Significance of dsRNA Genetic Elements in Plant Pathogenic Fungi

Abstract

INTRODUCTIONPhenotypic variability involving morphology, synthesis of secondary metabo lites, or virulence is not uncommon in filamentous fungi. Efforts to explain this phenomenon have stimulated interest in extrachromal genetic elements such as mycoviruses, plasmids, or transposons as modulators of fungal gene expression. DNA plasmids are not prevalent in filamentous fungi, and the incidence of transposable elements has only recently been reported (62). In contrast, mycoviruses and related double-stranded (ds) RNA genetic elements are found associated with fungi at a very high frequency. Consequently, the . contribution of these genetic elements to phenotypic variability has come under increased scrutiny.The first fungal viruses were isolated from mushrooms in 1962 (57), followed six years later by the discovery of viruses in Penicilliumfuniculosum

Effects of double-stranded RNA on virulence of Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) against the silverleaf whitefly, Bemisia tabaci strain B (Homoptera: Aleyrodidae)

“…So, the relationship of these genetic elements to virulence variability has mostly been inferred from correlative evidence, supported in some cases by curing and transmission experiments (Nuss and Koltin, 1990). In attempts to eliminate dsRNA from various fungal species, several treatments have been used, e.g., chlorate selection of nit mutants, incubation at high temperature, hot water exposure, antibiotics, acridine dye, single conidium subculture, hyphal tip transfer, UV-irradiation, and cycloheximide treatment (Pusey and Wilson, 1982;Fulbright, 1984;Hunst et al, 1986;Kousik et al, 1994;Elias and Cotty, 1996).…”

Presence of Double-Stranded RNAs in Human and Calf Isolates of Cryptosporidium parvum

“…The importance of these molecules for the parasite and its presence in human isolates with different genotypes are as yet unknown. However, because dsRNAs are common in many parasitic protozoa (Patterson, 1990;Wang and Wang, 1991), and some are known to modulate virulence of pathogenic fungi (Nuss and Koltin, 1990), we have continued to investigate the biology and occurrence of these dsRNAs in both human and animal isolates of C. parvum.…”

Essential and Dispensable Virus-Encoded Replication Elements Revealed by Efforts To Develop Hypoviruses as Gene Expression Vectors

“…Substantial alterations were tolerated in the pentanucleotide UAAUG that contains the ORF A termination codon and the overlapping putative initiation codon of the second of the two hypovirus ORFs, ORF B. Replication competence was maintained following either a frameshift mutation that caused a two-codon extension of ORF A or a modification that produced a single-ORF genomic organization. These results are discussed in terms of determinants of hypovirus replication, the potential utility of hypoviruses as gene expression vectors, and possible mechanisms by which hypoviruses recognize and delete foreign sequences.Fungi representing all major taxons have been reported to harbor viruses and related virus-like double-stranded (ds) RNA genetic elements (1,17,29). Similar to viruses of animals and plants, mycoviruses have potential utility for elucidating host functions and manipulating host phenotype (see reference 41).…”