Achloroplastic RNA polymerase resistant to tagetitoxin is involved in replication of avocado sunblotch viroid

Author(s): Navarro JA, Vera A, Flores R


Avocado sunblotch viroid (ASBVd), the type species of the family Avsunviroidae, replicates and accumulates in the chloroplast. Two main chloroplastic RNA polymerases have been described: the plastid-encoded polymerase (PEP) with a multisubunit structure similar to the Escherichia coli enzyme and a single-unit nuclear-encoded polymerase (NEP) resembling phage RNA polymerases. On a different basis, sensitivity to tagetitoxin, two major RNA polymerase activities, tagetitoxin sensitive (TS) and resistant (TR), have been found in plastids. The most plausible candidates for the TS and TR RNA polymerases are PEP and NEP, respectively. To gain an insight into the enzymology of the polymerization of ASBVd strands, purified chloroplast preparations from ASBVd-infected leaves were assayed for their in vitro ability to transcribe ASBVd RNAs together with some representative genes (psbA, 16SrDNA, accD, and rpoB) of the three classes of chloroplastic genes according to their promoter structure. High concentrations of alpha-amanitin had no effect on gene or on viroid transcription, but tagetitoxin (5-10 microM) prevented transcription of all these genes without affecting synthesis of ASBVd strands; only at higher tagetitoxin concentrations (50-100 microM) was a 25% inhibition observed. These results suggest that NEP is the RNA polymerase required in ASBVd replication, although the participation of another TR RNA polymerase from the chloroplast cannot be excluded.

Similar Articles

Potato spindle tuber "virus"

Author(s): Diener TO

Inhibition of potato spindle tuber viroid (PSTVd) infection with DNA oligonucleotides

Author(s): Matousek J, Trnena L, Arnold L, Dedic P, Rakousky S, et al.

Behavior of a hammerhead ribozyme in aqueous solution at medium to high temperatures

Author(s): El-Murr N, Maurel MC, Rihova M, Vergne J, Hervé G, et al.

The revised classification of eukaryotes

Author(s): Adl SM, Simpson AG, Lane CE, Lukes J, Bass D, et al.

Improving the coverage of the cyanobacterial phylum using diversity-driven genome sequencing

Author(s): Shih PM, Wu D, Latifi A, Axen SD, Fewer DP, et al.

Accurate strand-specific quantification of viral RNA

Author(s): Plaskon NE, Adelman ZN, Myles KM

Self-cleavage of plus and minus RNA transcripts of avocado sunblotch viroid

Author(s): Hutchins CJ, Rathjen PD, Forster AC, Symons RH