Cytological and Molecular Biological Analyses of Mechanisms of Signal Recognition and Host Specificity at Incipient Infection Stage

白粉病分生孢子接触疏水性膜后立即释放胞外物质(ECM)。本研究证实小麦白粉菌、小麦白粉菌、白粉菌在寄主表面能释放细胞外基质。ECM有助于分生孢子的黏附和芽管萌发部位的确定。免疫电子显微镜和共聚焦显微镜观察表明，在分生孢子接触后30min内，物质通过ECM从分生孢子转移到寄主表皮，反之亦然。与大麦非病原菌B.g.tritici和E.pisi的ECM接触的大麦表皮细胞在接触分生孢子后6~7h内直接走向不可及，而接触B.g.hordei(大麦的病原菌)ECM的大麦表皮细胞在接触分生孢子后6~7h内既不通向也不通向不可及。这些结果表明，分生孢子与寄主细胞接触后，信号转导和寄主反应立即开始。燕麦酸奶杆菌在单子叶植物中的寄主范围很广，但单个菌株只能侵染一个或几个寄主物种。最近我们报道了不亲和品系引起的抗性反应，而亲和品系没有。我们还报道了该不亲和品系的鞭毛蛋白诱导的抗性反应。为了研究不亲和品系诱导水稻防御反应的机制以及鞭毛蛋白在这一防御反应中的作用，利用基因芯片技术对水稻进行了基因芯片分析。基因芯片分析表明，25个基因的诱导受不亲和鞭毛感知调控。我们还研究了不相容和相容鞭毛之间抗性反应的诱导特异性。用纯化的鞭毛蛋白和重组鞭毛蛋白诱导培养的水稻细胞产生抗性反应的分析表明，鞭毛蛋白的特异性参与了鞭毛蛋白的翻译后修饰。

Powdery mildew conidia were known to release extracellular materials (ECM)immediately after contact to hydrophobic membranes. In this study, Blumeria graminis hordei and B.g.tritici, Erysiphe pisi were confirmed to release ECM on host surfaces. ECM contributes to adhesion of conidia and determination of the emergence site of germtubes. Immuno electron and confocal microscopies revealed that materials were moved from conidia to host epidermis and vice versa via ECM within 30 min after conidial contact. Epidermal cells of barley that contacted ECM of B.g.tritici and E.pisi (both nonpathogens to barley) were directed towards inaccessibility within 6-7 h after conidial contact, while those that contacted ECM of B.g.hordei (pathogen to barley) were directed towards neither accessibility nor inaccessibility. These results show that signal transduction and host response initiate immediately after conidium-host cell contact. The host range of Acidovorax avenae is wide among monocotyledonous but individual strains can infect only one or a few host species. Recently we reported that incompatible strain of A.avenae caused the resistance response, but compatible strain did not. We also reported that the resistance response was induced by flagellin from the incompatible strain. To investigate the mechanism of rice defense response induced by the incompatible strain and the role of flagellin on this defense induction, rice cDNA microarray analysis was performed. The microarray analysis showed that induction of 25 genes was regulated by the incompatible flagellin perception. We also investigated induction specificity of resistant response between incompatible and compatible flagellins. Induction analysis of resistant response in cultured rice cells using purified flagellins and recombinant flagellins showed that the flagellin specificity is involved in the post-translational modification of flgaellins.