The small GTPase Rac and the p21-activated kinase Cla4 in Claviceps purpurea: interaction and impact on polarity, development and pathogenicity

Mol Microbiol. 2008 Apr;68(2):405-23. doi: 10.1111/j.1365-2958.2008.06159.x. Epub 2008 Feb 19.


Claviceps purpurea, the ergot fungus, is a highly specialized pathogen of grasses; its colonization of host ovarian tissue requires an extended period of strictly polarized, oriented growth towards the vascular tissue. To understand this process, we study the role of signalling factors affecting polarity and differentiation. We showed that the small GTPase Cdc42 is involved in polarity, sporulation and in planta growth in C. purpurea. Here we present evidence that the GTPase Rac has an even stronger and, in some aspects, inverse impact on growth and development: Deltarac mutants form coralline-like colonies, show hyper-branching, loss of polarity, sporulation and ability to penetrate. Functional analyses and yeast two-hybrid studies prove that the p21-activated kinase Cla4 is a major downstream partner of Rac. Phosphorylation assays of MAP kinases and expression studies of genes encoding reactive oxygen species (ROS)-scavenging and -generating enzymes indicate a function of Rac and Cla4 in fungal ROS homoeostasis which could contribute to their drastic impact on differentiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Claviceps / enzymology
  • Claviceps / genetics
  • Claviceps / growth & development*
  • Claviceps / pathogenicity*
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • Gene Deletion
  • Gene Expression Profiling
  • Genetic Complementation Test
  • Hyphae / growth & development
  • Lolium / microbiology
  • Lolium / ultrastructure
  • Microscopy, Electron, Scanning
  • Models, Biological
  • Phosphorylation
  • Protein Binding
  • Two-Hybrid System Techniques
  • p21-Activated Kinases / genetics
  • p21-Activated Kinases / metabolism*
  • rac GTP-Binding Proteins / genetics
  • rac GTP-Binding Proteins / metabolism*


  • Fungal Proteins
  • p21-Activated Kinases
  • rac GTP-Binding Proteins