Skip to main content
ARS Home » Research » Publications at this Location » Publication #72571
Title: PRECISELY-FULL-LENGTH, CIRCULARIZABLE, COMPLEMENTARY RNA- A NOVEL INFECTIOUS FORM OF POTATO SPINDLE TUBER VIROID

Author
item FELDSTEIN, P - UNIV OF MD COLLEGE PK MD
item HU, Y - UNIV OF MD COLLEGE PK MD
item Owens, Robert

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Viroids are the smallest known agents of infectious disease--small, highly structured RNA molecules which lack both a protein capsid and detectable mRNA activity. For potato spindle tuber (PSTVd) and related viroids, the possible role of a circular complementary RNA as a template for progeny synthesis is unclear. We have developed a method to synthesize precisely-full-length RNA molecules complementary to PSTVd, and mechanical inoculation of tomato seedlings with such RNAs resulted in variable rates of infection. In transgenic plants expressing such complementary RNA, the RNA was circularized, and large amounts of PSTVd progeny were produced. This phenomenon appears to represent a novel pathway for initiating viroid replication, and the ability to produce large amounts of precisely-full-length viroid RNA of either polarity will greatly facilitate studies of viroid replication. Fundamental information of this sort is of greatest interest to researchers studying host-pathogen interactions at the molecular level, for it suggests new strategies by which it may be possible to create durable resistance to viroid infection/disease for ultimate benefit to farmers and consumers.

Technical Abstract: The replication of many viral and subviral pathogens as well as the amplication of certain host genes proceeds via a rolling circle mechanism. For potato spindle tuber (PSTVd) and related viroids, the possible role of a circular complementary (-)PSTVd RNA as template for synthesis of (+)strand progeny is unclear. Infected plant tissue contains multimeric linear (-)PSTVd RNAs, but previous attempts to initiate infection with multimetric (-)RNA transcripts have generally failed. To critically examine the infectivity of monomeric (-)RNAs, we have developed a ribozyme-based expression system for the production of precisely-full-length (-)PSTVd and (-)tomato planta macho viroid (TPMVd) RNAs whose termini are capable of undergoing facile circularization in vitro. Mechanical inoculation of tomato seedlings with electrophoretically purified (-)PSTVd RNA led to a low (but reproducible) rate of infection; parallel assays with (-)TPMVd RNA resulted in much higher rates of infection. Ribozyme-mediated production of (-)PSTVd RNA in transgenic Nicotiana benthamiana plants led to the accumulation of detectable levels of monomeric circular (-)PSTVd RNA and the appearance of large amounts (+)PSTVd progeny. The infectious nature of precisely-full-length (-)PSTVd RNA appears to represent a novel pathway for initiating viroid replication rather than the entry of a circularized (-)RNA into the normal replicative pathway.