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Repeat-induced point mutation (RIP) as an alternative mechanism of evolution toward virulence in Leptosphaeria

Isabelle Fudal1, Simon Ross, Hortense Brun

  • 1INRA UMR 1290 BIOGER-CPP, F-70826 Versailles, France.

Molecular Plant-Microbe Interactions : MPMI
|July 11, 2009
PubMed

Insights

Repeat-induced point mutation (RIP) rapidly drives virulence in Leptosphaeria maculans by disabling the AvrLm6 avirulence gene. This study reveals RIP as a key evolutionary mechanism in plant pathogens.

Area of Science:

  • Plant Pathology
  • Molecular Evolution
  • Genetics

Background:

  • Leptosphaeria maculans causes significant crop losses in Brassica species.
  • Avirulence genes, such as AvrLm1, AvrLm6, and AvrLm4-7, are crucial for pathogen recognition and host resistance.
  • The Rlm6 resistance gene was rapidly overcome, necessitating an investigation into the evolution of virulence at the AvrLm6 locus.

Purpose of the Study:

  • To investigate the molecular mechanisms underlying the evolution of virulence at the AvrLm6 locus in Leptosphaeria maculans.
  • To determine the frequency and nature of genetic changes associated with AvrLm6 loss in virulent isolates.
  • To identify the role of repeat-induced point mutation (RIP) in the rapid evolution of virulence.

Main Methods:

  • Whole-genome sequencing of a virulent Leptosphaeria maculans isolate to analyze the AvrLm6 locus.
  • Screening of 70 virulent isolates for the presence or absence of the AvrLm6 gene.
  • Sequencing of virulent AvrLm6 alleles from 24 isolates to identify point mutations and RIP events.

Main Results:

  • A 235 kb region analysis revealed the deletion of AvrLm6 and the presence of retrotransposon mosaics in a virulent isolate.
  • AvrLm6 was absent in 66% of the 70 virulent isolates examined, indicating multiple deletion events.
  • Repeat-induced point mutation (RIP) was identified as the most frequent mutation type, causing significant base modifications and stop codon generation, leading to virulence.

Conclusions:

  • Repeat-induced point mutation (RIP) is a highly efficient mechanism driving virulence evolution in Leptosphaeria maculans by inactivating avirulence genes like AvrLm6.
  • Multiple, independent RIP events can occur within a single field population annually, contributing to the rapid emergence of pathogen virulence.
  • Understanding these evolutionary dynamics is critical for developing durable disease resistance strategies in crops.

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