玉米产量和质量的主要因素之一，开展玉米免疫学研究，从而提高玉米自身的免疫力，是从根本上解决这一问题的重要途径。抗坏血酸过氧化物酶（APX）是植物抗氧化防御系统中的关键酶，我们前期的研究工作揭示了Zm-APX在玉米免疫防御反应中发挥着重要的功能，本项目在前期研究工作的基础上主要开展以下研究内容：（1）分别从基因和蛋白水平研究病原相关分子模式、植物免疫防御激素对Zm-APX的影响，探索其在玉米免疫防御反应中的调控作用；（2）利用已经得到的玉米转基因株系和突变体材料，分别从正反两方面分析免疫反应参数、抗病表型以及病理参数的变化来证实Zm-APX的功能；（3）利用酵母双杂交、免疫共沉淀以及植物蛋白质组学等技术，研究Zm-APX的相互作用蛋白及所在信号网络关系，阐明Zm-APX的免疫防御作用机制。本项目可为进一步揭示植物APX的功能及作用机制奠定基础，同时对推动作物免疫学研究有着重要意义。

玉米小斑病(SCLB)是由玉蜀黍平脐蠕孢菌(Bipolaris maydis)引起的一种严重危害玉米生产的病害。然而，目前仅鉴定到一个小斑病不完全抗性基因，因此，鉴定新的小斑病抗性相关基因具有重要意义。在本研究中，我们利用比较蛋白质组学鉴定到258个蛋白在玉米响应玉蜀黍平脐蠕孢菌侵染过程中差异表达。这些差异表达蛋白质包括一个位于先前鉴定到的与SCLB抗性相关的QTL区间内的抗坏血酸过氧化物酶（ZmAPX1）。ZmAPX1过表达降低了过氧化氢的积累，增强了对玉米小斑病的抗性。在ZmAPX1过表达的植物中，JA含量和JA生物合成以及应答基因的转录水平均增加，而Zmapx1突变体则表现出相反的效果。进一步研究表明：低水平的H2O2促进JA的积累，从而增强了SCLB抗性。这些结果证明了ZmAPX1通过降低H2O2的积累和激活JA介导的防御信号通路来正向调节SC1B的抗性。本研究证明了ZmAPX1可以作为一个潜在的小斑病抗性基因。另外，本研究对阐明植物APX的功能也具有一定的价值。