Ustilaginomycotina is a diverse group of non-mushroom forming fungi in the Basidiomycota. The subphylum primarily contains species known as smut fungi, which are phytopathogens that cause disease on various plants, including many agricultural crops, such as maize (caused by Ustilago maydis), wheat (caused by Tilletia tritici and T. laevis) and sugarcane (caused by Sporisorium scitamineum).
The smut fungi are facultative biotrophic pathogens that are usually dimorphic with complex life cycles. During the haploid stage (n), they appear as saprobic yeasts, infrequently detected in nature. When two sexually-compatible yeast cells mate, the pathogenic dikaryotic (n+n) hyphal stage is initiated, triggering host infection. After infection the fungus produces dusty masses of teliospores (n+n) as dispersal agents. Under favorable conditions, the teliospores will germinate and give rise to a basidium, where nuclear fusion and meiosis occur to produce basidiospores (n). Basidiospores germinate as saprobic yeasts and initiate the next cycle. Ustilago maydis, in particular, has been used as a model genetics organism.
Molecular phylogenetic studies have demonstrated that Ustilaginomycotina contains many organisms that don't display the classic "smut" life cycle and morphology, including strictly saprobic yeasts and anamorphic animal pathogens, such as lipophilic Malassezia spp., which can cause dandruff. To date, Ustilaginomycotina comprises about 1,700 described species from 115 genera, 15 orders and four classes. Despite this diversity, little is known about the evolutionary relationships between the major clades, or the life histories of many of the species within.
Through collaboration with the Joint Genome Institute (JGI) under the 1000 Fungal Genome Project, we are establishing an ordinal-level evolutionary tree of Ustilaginomycotina using a genomic-scale phylogenetic approach. These genomes will also be utilized to understand mechanisms of fungal dimorphism in this group of fungi. The study includes several aspects of physiology, genomics, transcriptomics and molecular genetics. We also focus on systematics studies which seek to discover and describe new species, especially from tropical environments.
Generalized life cycle of a smut fungus
Testicularia cyperi causing galls on a beak-rush (Rhynchospora inundata)
Culture morphologies of several anamorphic species in Ustilaginomycotina:
(left) Ceraceosorus sp., (middle) Acaromyces ingoldii and (right) Tilletiopsis washingtonensis
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Kijpornyongpan T, Mondo SJ, Barry K, Sandor L, Lee J, Lipzen A, Pangilinan J, LaButti K, Hainaut M, Henrissat B, Grigoriev IV, Spatafora JW, Aime MC. 2018. Broad genomic sampling reveals a smut pathogenic ancestry of the fungal clade Ustilaginomycotina. Molecular Biology and Evolution 35: 1840–1854. doi: 10.1093/molbev/msy072
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Toome M, Kuo A, Henrissat B, Lipzen A, Tritt A, Yoshinaga Y, Zane M, Barry K, Grigoriev IV, Spatafora JW, Aime MC. 2014. Draft genome sequence of a rare smut relative, Tilletiaria anomala UBC 951. Genome Announcements 2:e00539-14.