Study On Intermolecular And Intramolecular Recombinants Of Viroid

Viroid research confirmed inter and intra viroid RNA recombination. Since recombination contributes to the evolution and pathogenicity of viroid RNA, study on intermolecular and intramolecular recombinants of viroid RNA is significance to the research in recombinant evolution mechanism and pathogenicity of viroids. This work focused on the intermolecular recombinants of Coleviroids and an intramolecular recombinant (HSVd D-15) of Hostuviroids.1.Coleus blumei is foliage herbaceous plant which is extensively cultivated in the world. Up to now, four kinds of viroid were found infect coleus blumei, Coleus blumei viroid 1-4 (CbVd-1-4), and their intermolecular recombination have been reported. While studing viroid infection in the coleus blumei cultivated in China, we found two new viroids. We confirmed these two viroids were new species of genus Coleviroid, based on the results of sequencing, secondary structure prediction, sequence analysis and bio-indexing, and tentatively named them as CbVd-5 and CbVd-6.CbVd-5 has 66% sequence identity at the highest with the known viroid species, and shared the central conserved region of genus Coleviroid. Two terminal sequences highly conserved among some members of the genus were also found. We speculated those conserved sequence may play an important role on the replication and evolution of this viroid.CbVd-6 shares homologous sequences with the left part of CbVd-3 and the right part of CbVd-5. The discovery of this viroid proved efficient restructuring of genus Coleviroids. It may be of great significance to future research in viroid recombination mechanism.2. HSVd D-15 is the first reported HSVd intramolecular recombinant in the world which was discovered by our laboratory. In position 244-245, it has a 15nt repeat of position 230-244, compared with nomal HSVd. To examine it's infectivity, we constructed clones which contained multiple units of HSVd cDNA and HSVd D-15 cDNA and detected their infectivity on the indicator plant Cucumis sativus L Suyo. HSVd infection was found only in the plants inoculated with multiple units of HSVd cDNAs clone, but not in the plants inoculated with HSVd D-15 cDNAs dimer clone. The infectivity of HSVd D-15 should be further confirmed using improved inoculation method or inoculated it onto viroid free plums. Constructed clone of HSVd D-15 cDNA dimer has provided foundation to the research of HSVd D-15 infectivity on the original host plum.Three CbVd-5 (FJ151370-151372) and two CbVd-6 (FJ615418-615419) sequences were deposited into GenBank.