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Title: CELL-TO-CELL MOVEMENT OF POTATO SPINDLE TUBER VIROID

Author
item DING, BIAO - DEPT OF PLANT PATH, OK
item KWON, MYOUNG-OK - DEPT OF PLANT PATH, OK
item Hammond, Rosemarie
item Owens, Robert

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/1997
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 yet are able to replicate independently and cause disease in their plant hosts. Cell-to-cell movement is an important component of the infection process, but virtually nothing is known about the pathway(s) and mechanisms involved. We have monitored the movement of potato spindle tuber viroid (PSTVd) RNA labeled with the nucleotide-specific flourescent dye TOTO-1 iodide following microinjection into single cells of mature tomato or tobacco leaves. PSTVd injected into leaf mesophyll cells was observed to move rapidly from cell to cell via plasmodesmata. In contrast, a larger nonviroid RNA was unable to move unless PSTVd-specific sequences were added to one of its termini. At the DNA level, a cDNA copy of PSTVd appears able to mediate the movement of large plasmid DNAs from cell to cell. Once the specific sequence or structural motif responsible for PSTVd movement have been identified, this information will be used to devise an effective means to block such movement (and thereby confer durable resistance to viroid infection on presently susceptible crop species). Until then, the fundamental information gathered during our studies will be of greatest interest to researchers studying host-pathogen interactions at the molecular level.

Technical Abstract: Viroids are non-translatable, autonomously-replicating circular RNAs that infect only plants. An important component of the viroid infection process is cell-to-cell movement; there is, however, virtually no information available about the pathways and mechanisms of this process. We are using potato spindle tuber viroid (PSTVd) as a model system to investigate the mechanism of viroid cell-to-cell transport. Infectious RNA transcripts were produced from PSTVd cDNA clones in vitro, labeled with the nucleotide-specific fluorescent dye TOTO-1 iodide, and used for microinjection. When injected into symplasmically isolated guard cells of mature tomato and tobacco leaves, PSTVd remained in the injected cells; in contrast, PSTVd injected into symplasmically connected mesophyll cells moved rapidly from cell to cell. A 1400 nt RNA containing only vector sequences was unable to move out of the injected mesophyll cells, but when PSTVd was fused to this transcript, the fusion RNA moved from cell to cell. At the DNA level, PSTVd cDNA also appears able to mediate cell-to-cell movement of plasmid DNA. Our data indicate that i) PSTVd moves from cell to cell via plasmodesmata and ii) this movement may be mediated by a specific sequence or structural motif.