Analysis of double-stranded RNA and virus-like particles in trichothecene-producing strains ofFusarium graminearum

Double-stranded RNAs (dsRNAs) have been found in two isolates of the plant pathogenic fungus Fusarium graminearum which produce trichothecene mycotoxins. The isolates 8.2 and 19.2 had dsRNAs in the size of about 2.0 kb and 6.0 kb, respectively, which were associated with capsid proteins and persisted within the cytoplasm of the infected host cells as encapsidated virus-like particles (VLPs). The dsRNAs contained in the VLP pellets were the same size as the dsRNA isolated in total nucleic acid preparations. In the VLP pellets the isolate 19.2 had a second dsRNA with the size of about 1.6 kb. After mycovirus purification one icosahedral particle of about 28 nm in diameter from the isolate 8.2 and two icosahedral particles of about 28 nm and 38 to 40 nm in diameter from the isolate 19.2 could be identified with electron microscopy. SDS-PAGE analysis of the VLPs from the isolate 8.2 revealed one major protein component of approximately 65 kDa, while the isolate 19.2 had two major protein bands at about 94 kDa and 105 kDa. Both isolates were studied for potential trichothecene production. Tox5 PCR showed a 658 bp fragment in each isolate. In addition, both strains were able to produce the trichothecenes deoxynivalenol (DON), the derivatives acetyl-DON (3-A-DON, 15-A-DON) and nivalenol (NIV) in vitro.