| Budget Amount *help |
¥16,000,000 (Direct Cost: ¥16,000,000)
Fiscal Year 2004: ¥4,600,000 (Direct Cost: ¥4,600,000)
Fiscal Year 2003: ¥11,400,000 (Direct Cost: ¥11,400,000)
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| Research Abstract |
(1)Cassia yellow blotch bromovirus(CYBV) was shown to infect systemically and efficiently a model plant species, Arabidopsis thaliana, as we recently reported for another bromovirus, Spring beauty latent bromovirus(SBLV). CYBV and SBLV showed different infectivities in some accessions of A.thaliana. Full-length cDNA clones of CYBV genomic RNAs were constructed, from which infectious in vitro transcripts can be transcribed. (2)Symptom development was examined in A.thaliana accessions infected with SBLV. Several accessions including S96 were sensitive to SBLV infection, while the other accessions including Col-0 were symptomless or developed mild symptoms. Genetic study suggested that the symptom phenotype of S96 is controlled by a single semidominant locus. We have designated this locus SSB1. Infectivity of SBLV in plants and protoplasts were comparable between Col-0 and S96, indicating that variation of symptom phenotype was not due to the different infectivity of SBLV. By using genetic markers, SSB1 was mapped between CAT2 and nga1107 on chromosome IV. Genetic analyses suggest that symptom development in A.thaliana controlled by SSB1 is dependent on salicylic acid signaling and ethylene signaling. (3)Brome mosaic bromovirus(BMV) shows limited infection in A.thaliana, while SBLV efficiently infects it. In a screening of Arabidopsis mutants with altered defense responses, BMV was found to infect A.thaliana systemically and efficiently by the cpr5 mutations, which have been known to constitutively express systemic acquired resistance(SAR). Double and triple mutants of cpr5 with these pathways disrupted still allowed BMV to infect A.thaliana efficiently, suggesting that cpr5 mutations enhance BMV multiplication by the mechanism independent of that to confer SAR. Even in protoplasts, multiplication ability of BMV was lower than that of SBLV and was enhanced by the cpr5 mutations.
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