Characterization of the Different Electrophoretic Forms of the Cadang-Cadang Viroid

Abstract

SUMMARYThe relationship between symptom development and changes in the fast and slow electrophoretic forms of the two cadang-cadang disease-associated RNAs (ccRNA-1 and ccRNA-2) has been examined. The fast form of each is present in trees for up to 2 years before the appearance of symptoms, indicating an incubation period of about 2 years. Trees showing the first symptoms (on the nuts) contain only the fast form of the ccRNAs; the development of leaf symptoms coincides with the first detection of the slow form. After this time, both slow and fast forms are found in the newly developing fronds for the next 9 to 12 months but then, as symptoms develop, new fronds contain only the slow form. Therefore, at later stages of disease, only the slow form can be detected in all fronds. The fast form of ccRNA-1 and/or ccRNA-2 therefore appears to be the infectious form in nature. The number of nucleotides in the four ccRNAs as determined by polyacrylamide gel electrophoresis under denaturing conditions are: ccRNA-I fast, 250; ccRNA-1 slow, 300; ccRNA-2 fast, 500; ccRNA-2 slow, 600. On the basis of two-dimensional fingerprints of ribonuclease A and T1 digests of the four ccRNAs, it was concluded that the ccRNAs are composed of repeated sequences of ccRNA-I fast, and each of the ccRNA-2 forms is a dimer of the respective ccRNA-1 form.

Comparison of multimeric plus and minus forms of viroids and virusoids

“…3B, track 5, and that the two types of minus pattern obtained reflect variable b r e a k d o w n of nucleic acids during the p r e p a r a t i o n of nucleic acid extracts from different leaf samples. A similar series of minus species has been observed with P S T V and CEV (2, 3, 4, 27, Plus and minus sequences of CCC V E x t r a c t s f r o m three different palms at the early, i n t e r m e d i a t e and late stages of c a d a n g c a d a n g disease (16,17,26) were e x a m i n e d for plus and m i n u s sequences using full-length 3 2 p -R N A probes. N o rt h e r n analysis s h o w e d a m u l t i m e r i c series of plus species (Fig.…”

“…Grosse Lisse), VTMoV, SNMV (12,13,15,31) and LTSV-N (18,19,43) in Nicotiana clevelandii, and LTSV-A (18,19,43) in Chenopodium quinoa. Partially purified extracts of CCCVinfected coconut palm fronds (17,26) were kindly provided by Lita Imperial and Judith Rodriguez, Albay Research Center, Philippines. Circular forms of ASBV, CEV and CCCV (fast and slow forms) were purified from nucleic acid extracts of infected plants by two-step polyacrylamide gel electrophoresis (16,17,26,30,39,44).…”

“…Partially purified extracts of CCCVinfected coconut palm fronds (17,26) were kindly provided by Lita Imperial and Judith Rodriguez, Albay Research Center, Philippines. Circular forms of ASBV, CEV and CCCV (fast and slow forms) were purified from nucleic acid extracts of infected plants by two-step polyacrylamide gel electrophoresis (16,17,26,30,39,44). Isolation of virus from VTMoV, SNMV and LTSV-infected leaf tissue, viral RNA extraction and virusoid purification were as described (12,13,19,31,43).…”

“…The slow electrophoretic forms of CCCV involving a duplication at the right hand end of the molecule and which arise during infection (16,17,26) indicate RNA rearrangement, the mechanism of which is unknown. Further, the X-bands found associated with the plus forms of ASBV, SNMV RNA 2 and VTMoV RNA 2 and with the minus forms of CEV and ASBV may be remnants of RNA rearrangements associated with replication.…”

Interactions between Citrus Exocortis and Potato Spindle Tuber Viroids in Plants of <i>Gynura aurantiaca</i> and <i>Lycopersicon esculentum</i>

“…Coconut cadang-cadang viroid (CCCV) has different molecular forms: CC1S, a small (S) monomeric form of 246-247 nucleotide resi dues, and CC1L, which is CC1S containing a reiterated sequence of 41-55 residues at the right-hand end of the molecule, producing a large (L) form [Randles, 1987]. CC1S is de tected in the early stages of the disease and coexists with CC1L in the medium stages, while CC1L is the form that persists in the late stages [Imperial et al, 1981: Mohamed et al, 1982, These observtions could be explained by assuming that CC1L, due to the sequence reiteration, would have a higher affinity than CCIS for a limiting host factor, out-compet ing this latter form in the course of the dis ease.…”