| Budget Amount *help |
¥7,800,000 (Direct Cost: ¥7,800,000)
Fiscal Year 2006: ¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2005: ¥2,400,000 (Direct Cost: ¥2,400,000)
Fiscal Year 2004: ¥3,200,000 (Direct Cost: ¥3,200,000)
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| Research Abstract |
Upon infection to plant hosts, plant viruses cause vast varieties of disease symptoms including mosaic, yellows, chlorosis, ring spot, mottle, and so on. Molecular mechanisms underlying expression of these symptoms, however, have scarcely been uncovered. In this project, I studied the mechanism using two species of plant viruses belonging to Genus Potexvirus. Potato virus X (PVX) and Plantago asiatica mosaic virus (PIAMV). The strains OS and BH of PVX cause ring spot and mosaic, respectively, upon infection to tobacco plant (Nicotiana tabacum). Construction of chimeric genomes of the two strains and site-directied mutagenesis of the viral genomes revealed that the 58th nucleotide of the 5 prime untranslated region of the viral genome was responsible for determination of distinct symptoms. Distribution of viral RNA of each PVX strain, as well as transcription of host defense genes, was monitored in the infected leaves by in situ hybridization technique. In the area of ring spot, some plant genes related to the hypersensitive response (HR) such as pathogenesis-related protein 1a (PR-1a) were expressed. Viral RNA was found both inside and outside of the area of ring spot. These data suggest that the ring spot symptom caused by strain OS is a result of induced HR-like plant cell death yet unsuccessful in restricting the spread of the virus. The strains Li1 and Li6 of PlAMV cause systemic necrosis and mosaic, respectively, upon infection to Nicotiana benthamiana plants. Molecular analysis revealed that the 1154th amino acid of the viral replicase encoded in the PlAMV genome was responsible for the symptom determination. HR-like response was also observed in plants infected with the strain Li1. These data support the idea that some symptoms such as ring spot and systemic necrosis are caused by host plant responses which tried to restrict viral spread.
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