Mitochondrial plasmid-like elements in some hypovirulent strains of Cryphonectria parasitica

In the chestnut blight fungus Cryphonectria parasitica, cytoplasmically transmissible hypovirulence phenotypes are elicited by debilitating mitochondria! DNA (mtDNA) mutations. In virus-free hypovirulent strains of C. parasitica from nature, the presence of a mitochondrial DNA element, named InC9, has been reported to cause similar disease syndromes. We have detected an additional mitochondrial element, termed pIME-C9 (plasmid-like mitochondrial element C9) in some of the strains rendered hypovirulent by InC9. This element is a 1.4-kb DNA that exists in the mitochondria as monomeric and multimeric circular forms. Only a short 127-bp sequence of the pIME-C9 DNA is derived from a region of the C. parasitica mtDNA that contains a reverse transcriptase-like open reading frame. The accumulation of the pIME-C9 DNA in the mitochondria appears to adversely affect the growth of the fungus on synthetic medium. However, the presence pIME-C9 in different strains did not correlate with the manifestation of the hypovirulence phenotype, indicating that it is not the primary reason for the prevalence of attenuated C. parasitica strains in the Kellogg Forest in Michigan. (C) 2011 Elsevier Inc. All rights reserved.