title: Repeat-induced point mutation (RIP) as an alternative mechanism of evolution toward virulence in Leptosphaeria maculans.
abstract: Three avirulence genes, AvrLm1, AvrLm6, and AvrLm4-7, were recently identified in Leptosphaeria maculans and found to be localized as solo genes within large noncoding, heterochromatin-like regions mainly composed of retrotransposons, truncated and degenerated by repeat-induced point mutation (RIP). The Rlm6 resistance gene has been overcome within 3 years in outdoor experiments in France and, here, we investigate the molecular basis of evolution toward virulence at the AvrLm6 locus. A region of 235 kb was sequenced in a virulent isolate and showed the deletion of AvrLm6 and three divergent mosaics of retrotransposons. AvrLm6 was found to be absent from 66% of 70 virulent isolates, with multiple events of deletion. The sequencing of virulent alleles in 24 isolates revealed a few cases of point mutations that had created stop codons in the sequence. The most frequent mutation events, however, were RIP, leading to the modification of 4 to 9% of the bases compared with the avirulent allele and generating 2 to 4 stop codons. Thus, RIP is described for the first time as an efficient mechanism leading to virulence and the multiple patterns of mutation observed suggest that multiple RIP events could occur independently in a single field population during 1 year.
authors: INRA UMR 1290 BIOGER-CPP, F-70826 Versailles, France.
authors: Isabelle
authors: I
authors: Fudal
authors: Simon
authors: S
authors: Ross
authors: Hortense
authors: H
authors: Brun
authors: Anne-Laure
authors: AL
authors: Besnard
authors: Magali
authors: M
authors: Ermel
authors: Marie-Line
authors: ML
authors: Kuhn
authors: Marie-Hélène
authors: MH
authors: Balesdent
authors: Thierry
authors: T
authors: Rouxel
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D017354:Point Mutation; D011110:Polymorphism, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014774:Virulence / Q000235:genetics
chemical_list: D005656:Fungal Proteins