Movement of a small mitochondrial double-stranded RNA element of Cryphonectria parasitica: ascospore inheritance and implications for mitochondrial recombination

Abstract

Movement via somatic fusion and inheritance of a small mitochondrial double-stranded (ds) RNA element was examined in Cryphonectria parasitica. The 2.7-kb dsRNA from the C. parasitica strain NB631 encodes a putative RNA-dependent RNA polymerase when the mitochondrial code (UGA = Trp) is invoked. All progeny from asexual spores (conidia) of strain NB631 examined for dsRNA contained the 2.7-kb element. Unlike other C. parasitica dsRNAs, which are cytoplasmic, the dsRNA in strain NB631 was transmitted through the sexual cycle (ascospores) if the strain containing the element acted as the female in crosses. Movement of the 2.7-kb dsRNA was also observed through hyphal anastomosis. Transfer by anastomosis was accompanied by mitochondrial movement and recombination of the mitochondrial genome as determined by RFLP analysis. In control pairings between isolates lacking dsRNA, mitochondrial movement and recombination were also observed. Transfer by anastomosis allowed the generation of infected and uninfected isogenic lines, and permitted us to evaluate the effects of the dsRNA element on virulence of the host. Bark virulence assays on American chestnut suggest that NB631 dsRNA decreases the virulence of C. parasitica, but not to the level associated with members of the Hypoviridae.

Comparative Analysis of Alterations in Host Phenotype and Transcript Accumulation following Hypovirus and Mycoreovirus Infections of the Chestnut Blight Fungus Cryphonectria parasitica

“…In the current study, we confirmed the finding of female fertility in strain MyRV2-CpC18/EP155 as well as in MyRV1-Cp9B21/EP155 and determined that virus was transmitted maternally in both strains. Interestingly, the efficiency of virus transmission vertically through ascospores, approximately 60%, is about the same as that for the mitochondrial virus (28), although presumably the mechanisms of transmission are quite different.…”

Effect of putative mitoviruses on in vitro growth of Gremmeniella abietina isolates under different laboratory conditions

“…They lack true virions, and have a (+) ssRNA genome of approximately 2.5 kb (Boland, 2004). Mitoviruses have been recorded in several phytopathogenic fungi such as Cryphonectria parasitica (Polashock and Hillman, 1994;Polashock et al, 1997), Ophiostoma novo-ulmi (Brasier, 1983;Rogers et al, 1987), Sclerotina homoeocarpa (Deng et al, 2003;Deng and Boland, 2004), Helicobasidium mompa (Osaki et al, 2005), Chalara elegans (Park et al, 2006) and Botrytis cinerea (Castro et al, 2003;Wu et al, 2007). In most cases, the presence of mitoviruses is associated with reduction of fungal pathogenicity (Ghabrial and Suzuki, 2009;Wu et al, 2010).…”

Mitochondrial Genome Recombination in the Zone of Contact Between Two Hybridizing Conifers

“…Most of this controversy is related to the increasing amount of evidence suggesting recombination as the possible source of some of the mitochondrial types (mitotypes) observed in different organisms. Although polemical, the signature of recombination has been reported in the mitochondrial genome of a variety of species, including humans (e.g., Awadalla et al 1999), ruminants (Slate and Phua 2003;Tsaousis et al 2005), fish (e.g., Buroker et al 1990;Hoarau et al 2002;Tsaousis et al 2005), mollusks (e.g., Ladoukakis and Zouros 2001), nematodes (Lunt and Hyman 1997), insects (e.g., Dowton et al 2003;Tsaousis et al 2005), yeasts (e.g., Toth et al 1998;Anderson et al 2001), and filamentous fungi (e.g., Polashock et al 1997;Saville et al 1998), among others. In plants, the only direct evidence for intermolecular mtDNA recombination has been reported in the gynodioecious plant Silene acaulis (Städler and Delph 2002).…”