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

Abstract

Contents Summary1141I.Introduction1141II.The ericoid mycorrhizal lifestyle1141III.Lessons from the mycorrhizal fungal genomes1142IV.ERM fungi: a discordant voice in the mycorrhizal choir1143V.An endophytic niche for ERM fungi1144VI.Specialised vs unspecialised mycorrhizal fungi?1145VII.Conclusions and perspectives1145Acknowledgements1146References1146 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.

The future has roots in the past: the ideas and scientists that shaped mycorrhizal research

“…We concluded that, in contrast to arbuscular mycorrhizal fungi, ericoid fungi produce cell-wall-degrading enzymes and that this capacity was probably modulated during the interaction with host and nonhost plants (Perotto et al, 1995). Indeed, genomics and transcriptomics of arbuscular mycorrhizal fungi (Tisserant et al, 2013;Salvioli et al, 2016;Chen et al, 2018) and of ericoid fungi (Kohler et al, 2015;Martino et al, 2018;Perotto et al, 2018) have demonstrated that arbuscular mycorrhizal fungi do not possess genes coding for cell-wall-degrading enzymes, in contrast to ericoid fungi, largely confirming the hypotheses advanced about 25 years before! In the absence of molecular data, ultrastructural observations have allowed researchers to look beyond the hedge: the deep reorganization of the cortical cells following the fungal colonization suggested a reprogramming of the molecular plant machinery that has been largely confirmed by RNA-sequencing studies in all the mycorrhizal symbioses (Veneault-Fourrey et al, 2014;Fiorilli et al, 2015;Peter et al, 2016;Fochi et al, 2017;Sugimura & Saito, 2017;Martino et al, 2018).…”

“…We concluded that, in contrast to arbuscular mycorrhizal fungi, ericoid fungi produce cell‐wall‐degrading enzymes and that this capacity was probably modulated during the interaction with host and nonhost plants (Perotto et al ., ). Indeed, genomics and transcriptomics of arbuscular mycorrhizal fungi (Tisserant et al ., ; Salvioli et al ., ; Chen et al ., ) and of ericoid fungi (Kohler et al ., ; Martino et al ., ; Perotto et al ., ) have demonstrated that arbuscular mycorrhizal fungi do not possess genes coding for cell‐wall‐degrading enzymes, in contrast to ericoid fungi, largely confirming the hypotheses advanced about 25 years before!…”

Diversity and community structure of ericoid mycorrhizal fungi in European bogs and heathlands across a gradient of nitrogen deposition

“…Most importantly they also form a mutualistic association with ericoid mycorrhizal fungi that is crucial to access soil nutrients otherwise unavailable for plant uptake. Ericoid mycorrhizal fungi retained more genes involved in the decomposition of lignocellulose during their evolution than ectomycorrhizal fungi (Kohler et al ., 2015; Perotto et al ., 2018), allowing them to decompose a wide range of complex and recalcitrant organic substrates. Despite their importance, little is known about the diversity of ericoid mycorrhizal fungi and the ecological factors that shape species diversity and community structure (Leopold, 2016; Kohout, 2017).…”

Cross‐scale integration of mycorrhizal function

“…Critical in this endeavor will be the use of genomic information on the recently sequenced mycorrhizal fungi (Kohler et al ., ; Martino et al ., ; Chen et al ., , pp. 1161–1171; see also Perotto et al ., , pp. 1141–1147).…”