The genome of the fern pathogen Mixia osmundae reveals hints about its cryptic biology
M. TOOME (1), R. W. Riley (2), T. Y. James (3), K. L. Lazarus (3), B. Henrissat (4), O. A. Robin (2), I. V. Grigoriev (2), J. W. Spatafora (5), M. C. Aime (1). (1) Purdue University, West Lafayette, IN, U.S.A.; (2) U.S. Department of Energy Joint Genome Institute, Walnut Creek, CA, U.S.A.; (3) University of Michigan, Ann Harbor, MI, U.S.A.; (4) CNRS and Aix-Marseille University, Marseille, France; (5) Oregon Sta
<i>Mixia osmundae</i> (Nishida) C.L. Kramer (Pucciniomycotina, Mixiomycetes) is a rarely encountered basidiomycete that infects ferns belonging to the genus <i>Osmunda</i> L. (Pteridophyta, Polypodiopsida). The fungus causes small chlorotic lesions on fern leaves that become covered in a white powdery layer. This layer is formed by spores that are exogenously produced on the surface of a large sac-like sporogenous cell, a characteristic structure unique to <i>M. osmundae</i>. As <i>M. osmundae</i> is not commonly found, many aspects of the biology of this fungus are unknown, including whether the spores are produced via mitosis or meiosis. We conducted whole genome analyses of <i>M. osmundae</i> to answer these and other questions. We have determined that the spores produced on fern leaves are haploid and likely produced asexually. We also detected that although <i>M. osmundae</i> possesses the genetic pathways for breaking down various plant cell wall components, it is not able to digest and produce glucose or xylose from them. These and other genomic data hint that the pathogen is a biotroph, although not an obligate biotroph since it also has a budding state that can be maintained in culture. To date, <i>M. osmundae</i> has been collected only from Asia and the eastern United States; however, our searches through sequence databases indicate that the genus might also be present in Europe and that this monotypic class may have other undiscovered members.
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