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Dynamics of asexual transmission of a mitochondrial plasmid in Cryphonectria parasitica
D Baidyaroy1, J M Glynn, H Bertrand
1Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312, USA.
Abstract:
In the chestnut blight fungus Cryphonectria parasitica, as in most fungi, little is known about the efficiency of the asexual transmission of optional mitochondrial plasmids, vertically through conidia, and horizontally through hyphal anastomoses. In this paper, we show that pCRY1, a circular mitochondrial plasmid, is transmitted vertically with 100%-efficiency through conidia. Moreover, the plasmid is transmitted horizontally through hyphal contact from donor strains to vegetatively compatible and most incompatible strains. An allelic difference between the donor and recipient strain, at only one of the five nuclear incompatibility genes that were tested strongly inhibited, but did not absolutely prevent, the transfer of pCRY1 through hyphal fusions. In contrast, allelic differences in any one or several of the other four heterokaryon-compatibility loci suppressed the transmission of the plasmid only partially or not at all. The plasmid was also transmitted among incompatible strains by protoplast fusion without the concomitant transfer of mitochondrial DNA (mtDNA). A comparison of plasmid-bearing with plasmid-free isogenic strains revealed that pCRY1 significantly diminishes the pathogenic potency of some strains of the fungus, but does not affect the virulence of others. Collectively, the observations indicate that the introduction of deleterious mitochondrial genetic elements into natural populations may be a means for managing fungal pathogens.
Insights
The mitochondrial plasmid pCRY1 transmits efficiently in chestnut blight fungus Cryphonectria parasitica via conidia and hyphal contact. This plasmid can reduce fungal pathogenicity, suggesting potential for biological control strategies.
Area of Science:
- Mycology
- Plant Pathology
- Genetics
Background:
- Mitochondrial plasmids are common in fungi but their transmission dynamics are poorly understood.
- Optional plasmids like pCRY1 in Cryphonectria parasitica play roles in fungal biology and pathogenicity.
Purpose of the Study:
- To investigate the transmission efficiency of the mitochondrial plasmid pCRY1 in Cryphonectria parasitica.
- To determine the impact of nuclear genetic background and vegetative compatibility on plasmid transmission.
- To assess the effect of pCRY1 on the pathogenicity of C. parasitica.
Main Methods:
- Assessing vertical transmission of pCRY1 through fungal conidia.
- Evaluating horizontal transmission of pCRY1 via hyphal anastomoses between compatible and incompatible strains.
- Utilizing protoplast fusion to study plasmid transfer independent of mitochondrial DNA.
- Comparing pathogenicity of isogenic plasmid-bearing and plasmid-free strains.
Main Results:
- pCRY1 exhibits 100% vertical transmission efficiency through conidia.
- Horizontal transmission occurs between compatible and most incompatible strains, with strong inhibition by allelic differences at one specific nuclear incompatibility gene.
- Protoplast fusion allows pCRY1 transmission without concomitant mtDNA transfer.
- pCRY1 reduces pathogenicity in some C. parasitica strains but not others.
Conclusions:
- Mitochondrial plasmid pCRY1 is efficiently transmitted both vertically and horizontally in Cryphonectria parasitica.
- Nuclear genetic background, particularly specific incompatibility genes, influences plasmid transmission.
- Deleterious mitochondrial genetic elements like pCRY1 may offer a strategy for managing fungal pathogens.