1999 Workshop Abstracts | Virus Evolution Home Page | Plant Biology Home Page

Genomes of citrus tristeza virus isolates from distal environments, origins and time are essentially identical

Maria R. Albiach-Marti, Munir Mawassi, Siddarame Gowda, Tatineni Satyanarayana and William O. Dawson
University of Florida, Department of Plant Pathology,
Citrus Research and Education center, Lake Alfred, FL 33850

The complete sequence of the major component of three Citrus tristeza closterovirus (CTV) severe isolates (T36 from Florida, VT from Israel and SY568 from California) and one CTV mild isolate (T385 from Spain) have been determined. Nucleotide and amino acid sequence comparisons between these genomic sequences revealed a large potential for variation (up to 60% of nucleotide differences plus multiple insertions and deletions in some genome regions) of this positive single-stranded 19.3 kb RNA virus. Information as to whether or not this variation results from relatively rapid viral evolution is of great relevance for the design of disease management strategies, including genetically engineered mild-strain cross protection and RNA-mediated transgenic resistance. We determined the complete sequence of an independent CTV isolate with a mild phenotype T30, which has been endemic in Florida probably for a century, to enable nucleotide and amino acid sequence comparisons with other isolates. Surprisingly, our results showed that the CTV isolates T30 and T385, which have been maintained in different environments and separated for at least 23 years, but probably much longer, were nearly identical (142 nucleotide differences per genome, 0.7% nucleotide variability, only 6% of these nucleotide changes resulted in dissimilar amino acids). Additionally, sequences of CTV genome regions known to have high nucleotide variability were sampled from other independent CTV mild isolates, separated in time, from different parts of the world. Isolates B252 (from Taiwan), B272 (from Colombia), and B354 (from California) were also almost identical in sequence to T30 (from 0.4 to 0.8% nucleotide variability). Moreover, the nucleotide variability of these five isolates are near the range of the T30 quasispecies sequence variation (~ 0.5% nucleotide variability), suggesting that T30, T385 and probably B252, B272 and B354, are essentially identical. Considering that nucleotide similarities of other CTV isolates (T36, VT and SY568) are more distant than expected for strains of the same virus, conservation of the sequences of T30, T385, B252, B272 and B354 suggests high genetic stability of this genotype. Significant changes in some CTV genotypes might occur over long periods of time.

Abstracts from the Virus Evolution Workshop
Ardmore, OK
October 21 - 24th, 1999

Virus Evolution Workshop - Main Page
Poster Presentations

To contact the organizers:
e-mail: mroossinck@noble.org

Dr. Marilyn Roossinck
Plant Biology Division
The Noble Foundation
P.O. Box 2180
Ardmore, OK 73402

phone: 580 224-6630