- 學位論文
植物防禦素AtPDF1.1藉由鐵螯合防禦機制提高對細菌性軟腐病之抗性
The Arabidopsis defensin gene AtPDF1.1 mediates defense against Pectobacterium carotovorum subsp. carotovorum via an iron-withholding defense system
摘要
植物防禦素是一種富含半胱氨酸的小分子蛋白質，參與多種生物功能。其中，較多的研究是關於對抗植物病原菌，尤其是對於真菌類的病原菌。而對於細菌性病原菌之防禦機制的了解則相對較為稀少。本研究發現阿拉伯芥植物防禦素(AtPDF1.1)是一個具有鐵離子親和力的分泌性蛋白。在大量表現植物防禦素的轉殖植物，鐵離子會被聚集在細胞的質外體進而擾亂細胞的鐵離子分布。當阿拉伯芥感染細菌性軟腐病菌(Pectobacterium carotovorum subsp. carotovorum)，此植物防禦素會在感染葉與系統葉受到誘導而增加其表現量，並在轉殖植物中提高抗病耐受性。這些結果顯示植物防禦素參與抵抗細菌性軟腐病原菌的角色。藉由分析鐵恆定或缺乏和植物賀爾蒙相關基因的表現情形，發現葉片植物防禦素大量表現造成的鐵離子分布失去平衡會誘導缺鐵訊息，此缺鐵訊息會傳遞到根部進而活化乙烯合成與訊息傳遞相關基因的表現。活化的乙烯相關反應可能促使在系統葉上乙烯反應路徑的相關基因也跟著一起提高表現，而活化乙烯相關反應已被證實會增加對軟腐病菌的抗病性。總言之，我們的研究顯示：當阿拉伯芥感染細菌性軟腐病菌時，藉由提高植物防禦素在質外體的表達而造成一種鐵螯合防禦系統，而這機制可能就是植物防禦素參與對抗病原菌二次感染的生物功能。另一方面，當植物防禦素與病菌競爭可利用的鐵，也會直接地抑制病原菌生長與發病過程。本研究首先提出植物防禦素在對抗細菌性軟腐病菌所扮演的功能。
並列摘要
Plant defensins (PDFs) are cysteine-rich peptides that have a range of biological functions, including defense against fungal pathogens. However, little is known about their role in anti-bacterial defense systems. In this study, we showed that the protein encoded by ARABIDOPSIS THALIANA PLANT DEFENSIN TYPE 1.1 (AtPDF1.1) is a secreted protein that can chelate apoplastic iron. Transcripts of AtPDF1.1 were induced in both the infected and systemic non-infected leaves of Arabidopsis thaliana plants infected with the necrotrophic bacterium Pectobacterium carotovorum subsp. carotovorum (Pcc). Moreover, overexpression of AtPDF1.1 in A. thaliana led to enhanced tolerance to Pcc, suggesting its involvement in defense against bacteria. Expression analysis of genes associated with iron homeostasis/deficiency and hormone signaling indicated that the sequestration of iron by apoplastic AtPDF1.1 perturbs iron homeostasis in leaves and consequently activates an iron deficiency-mediated response in roots via the ethylene signaling pathway. This in turn triggers ethylene-mediated signaling in systemic leaves, which is involved in suppressing the infection of necrotrophic pathogens. These findings provide new insight into the key functions of plant defensins in limiting the infection by a phytopathogenic bacterium via an iron-deficiency-mediated defense response.