Genetic Organization of the dsRNA Element Associated with Strain NB58 of the Chestnut Blight Fungus and Preliminary Examination of a dsRNA-Free Mutant

Strain NB58 of the chestnut blight fungus, Cryphonectria parasitica, is a highly debilitated strain that contains one major double-stranded (ds) RNA molecule. We have completed the primary characterization of this dsRNA, including its cDNA cloning and nucleotide sequence analysis. NB58 dsRNA has a size of 12,507 base pairs, excluding the poly (A) tail at the 3' end of the plus strand. The organization of the NB58 genome is similar to that of the largest EP713 dsRNA. On the poly (A)-containing strand, a long non-translated region preceded two open reading frames, designated ORF A and ORF B. The two open reading frames are connected by a UAAUG pentanucleotide that terminates ORF A and initiates ORF B. NB58 and EP 713 share approximately 60 percent nucleotide sequence identity. In contrast to EP713, the NB58 ORF A product does not appear to undergo autoproteolysis. In a separate but related study, a stable, dsRNAfree sector of NB58, designated NB58F, was isolated and partially characterized. NB58F was intermediate between NB58 and its isogenic, dsRNA-free parent strain, NB58-19, in terms of virulence and cultural characteristics. In repeated attempts, we have not been able to introduce dsRNA into strain NB58F.

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Author(s): Bradley I. Hillman, James J. Polashock, Matthew P. Brown, Barbara T. Halpern

Publication: American Chestnut Proceedings - 1992