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  • 學位論文

植物賀爾蒙離層素對於柑橘鱗砧類病毒於番茄上病程進展之影響

Pathogenic effects of plant hormone Abscisic acid on Citrus exocortis viroid infected tomato plants

指導教授 : 沈湯龍
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摘要


類病毒為裸露的單股環狀RNA分子,大小約為250-400個核酸,且不轉譯任何蛋白質。類病毒是目前已知最小的植物病原且能感染多種作物造成嚴重的經濟損失。柑桔鱗砧類病毒(Citrus exocortis viroid, CEVd)為主要感染柑橘的類病毒,除了柑橘之外尚能感染番茄、馬鈴薯等植物。然而,柑橘鱗砧類病毒在造成植物病害發生的致病機制尚不明瞭。在先前的研究中發現當Rutgers品系的番茄受到柑橘鱗砧類病毒感染的番茄會表現出嚴重的葉片向下捲曲、葉片扭曲無法伸展與矮化等嚴重病徵。而先前的轉錄體(transcriptome)分析中,在柑橘鱗砧類病毒感染的番茄其離層素生合成的相關基因組有增加表現的情形。離層素(abscisic acid, ABA)在植物中主要參與種子發育與休眠、葉片生長、老化、防禦或是外在壓力耐受性相關的生理反應。因此,我們為柑橘鱗砧類病毒造成寄主植物葉片明顯的病徵可能與離層素表面失調有關。故本研究的目的在於探討柑橘鱗砧類病毒的病程發展與離層素之間的關係。首先,利用LC-MS/MS測定感病番茄中離層素的含量,我們發現離層素含量比較於健康植株有所改變。接著利用qPCR測定離層素生合成與代謝相關基因的表現量與ELISA assay測定離層素含量,發現隨著病程發展離層素的相關生合成基因與含量有皆隨著病徵發展呈現上升的趨勢。最後,在分別對已感染柑桔鱗砧類病毒的番茄處理離層素抑制劑fluridone或處理外源離層素,觀察病程的發展受到離層素的影響,進一步確認這兩者之間的關係。希望能提供另一種對於柑桔鱗砧類病毒病害管理的策略。

並列摘要


Viroids are small, circular and single-stranded RNAs which do not encode any protein. Known as the smallest pathogens, viroids are capable of infecting varied crops and result in crop yield reduction. Citrus exocortis viroid (CEVd) is the main viroid pathogen in the citrus industry; however, it can still infect other crops, such as tomatoes and potatoes. Upon infection a susceptible tomato cultivar, “Rutgers”, showed severe symptoms, such as epinasty, leaf distortion and stunting. Our previous transcriptome analysis of CEVd-infected tomato showed an up-regulated gene set involved in the abscisic acid (ABA) biosynthesis which is known as a defense-related phytohormone. In addition, ABA also plays a key role in seed development, seed dormancy, leaf formation and expansion and stress adaption. Nevertheless, the mechanism of viroids-induced pathogenesis/symptoms remained unknown. Here, we hypothesized that CEVd causing ABA homeostasis disorder may contribute to the development of pathogenic leaves. Firstly, utilizing LC/MS/MS analysis, we observed that the level of ABA content in infected tomato was higher compared to that of mock control. Consistently, we also found that there was an increase of the ABA biosynthetic gene sets during the progression of CEVd-mediated pathogenesis. Furthermore, while treated with fluridone, an ABA synthesis inhibitor, and exogenous ABA, the influence of the symptoms and pathogenesis of CEVd were apparently detected. As a result, ABA deficiency appears to increase either CEVd replication, whereas administration of exogenous ABA enabled to reduce CEVd replication. In conclusion, this study provided the first evidence for ABA involved in CEVd pathogenesis.

參考文獻


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