Study on a novel dsRNA virus isolated from the white root rot fungus, Rosellinia necatrix Prillieux, W89
Date Issued
2009
Date
2009
Author(s)
Lin, Yu-Hsin
Abstract
White root rot is one of the most devastating, worldwide distributed diseases particularly in fruit trees. It is caused by a soilbrone ascomycetous fungus, osellinia necatrix Prillieux. To avoid the widespread and attack of this fungus on target plants, a control by drenching 50 to 200 L of fungicide per tree can be achieved. However, it is very labor intensive and raises environmental concerns about soil pollution. It is an attempt of developing environmentally-friendly novel management methods for controlling this phytophathogen, such as using dsRNA mycovirus to reduce the virulence of fungus.n this study, the biological and molecular properties on dsRNA isolated fromR. necatrix strain, W89 (RnV-W89) were characterized. RnV-W89 contained four segments of double-stranded (ds) RNA, namely RNA1, RNA2, RNA3 and RNA4. Complementary DNA were cloned and the terminal sequences of each segments were determined by using 3’RNA ligase mediated rapid amplification of the cDNA ends (3’RLM-RACE). The full length of each segment had the size of 4942, 4353, 4099 and 3685 bp, with the deduced amino acids of 1602, 1356, 1310 and 1061 aa, respectively. blastp homology search revealed that the ORF of RNA3 encodes RNA-dependent RNA polymerase（RdRP）that had low levels of sequence identity to the unassigned viruses, such as Amasya cherry disease-associated mycovirus and Cherry chlorotic rusty spot associated totiviral-like dsRNA 4. No significant sequence similarity was found between the deduced amino acid sequences coded by the other ORFs of RnV-W89 and the known protein sequences.s most viruses in having strictly conserved region at their 5’- and 3’- terminal sequences of genome(s) for replication, the genome of RnV-W89 showed sequence similarities between the four segments at their 5’ and 3’ untranslated region (UTR). Moreover, a second region of strong sequence similarity contained a reiteration of the unique sequence “CAA”. These (CAA)n repeats were similar to the enhancer elements presented at the 5’ UTRs of tobamoviruses. The purified viral particles had a size about 48 nm in diameter. SDS-PAGE analysis of the purified virus particles showed that the main bands had the approximate sizes of 110, 100, 75 and 63 kDa. hese results showed that four dsRNA segments of RnV-W89 were likely to be the genome segments of a novel mycovirus with a divided dsRNA genome. The present study provides the basic characteristics of dsRNA of RnV-W89. To ascertain the competence as a virocontrol agent of this virus, further studies are necessary.
Subjects
root rot disease
mycovirus
hypovirulence
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