2010-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/698260摘要：群數感應 (quorum sensing) 是一種細菌與細菌個體或族群間透過訊號分子來感應族群密度，進而調控目標基因表現以適應環境的一種溝通方式。在植物病原菌 Pseudomonas syringae 中，有關群數感應的研究並不完整，僅知群數感應會影響P. syringae pv. syringae及 P. s. pv. tabaci 產生EPS 的能力、移動力及致病力；另外在P. s. pv. tomato (Pto)中的研究則是在群數感應上游的調控網絡上，對於群數感應是如何影響致病力的機制，其了解並不透徹。之前的研究指出，P. syringae的PsrA蛋白質除了會負調控群數感應基因之外，也可藉由調控第三型分泌系統來影響 P. s. pv. tomato 在植物中生長的適應力。另外，由動物病原菌的研究中發現，群數感應可調控第三型及第六型分泌系統 (包括整個分泌系統構造及其分泌之作用蛋白) 而影響其病原性及致病力。第三型分泌系統之重要性已在模式菌株P. s. pv. tomato strain DC3000 (Pto DC3000) 及其他重要植物病原菌中被證實；後者是否與植物病原菌之致病力有關，仍有待探討。因此本實驗將利用基因體早已被解序出來且研究頗多的模式植物病原菌 Pto DC3000，來探討群數感應對植物病原細菌第三型及第六型分泌系統的影響，以了解群數感應調控多種病原菌生理現象的分子機制。<br> Abstract: Quorum sensing is the ability of bacteria to communicate and coordinate certain behaviors and actions via signaling molecules. Bacteria can utilize this cell-to-cell communication to regulate gene expression according to the local concentration of the signaling molecules, called “autoinducers”. Researches in Pseudomonas syringae are incomplete. We know that quorum sensing is involved in exopolysaccharide production, motility, and virulence of Pseudomonas syringae pv. syringae and P. s. pv. tabaci. Furthermore, both AefR and PsrA are key regulators of quorum sensing systems in P. s. pv. syringae and P. s. pv. tomato, in which PsrA negatively regulates genes encoding the AHL synthase and the response regulator, and positively regulate epiphytic fitness via activation of type III secretion system (T3SS). However, the molecular mechanisms of how quorum sensing affects virulence activity of the phytopathogenic bacteria remain unclear. Studies in mammalian pathogens showed that quorum sensing controls pathogenicity and virulence activities via regulation of type III and type VI secretion loci. The importance of T3SS in pathogenicity and virulence is well-studied in phytopathogenic bacteria, but that of type VI secretion system (T6SS) needs to be elucidated. Therefore, a sequenced model bacterial pathogen, PtoDC3000, is chosen to study the effects of quorum sensing on T3SS and T6SS in order to understand the molecular mechanisms underlying the regulatory circuits of the quorum sensing phenomenon群數感應第三型分泌系統第六型分泌系統植物病原細菌分子機制quorum sensingtype III secretion system (TTSS)type VI secretion system(T6SS)Pseudomonas syringaemolecular mechanisms