|SANO, T - HIROSAKI UNIV JAPAN
|FELDSTEIN, P - UNIV OF MD COLLEGE PK MD
|HU, Y - UNIV OF MD COLLEGE PK
|STEGER, G - DUSSELDORF GERMANY
Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2003
Publication Date: 9/1/2003
Citation: Owens, R.A., Sano, T., Feldstein, P.A., Hu, Y., Steger, G. 2003. Identification of a novel structural interaction in columnea latent viroid. Virology.
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. The ability of Columnea latent viroid to multiply in both tomato and cucumber has led others to suggest that this viroid may have originated by recombination between two distantly related viroids. Our studies of the ability of this viroid to switch from one conformation to another in vitro suggest that the relationship between the structure of a viroid and its ability to multiply and cause disease is more complicated that previously believed. Understanding those relationships is essential if we are to reach our ultimate objective -- creation of durable resistance in crops that are currently susceptible to viroid disease. Our results will be greatest interest to researchers interested in the molecular interactions between viroids or viruses and their plant hosts.
Technical Abstract: The ability of Columnea latent viroid (CLVd) to replicate in both cucumber and tomato suggests that this pospiviroid may have originated as a result of an RNA recombination event involving Potato spindle tuber viroid (PSTVd) and Hop stunt viroid (HSVd)[Hammond et al. 1989. Nuc. Acids Res. 17, 10083-10094]. To examine the role of specific structural features in determining the host range of CLVd, we constructed a series of interspecific chimeras by replacing increasing portions of the CLVd terminal left and pathogenicity domains with the corresponding portions of PSTVd. Exchanges involving the left side of the CLVd pathogenicity domain led to lower rates of progeny accumulation in tomato, but the chimera was still able to replicate in cucumber. Exchanges involving the right side of the pathogenicity domain severely inhibited replication in tomato and appeared to abolish replication in cucumber. Several spontaneous sequence changes were observed among the progeny of the various chimera, but none involved either secondary hairpin II or other interactions known to be important for infectivity. A combination of temperature gradient gel electrophoresis and structural calculations did, however, reveal an unexpected complementarity between the upper portion of the pathogenicity domain and right terminal loop of CLVd. Like the formation of secondary hairpin III in PSTVd, this interaction may facilitate breakdown of the rod-like native structure of CLVd and formation of secondary hairpin II. It also appears to play a critical role in the infection process.