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Title: Potato spindle tuber viroid: the simplicity paradox resolved?

item Owens, Robert

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2007
Publication Date: 1/1/2008
Citation: Owens, R.A. 2007. Potato spindle tuber viroid: the simplicity paradox resolved?. Molecular Plant Pathology. 8:549-560.

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. This 'Pathogen Profile' summarizes 35 years of molecular and biological studies of the first such agent to be discovered, potato spindle tuber viroid (PSTVd). To help identify future research directions, key studies involving PSTVd replication, pathogenicity, and transport within the host plant are arranged along a timeline. Individual studies are seen to have become broader in scope and often involve several different experimental approaches. This publication will be of greatest interest to plant scientists interested in the molecular interactions between pathogens and their hosts.

Technical Abstract: Taxonomy: Potato spindle tuber viroid (PSTVd) is the type species of the genus Posipiviroid, family Pospiviroidae. An absence of hammerhead ribozymes and the presence of a 'central conserved region' distinguish PSTVd and related viroids from members of a second viroid family, the Avsunviroidae. Physical properties: Viroids are small, unencapsidated, circular, single-stranded RNA molecules which replicate autonomously when inoculated into host plants. Because viroids are non-coding RNAs, designation of the more abundant, highly infectious polarity strand as the positive strand is arbitrary. PSTVd assumes a rod-like, highly-structured conformation that is resistant to nuclease degradation in vivo. Naturally-occurring sequence variants of PSTVd range in size from 356-361 nucleotides. Hosts and symptoms: Potato and avocado are the only known natural hosts of PSTVd. Foliar symptoms in potato are often obscure, and the severity of tuber symptoms – elongation with the appearance of prominent bud scales (eyebrows) and growth cracks- depends on both temperature and length of infection. PSTVd has a broad experimental host range, especially among solanaceous species, and strains are classified as mild, intermediate, or severe based upon the symptoms observed in certain sensitive tomato cultivars. These symptoms include shortening of internodes, petioles, and mid-ribs, severe epinasty and wrinkling of the leaves, and necrosis of mid-ribs, petioles, and stems.