Elucidating the Evolution of Mutualistic Plant Fungi
The large variety of fungi that exist in forest soils play diverse and important roles when in association with plant roots. One such type, the ectomycorrhizal (ECM) fungi, is a beneficial mutualist. ECM fungi obtain carbon compounds from the host plant, and in doing so provide critical ecological services such as decomposing lignocellulose and promoting plant growth. To unravel the mechanisms of nutrient cycling in forests, a better understanding of ECM fungi is needed. As part of a consortium investigating mycorrhizal fungal genomics, scientists at Oak Ridge National Laboratory, funded through the Department of Energy’s (DOE) Plant-Microbe Interfaces Science Focus Area, and DOE’s Joint Genome Institute performed phylogenomic and comparative genomic analyses of newly sequenced fungal genomes, including 13 ECM fungi, to elucidate the genetic bases of mycorrhizal lifestyle evolution. They found that although the ECM fungi have a reduced complement of genes encoding plant cell-wall degrading enzymes, those enzymes that were retained made up a distinct suite, indicating that they possess diverse capabilities to decompose lignocellulose. They also found that the symbiosis that develops between ECM fungi and the host plant and contributes to plant development and immunity requires lineage-specific fungal genes, including genes that code for mycorrhiza-induced small secreted proteins. The researchers conclude that convergent evolution of the mycorrhizal habit in fungi occurred via the repeated evolution of a “symbiosis toolkit”, with reduced numbers of plant cell-wall degrading enzymes and lineage-specific suites of mycorrhiza-induced genes. Studies designed to predict the response of ECM and other mycorrhizal fungi to fluctuations in the environment will benefit from these genomic resources.
Kohler, A., A. Kuo, L. G. Nagy, E. Morin, K. W. Barry, F. Buscot, B. Canbäck, C. Choi, N. Cichocki, A. Clum, J. Colpaert, A. Copeland, M. D. Costa, J. Doré, D. Floudas, G. Gay, M. Girlanda, B. Henrissat, S. Herrmann, J. Hess, N. Högberg, T. Johansson, H.-R. Khouja, K. LaButti, U. Lahrmann, A. Levasseur, E. A. Lindquist, A. Lipzen, R. Marmeisse, E. Martino, C. Murat, C. Y. Ngan, U. Nehls, J. M. Plett, A. Pringle, R. A. Ohm, S. Perotto, M. Peter, R. Riley, F. Rineau, J. Ruytinx, A. Salamov, F. Shah, H. Sun, M. Tarkka, A. Tritt, C. Veneault-Fourrey, A. Zuccaro, Mycorrhizal Genomics Initiative Consortium, A. Tunlid, I. V. Grigoriev, D. S. Hibbett, and F. Martin. 2015. “Convergent Losses of Decay Mechanisms and Rapid Turnover of Symbiosis Genes in Mycorrhizal Mutualists,” Nature Genetics 47, 410-15, DOI:, DOI: 10.1038/ng.3223.