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Keywords:

  • ectomycorrhizal symbiosis;
  • Hebeloma cylindrosporum;
  • mycorrhiza differentiation;
  • nitrogen assimilation;
  • Pinus sp.;
  • population dynamics

Contents

  • Summary 481

  • I. 
    Introduction 482
  • II. 
    Taxonomy, distribution, autecology, and host range of H. cylindrosporum 482
  • III. 
    The Hebeloma cylindrosporum toolbox 483
  • IV. 
    Mycorrhiza differentiation 486
  • V. 
    Nutritional interactions 488
  • VI. 
    Genetic diversity and dynamics of H. cylindrosporum populations in P. pinaster forest ecosystems  491
  • VII. 
    Future directions 494
  • Acknowledgements 494

  • References 494

Summary

The basidiomycete Hebeloma cylindrosporum has been extensively studied with respect to mycorrhiza differentiation and metabolism and also to population dynamics. Its life cycle can be reproduced in vitro and it can be genetically transformed. Combined biochemical, cytological, genetical and molecular approaches led to the characterisation of mutant strains affected in mycorrhiza formation. These studies demonstrated the role of fungal auxin as a signal molecule in mycorrhiza formation and should allow the characterisation of essential fungal genes necessary to achieve a compatible symbiotic interaction. Random sequencing of cDNAs has identified numerous key functional genes which allowed dissection of essential nitrogen assimilation pathways. H. cylindrosporum also proved to be a remarkable model species to uncover the dynamics of natural populations of ectomycorrhizal fungi and the way in which they respond and adapt to anthropogenic disturbance of the forest ecosystem. Although studies on mycorrhiza differentiation and functioning and those on the population dynamics of H. cylindrosporum have been carried out independently, they are likely to converge in a renewed molecular ecophysiology which will envisage how ectomycorrhizal symbiosis functions under varying field conditions.