信号肽类似序列对黄单胞菌Harpin蛋白——HpaXm转运的影响

Harpins can function as effector proteins to induce a systemic acquired resistance(SAR) on some nonhost plants. Several studies suggest that the Harpins secretion via type III secretion system.In our previous studies，we first described a novel harpin-like protein, HpaXm, from cotton leaf blight bacteria, Xanthomonas citri subsp. malvacearum，revealed a signal peptide-like sequence in its N-terminus. This suggests that there is probably a type II secretion process involved in the transport pathway of HpaXm. In this study, We intend to use the method of genetic and reverse genetic to demonstrate whether or not the signal peptide will affect the type three secretion process of HpaXm and the HpaXm can be secreted through other pathway except type III seretion system. And then，we are going to confirm the signal peptide of HpaXm using the known II secretory protein，and analyze the T3SS-independent translocation pathway of HpaXm in vivo and vitro by constructing mutant strains of Xanthomonas，deleting the key gene of the type two secretion device and the type three secretion device respectively and observing the secretion process of HpaXm in wild strain and various mutant strains. At last,we want to research the influence of signal peptide of HpaXm on its transportation and function by using transgenic plants. These results will help us further to understand the interaction of pathogen and plant, and the mechanism of plant defense response.

Harpin是一类能诱导抗病性的蛋白类激发子。目前公认Harpin由III 型分泌系统（T3SS）转运。但在前期研究中，我们从棉花角斑病菌首次鉴定了新Harpin类蛋白-HpaXm，二级结构预测显示HpaXm N端存在信号肽序列，暗示HpaXm也可能通过II型分泌系统（T2SS）转运。因此，我们以HpaXm为例，采用遗传学与反向遗传学的方法，研究信号肽是否影响HpaXm的III型泌出方式，利用已知II型分泌蛋白确定HpaXm的信号肽序列，构建黄单胞菌突变菌株，分别敲除T3SS和T2SS泌出通道的关键基因，在离体和活体条件下研究HpaXm不同突变体与其野生型菌株泌出方式，分析黄单胞菌中不依赖T3SS的HpaXm的转运途径；并利用植物转基因途径解析信号肽序列对HpaXm在植物体内转运功能的影响，为研究植物与病原菌互作及植物防卫反应机制提供科学依据。