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Title: MUTATIONAL ANALYSIS OF A PUTATIVE TERTIARY STRUCTURAL ELEMENT IN THE LEFT TERMINAL DOMAIN OF POTATO SPINDLE TUBER VIROID

Author
item Owens, Robert
item Thompson, Susan

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2005
Publication Date: 2/23/2005
Citation: Owens, R.A., Thompson, S.M. 2005. Mutational analysis of a putative tertiary structural element in the left terminal domain of potato spindle tuber viroid. Journal of General Virology. 86:1835-1839.

Interpretive Summary: Viroids are the smallest known agents of infectious disease ' small, circular RNA molecules that lack the coat protein characteristic of most conventional viruses yet are able to multiply and cause disease in susceptible host plants. At the molecular level, viroid multiplication requires these molecules to switch between several very different conformations. Comparison of the sequences of Potato spindle tuber viroid and several related viroids suggests that a specific portion of their usual structure may rearrange to form a 'pseudoknot', and this manuscript describes a series of mutagenesis experiments designed to prove/disprove this hypothesis. Understanding how viroids replicate is key to ongoing efforts to render plants resistant to viroid infection. This report will be of greatest interest to researchers interested in RNA molecular biology, especially the molecular interactions between viroids and viruses and their plant hosts.

Technical Abstract: Comparative sequence analysis suggests that the left terminal domain of Potato spindle tuber viroid (PSTVd) may assume a branched tertiary structure. To search for evidence of such a structure in vivo, we mutagenized the sequences proposed to interact, inoculated tomato seedlings with mixtures of potentially infectious PSTVd RNA transcripts, and screened the resulting progeny for sequence changes consistent with the alternative base pairings. PSTVd positions 6-11 and 330-335 tolerated only limited sequence variation, and compensatory changes were observed in only one of 15 plants examined. Passage of certain variants in Rutgers tomato was accompanied by full or partial sequence reversion and an increase in virulence, suggesting that maintenance of the rod-like structure of the left terminal domain is more important for viroid fitness than the ability to assume a branched conformation containing one or more pseudoknots.