植物無法像動物一樣利用移動的方式躲避病原菌或其他生物的攻擊而選擇適合的環境生存，因此當植物遭受病原菌攻擊時，會啟動相關防禦機制阻止病原菌的入侵，一旦植株無法阻擋病原菌快速擴散，即會造成植株的死亡。軟腐病菌 (Erwinia chrysanthemi)是目前台灣蘭園中常見的細菌性病原菌，易造成蘭園大規模的感染，本篇研究主要探討蝴蝶蘭與軟腐菌之間的交互關係。在先期的實驗中利用抑制性扣減雜交法 (suppression subtractive hybridization, SSH)找出感染軟腐菌24小時所誘發的蝴蝶蘭基因。其中轉錄因子在近年來的研究中多次被提及與植物的免疫調控路徑有關，包括對生物及非生物逆境、老化、及次級代謝物的合成等。在本篇的研究中除了探討蘭花中受病菌誘發的轉錄因子PabZIP與PaWRKY之外，也對參與長鏈脂肪碳合成的酵素trans-2-enoyl-CoA-reductase (ECR)是否參與抗病亦有興趣。首先，以軟腐病菌感染蝴蝶蘭的葉子或處理其他不同誘導物，植株體內的PabZIP、PaWRKY及PaECR基因表現量會有顯著改變。接著，利用酵母菌系統可以證實PabZIP及PaWRKY蛋白質具有轉錄因子活性及功能。為了解PabZIP、PaWRKY及PaECR是否與蝴蝶蘭的抗病能力有關及其在抗病上扮演的角色，將這三個蛋白質分別大量表現在阿拉伯芥中，以軟腐病菌感染轉殖株小苗，結果顯示大量表現PabZIP時，會造成轉殖株小苗比野生型抗軟腐菌；至於大量表現PaWRKY及PaECR，在小苗抗病能力上與野生型沒有差異。因此，藉由上述的結果來看，當軟腐病菌感染蝴蝶蘭時，會造成多個基因的表現受到改變，其中PabZIP扮演著正調控的角色，可以阻檔病原菌的入侵。此外，我們也發現大量表現PabZIP轉殖株對鹽的耐受度比野生型高，顯示PabZIP在蝴蝶蘭可能同時參與調控生物及非生物性逆境，本研究對於蘭花轉錄因子PabZIP及PaWRKY的功能性探討將有助於蘭花在軟腐病害上的防治。

Plants respond to pathogens by regulating a network of signaling pathways that fine-tune transcriptional activation of defense-related genes. The suppression subtractive hybridization strategy was applied in search for genes that were induced after infection of P. amabilis (orchids) by a necrotrophic bacterial pathogen, Erwinia chrysanthemi. As a result, a pool of 73 unique mRNA transcripts from E. chrysanthemi-infected orchids exhibited different expression profiles when compared to healthy plants. Among these, two genes encoding basic leucine zipper and WRKY transcription factors (referred to as PabZIP and PaWRKY, respectively) were found to be rapidly induced in orchid leaves by E. chrysanthemi infection. Translational fusion of PabZIP and PaWRKY with green fluorescence protein revealed the subcellular localization of the protein in the nucleus. To investigate the function of the two transcription factors, transgenic Arabidopsis plants overexpressing PabZIP and PaWRKY were generated. Interestingly, constitutive expression of PabZIP in Arabidopsis induced the activation of various defense-related gene expression, including a jasmonate-responsive gene plant defensin 1.2 (PDF1.2). The induced expression of PDF1.2 gene was not observed in transgenic Arabidopsis plants overexpressing PaWRKY. Subsequently, functional analysis was performed to understand if the PabZIP contributed to resistance to E. chrysanthemi. It was found that transgenic Arabidopsis plants overexpressing PabZIP exhibited reduced levels of necrosis symptoms and cell death, indicating the role of PabZIP in resistance to E. chrysanthemi. Furthermore, expression of the PabZIP gene in transgenic Arabidopsis plants also contributed tolerance to high salinity stress. In summary, the results suggested that the PabZIP may regulate complex transcriptional networks such as defense-related genes, which in turn conferred resistance to E. chrysanthemi and tolerance to salinity stress. The modification of transcriptional control by regulatory transcription factors provides a useful strategy for improving tolerance to biotic and abiotic stresses in plants.

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