title: A double-stranded RNA element from a hypovirulent strain of Rhizoctonia solani occurs in DNA form and is genetically related to the pentafunctional AROM protein of the shikimate pathway.
abstract: M2 is a double-stranded RNA (dsRNA) element occurring in the hypovirulent isolate Rhs 1A1 of the plant pathogenic basidiomycete Rhizoctonia solani. Rhs 1A1 originated as a sector of the virulent field isolate Rhs 1AP, which contains no detectable amount of the M2 dsRNA. The complete sequence (3,570 bp) of the M2 dsRNA has been determined. A 6.9-kbp segment of total DNA from either Rhs 1A1 or Rhs 1AP hybridizes with an M2-specific cDNA probe. The sequences of M2 dsRNA and of PCR products generated from Rhs 1A1 total DNA were found to be identical. Thus this report describes a fungal host containing full-length DNA copies of a dsRNA element. A major portion of the M2 dsRNA is located in the cytoplasm, whereas a smaller amount is found in mitochondria. Based on either the universal or the mitochondrial genetic code of filamentous fungi, one strand of M2 encodes a putative protein of 754 amino acids. The resulting polypeptide has all four motifs of a dsRNA viral RNA-dependent RNA polymerase (RDRP) and is phylogenetically related to the RDRP of a mitochondrial dsRNA associated with hypovirulence in strain NB631 of Cryphonectria parasitica, incitant of chestnut blight. This polypeptide also has significant sequence similarity with two domains of a pentafunctional polypeptide, which catalyzes the five central steps of the shikimate pathway in yeast and filamentous fungi.
authors.affiliation: Department of Biological Sciences, University of Maine, Orono, ME 04469-5722, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Lakshman
authors.forename: J
authors.initials: J
authors.lastname: Jian
authors.forename: S M
authors.initials: SM
authors.lastname: Tavantzis
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012331:RNA, Fungal / Q000235:genetics*; D012232:Rhizoctonia / Q000235:genetics* / Q000472:pathogenicity; D017421:Sequence Analysis; D014774:Virulence
chemical_list: D018076:DNA, Complementary; D004271:DNA, Fungal; D005656:Fungal Proteins; D012331:RNA, Fungal