Analysis of the viroid structural domains regulating viroid pathogenicity

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To Investigate the viroid structural domains regulating viroid pathogenicity, we have produced the recombinant cDNA clones pBS-CE/HS-TR,pBS-HS-CE-TR and pBS-CE/AS-TR by exchanging the terminal right (TR) domain amond HSVd, CEVd and TASVd. We focused our analysis mainly on the roles of the TR domains in the viroid pathogenisity.We have constructed the chimeric viroid cDNA clones described above using recombinant DNA techniques and PCR in the first year (1993). From the last quarters in the first year, we started the infectivity assays using the recombinant chimeric cDNA clones and found that,(1)the pBS-CE/HS-R and pBS-HS-CE-TR was infectious, and replicated stable in cucumber and tomoto,(2)but pBS-CE/AS-TR was nou infectious.Furthermore, we have accomplished the critical analysis on the pathogenicity of the infectious viroid chimeras (CE/HS-TR and HS/CE-TR), and revealed that TR domain was critical for the viroid replication or accumulation.Our results showed that,(1)the TR domain was exchangeable without loosing their viability between the different viroid group such as HSVd group and PSTVd group.(2)the TR domain regulates viroid pathogenicity via its replication and/or accumulation rates in the infected host plants.