Precisely full length, circularizable, complementary RNA: an infectious form of potato spindle tuber viroid.
The replication of many viral and subviral pathogens as well as the amplification of certain cellular genes proceeds via a rolling circle mechanism. For potato spindle tuber (PSTVd) and related viroids, the possible role of a circular (-)strand RNA as a template for synthesis of (+)strand progeny is unclear. Infected plants appear to contain only multimeric linear (-)strand RNAs, and attempts to initiate infection with multimeric (-)PSTVd RNAs generally have failed. To examine critically the infectivity of monomeric (-)strand viroid RNAs, we have developed a ribozyme-based expression system for the production of precisely full length (-)strand RNAs whose termini are capable of undergoing facile circularization in vitro. Mechanical inoculation of tomato seedlings with electrophoretically purified (-)PSTVd RNA led to a small fraction of plants becoming infected whereas parallel assays with an analogous tomato planta macho viroid (-)RNA resulted in a much larger fraction of infected plants. Ribozyme-mediated production of (-)PSTVd RNA in transgenic plants led to the appearance of monomeric circular (-)PSTVd RNA and large amounts of (+)PSTVd progeny. No monomeric circular (-)PSTVd RNA could be detected in naturally infected plants by using either ribonuclease protection or electrophoresis under partially denaturing conditions. Although not a component of the normal replicative pathway, precisely full length (-)PSTVd RNA appears to contain all of the structural and regulatory elements necessary for initiation of viroid replication.
Feldstein
P A
PA
Plant Biology Department, University of Maryland, College Park, MD 20742, USA.
Hu
Y
Y
Owens
R A
RA
D001483:Base Sequence; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics*; D011198:Solanum tuberosum / Q000821:virology*; D014772:Viroids / Q000502:physiology*; D014779:Virus Replication
D012367:RNA, Viral