July 7, 2019  |  

Genome of an arbuscular mycorrhizal fungus provides insight into the oldest plant symbiosis.

Authors: Tisserant, Emilie and Malbreil, Mathilde and Kuo, Alan and Kohler, Annegret and Symeonidi, Aikaterini and Balestrini, Raffaella and Charron, Philippe and Duensing, Nina and Frei dit Frey, Nicolas and Gianinazzi-Pearson, Vivienne and Gilbert, Luz B and Handa, Yoshihiro and Herr, Joshua R and Hijri, Mohamed and Koul, Raman and Kawaguchi, Masayoshi and Krajinski, Franziska and Lammers, Peter J and Masclaux, Frederic G and Murat, Claude and Morin, Emmanuelle and Ndikumana, Steve and Pagni, Marco and Petitpierre, Denis and Requena, Natalia and Rosikiewicz, Pawel and Riley, Rohan and Saito, Katsuharu and San Clemente, Hélène and Shapiro, Harris and van Tuinen, Diederik and Bécard, Guillaume and Bonfante, Paola and Paszkowski, Uta and Shachar-Hill, Yair Y and Tuskan, Gerald A and Young, J Peter W and Young, Peter W and Sanders, Ian R and Henrissat, Bernard and Rensing, Stefan A and Grigoriev, Igor V and Corradi, Nicolas and Roux, Christophe and Martin, Francis

The mutualistic symbiosis involving Glomeromycota, a distinctive phylum of early diverging Fungi, is widely hypothesized to have promoted the evolution of land plants during the middle Paleozoic. These arbuscular mycorrhizal fungi (AMF) perform vital functions in the phosphorus cycle that are fundamental to sustainable crop plant productivity. The unusual biological features of AMF have long fascinated evolutionary biologists. The coenocytic hyphae host a community of hundreds of nuclei and reproduce clonally through large multinucleated spores. It has been suggested that the AMF maintain a stable assemblage of several different genomes during the life cycle, but this genomic organization has been questioned. Here we introduce the 153-Mb haploid genome of Rhizophagus irregularis and its repertoire of 28,232 genes. The observed low level of genome polymorphism (0.43 SNP per kb) is not consistent with the occurrence of multiple, highly diverged genomes. The expansion of mating-related genes suggests the existence of cryptic sex-related processes. A comparison of gene categories confirms that R. irregularis is close to the Mucoromycotina. The AMF obligate biotrophy is not explained by genome erosion or any related loss of metabolic complexity in central metabolism, but is marked by a lack of genes encoding plant cell wall-degrading enzymes and of genes involved in toxin and thiamine synthesis. A battery of mycorrhiza-induced secreted proteins is expressed in symbiotic tissues. The present comprehensive repertoire of R. irregularis genes provides a basis for future research on symbiosis-related mechanisms in Glomeromycota.

Journal: Proceedings of the National Academy of Sciences of the United States of America
DOI: 10.1073/pnas.1313452110
Year: 2013

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