Genomics of arbuscular mycorrhizal fungi: Out of the shadows
Résumé
Arbuscular mycorrhizal (AM) symbiosis is the most widespread mutualistic association. It concerns 80% of land plants and involves fungi belonging to the phylum Glomeromycota. Benefits to the host plants due to this symbiosis range from nutrient supply to protection against pathogens. AM fungi are important components of the soil microbiome and are of great interest for managing sustainable agriculture, provided that their life cycle is better understood. Recently, major advances in the genomics of the model AM fungus Rhizophagus irregularis DAOM197198 have been published, offering new tools to investigate the biology of this symbiosis. In this chapter, we provide an overview of the efforts that were necessary to reach these results, from the discovery of these fungi and the description of their mutualistic incidence to their in vitro cultivation and on to genomics. The genome of DAOM197198 is estimated at ca. 150 Mb. It is haploid and less polymorphic than expected. Although it is an obligate biotrophic fungus, very little gene loss was observed. We put the Rhizophagus gene repertoire in perspective with previous investigations performed on the physiology of AM fungi: germination, early signalling with host plants, plant invasion, metabolism (phosphorous, carbon and nitrogen) and sexuality. Clearly, the publication of the genome of R. irregularis DAOM197198 is a turning point in the study of AM fungi, and large areas of their biology that still remain to be elucidated will now become accessible for investigation.