Structural characteristics and possible horizontal transfer of group I introns between closely related plant pathogenic fungi.
We have characterized structural features and the distribution pattern of nuclear group I introns found in ribosomal DNA (rDNA) of closely related plant pathogenic fungi of the family Sclerotiniaceae. Sixteen introns, at two distinct positions in the small-subunit (SSU) and large-subunit (LSU) rDNA, were sequenced and analyzed among the 29 taxa included in the initial screening. Genera found to contain introns were Botrytis, Dumontinia, Encoelia, Grovesinia, Myriosclerotinia, and Sclerotinia. Secondary-structure analyses of the group I introns concluded that all belong to the common IC1 subclass. Interestingly, the SSU rDNA intron from Myriosclerotinia caricisampullacea contains an insertion-like sequence extension which may be a relic of an open reading frame. Incongruent branching patterns of intron-based and rDNA-based (internal transcribed spacer) phylogenetic trees suggest that the fungal host genomes and the group I introns do not share a common evolutionary history. A model to explain how horizontal intron transfers may have occurred among the closely related fungal taxa is proposed.
Holst-Jensen
A
A
Department of Biology, University of Oslo, Norway. arne.holst-jensen@vetinst.no
Vaage
M
M
Schumacher
T
T
Johansen
S
S
D000595:Amino Acid Sequence; D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D005658:Fungi / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D022761:Gene Transfer, Horizontal; D005800:Genes, Fungal; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D010944:Plants / Q000382:microbiology*; D012331:RNA, Fungal / Q000737:chemistry / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid
D004271:DNA, Fungal; D004275:DNA, Ribosomal; D012331:RNA, Fungal