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United States Department of Agriculture

Agricultural Research Service

Title: Evidence for Repeat-Induced Point Mutation (Rip) among Sequences of a Putative Transposable Element from the Wheat Pathogen Mycosphaerella Graminicola

item Goodwin, Stephen
item Cavaletto, Jessica

Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 20, 2003
Publication Date: March 19, 2003
Citation: Goodwin, S.B., Tian, Y., Cavaletto, J.R. 2003. Evidence for repeat-induced point mutation (rip) among sequences of a putative transposable element from the wheat pathogen mycosphaerella graminicola (abstract). Fungal Genetics Newsletter. 50(S):153.

Technical Abstract: Repeat-induced point mutation (RIP) is a potential mechanism for inactivating transposons in fungi through introduction of C to T transitions into coding regions. This phenomenon has been analyzed thoroughly in Neurospora, but is less well studied in other fungi. A DNA fingerprint probe from the septoria tritici leaf blotch pathogen of wheat, Mycosphaerella graminicola, was shown previously to contain part of an active transposable element. Transposition of this element appeared to be stimulated by meiosis, but also occurred at a fairly high frequency in one isolate during asexual reproduction. To test for possible RIP in M. graminicola, five copies of the reverse-transcriptase gene from the putative transposable element were cloned and sequenced. A high frequency of G:C to A:T transitions characteristic of RIP was found among the sequences of the five clones. These mutations occurred not only in the reading frame for the reverse-transcriptase gene but also in the presumably non-coding regions of the transposon. All copies except one contained one or more stop codons within the region coding for the reverse transcriptase. Most of these stop-codon mutations were caused by G:C to A:T transitions, as expected if RIP is the causal mechanism. The copy of the transposon without stop codons presumably may be active. By comparison, analysis of the single-copy Sln1 gene from M. graminicola showed no evidence of RIP. This may provide the first evidence for RIP in a Loculoascomycete and indicates that this phenomenon may be important for inactivating transposons in many fungi in the genus Mycosphaerella and possibly the order Dothideales.

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