Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2007
Publication Date: 12/1/2007
Citation: Machida, S., Yamahata, N., Watanuki, H., Owens, R.A., Sano, T. 2007. Successive accumulation of two size classes of viroid-specific small RNA in potato spindle tuber viroid-infected tomato plants. Journal of General Virology. 88:3452-3457. 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. 'RNA silencing' is a diverse group of RNA-based processes used by plant and animal cells to i) regulate expression of their genomes during normal growth and development and ii) combat invasion by foreign nucleic acids. RNA silencing has been shown to play an important role in symptom development during viroid infection, but just how and where the small viroid-related RNAs are generated during the infection process is not known. This report provides evidence that at least two distinct cellular pathways are involved. The information contained will be used by researchers seeking to devise novel strategies to block the molecular interactions between viroids or viruses and their plant hosts, thereby preventing disease development and reducing crop losses.
Technical Abstract: Like many plant RNA viruses, infection by potato spindle tuber viroid (PSTVd) is known to lead to RNA silencing and a marked reduction in visible disease. To examine the relationship between RNA silencing and this recovery phenomenon in greater detail, we have carried out time-course analyses of viroid-specific small RNA accumulation using several viroid-host combinations. These analyses revealed the presence of two size classes of viroid-specific small RNAs in infected plants, and sequence analysis subsequently demonstrated the presence of a previously undescribed cluster of small RNAs derived primarily from (-)strand PSTVd RNA. Although the clustering patterns were similar, the size distribution of PSTVd small RNAs isolated from symptomatic leaf tissue became more heterogeneous with time. The process by which viroid-specific small RNAs are generated appears to be more complicated than previously believed, possibly involving multiple Dicer-like activities, viroid RNA substrates, and subcellular compartments.