Ericoid mycorrhizal fungi and their genomes: another side to the mycorrhizal symbiosis?

Contents Summary 1141 I. Introduction 1141 II. The ericoid mycorrhizal lifestyle 1141 III. Lessons from the mycorrhizal fungal genomes 1142 IV. ERM fungi: a discordant voice in the mycorrhizal choir 1143 V. An endophytic niche for ERM fungi 1144 VI. Specialised vs unspecialised mycorrhizal fungi? 1145 VII. Conclusions and perspectives 1145 Acknowledgements 1146 References 1146 SUMMARY: The genome of an organism bears the signature of its lifestyle, and organisms with similar life strategies are expected to share common genomic traits. Indeed, ectomycorrhizal and arbuscular mycorrhizal fungi share some genomic traits, such as the expansion of gene families encoding taxon-specific small secreted proteins, which are candidate effectors in the symbiosis, and a very small repertoire of plant cell wall-degrading enzymes. A large gene family coding for candidate effectors was also revealed in ascomycetous ericoid mycorrhizal (ERM) fungi, but these fungal genomes are characterised by a very high number of genes encoding degradative enzymes, mainly acting on plant cell wall components. We suggest that the genomic signature of ERM fungi mirrors a versatile life strategy, which allows them to occupy several ecological niches.