當植物遭受到病原菌攻擊時，會啟動相關的防禦機制阻止病菌的入侵，例如刺激植株產生過氧化物(reactive oxygen species, ROS)。多數植株在感染的初期可以有效阻止病菌入侵，一旦植株無法阻擋病菌快速擴散，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。首先藉由比較植株在感染後基因表現的差異，找出參與在此過程中的基因，先期的實驗已利用抑制性扣減雜交法(suppression
subtractive hybridization, SSH)找出感染軟腐菌24小時後所誘發的蝴蝶蘭基因並依據其功能分為八群。其中轉錄因子PabZIP與PaWRKY在目前的研究已知與植物抗病以及逆境有關，由於轉錄因子可調控其他基因之表現，因此研究轉錄因子基因功能有助於了解抗病機制；除了已知與防禦以及逆境相關的基因外， 在SSH 分析可以發現參與長鏈脂肪碳合成的酵素trans-2-enoyl-CoA-reductase(ECR)基因表現在感染軟腐菌時會被誘導，而該基因在之前的研究並未發現與抗病有關。為了進一步了解蝴蝶蘭與軟腐菌的交互關係，因此選擇分析PabZIP、PaWRKY、與PaECR基因功能以及在此過程中所扮演的角色。首先以RT-PCR確認利用確認基因表現，發現上述基因在感染後六小時表現量都會上升，且於感染後二十四小時仍持續表現。為了解PabZIP、PaERKY、與PaECR是否與植株的抗病能力相關，因此利用病毒誘導基因靜默法(virus-induced gene silencing, VIGS)抑制蝴蝶蘭內生性基因的表現，發現若抑制PaECR表現將導致植株抗病降低。因此，藉由分析SSH資料庫內基因表現以及利用病毒誘導基因靜默法可幫助了解基因在植株抗病時的功能，透過更多基因的分析有助於在分子層次上了解蝴蝶蘭感染軟腐菌的關係，或許不久即可培育出具有抗病力的植株。

Plants respond to pathogen attack by activating arrays of inducible defense mechanisms.
A previous study using suppression subtractive hybridization (SSH) strategy was
applied in search for genes that were induced after infection of Phalaenopsis
orchids by a bacterial pathogen, Erwinia chrysanthemi. As a result, a pool of 73 unique
mRNA transcripts form Erwinia-infected orchids exhibited different expression profiles
when compared to healthy plants. Among these, two candidate genes showed early
responsiveness to Erwinia infection and were subsequently selected for functional
analysis in this study. The first one is a enoyl-CoA reductase gene (PaECR), which
encodes a enzyme that catalyzes the last step of very-long-chain fatty acids elongation.
The other is a gene encoding a putative basic-leucine zipper transcription factor, termed
PabZIP. Semiquantative RT-PCR analysis of gene expression showed that the
steady-state level of the PaECR transcripts increased 6 hours (hrs) post-inoculation and
remained elevated through 24 hrs. Furthermore, the gene expression of PabZIP was
induced at 6 hrs after challenge with Erwinia. These genes were both strongly induced
by Erwinia infection, confirming the SSH-based results. To understand the function of
PaECR and PabZIP genes in orchid plants, loss-of-function study was performed by
virus-induced gene silencing (VIGS) of the PaECR and PabZIP gene, respectively.
Interestingly, the results indicated that silencing of PaECR in orchid plants enhanced
the susceptibility to Erwinia. In summary, the study suggests that PaECR may play
important roles in resistance to Erwinia. Further characterization and functional analysis
of these genes will gain more insight into the molecular mechanisms underlying
orchid-Erwinia interactions, which may lead to improvement of orchid agriculture.

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