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Movement of a small mitochondrial double-stranded RNA element of Cryphonectria parasitica: ascospore inheritance and
J J Polashock1, P J Bedker, B I Hillman
1Department of Plant Pathology, Rutgers University, New Brunswick, NJ 08903, USA.
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.
Insights
This study investigated a unique mitochondrial double-stranded (ds) RNA element in Cryphonectria parasitica. The dsRNA element was found to decrease fungal virulence and transmit through sexual and asexual reproduction.
Area of Science:
- Mycology
- Molecular Biology
- Plant Pathology
Background:
- Cryphonectria parasitica is a significant pathogen of American chestnut.
- Mitochondrial double-stranded (ds) RNA elements can influence fungal phenotypes, including virulence.
- Previous studies focused on cytoplasmic dsRNAs, leaving sexual transmission unexamined.
Purpose of the Study:
- To investigate the transmission and effects of a specific 2.7-kb mitochondrial dsRNA element in Cryphonectria parasitica.
- To determine the inheritance patterns of this dsRNA through asexual and sexual reproduction.
- To assess the impact of the dsRNA element on the virulence of C. parasitica.
Main Methods:
- Somatic fusion and hyphal anastomosis experiments were conducted.
- Transmission through asexual spores (conidia) and sexual spores (ascospores) was analyzed.
- Restriction fragment length polymorphism (RFLP) analysis was used to study mitochondrial genome recombination.
- Bark virulence assays on American chestnut were performed.
Main Results:
- The 2.7-kb dsRNA element was consistently found in asexual progeny of strain NB631.
- Unlike other dsRNAs, this element was transmitted through the sexual cycle when NB631 acted as the female parent.
- Hyphal anastomosis facilitated dsRNA transfer, accompanied by mitochondrial movement and recombination.
- Virulence assays indicated that the NB631 dsRNA decreased C. parasitica virulence, though not as severely as Hypoviridae-associated dsRNAs.
Conclusions:
- The 2.7-kb dsRNA element in C. parasitica exhibits unique transmission characteristics, including sexual cycle inheritance.
- This dsRNA element has a hypovirulence-associated effect, reducing fungal pathogenicity.
- The findings contribute to understanding dsRNA dynamics and their impact on fungal-plant interactions.