| Summary: | 碩士 === 國立臺灣大學 === 植物病理與微生物學研究所 === 105 === 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.
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