Ceraceosorus guamensis sp. nov. culture on PDA (left) and cell morphology from yeast-malt broth (right). Bar = 2.5 mm (left) and 10 µm (right). Photos: Teeratas Kijpornyongpan.

The monotypic genus Ceraceosorus B.K. Bakshi was first described in 1976 (Cunningham et al., 1976). The type species C. bombacis was discovered on a Bombax ceiba leaf (Malvaceae) in Dehra Dun, India. The fungus was described as forming a sorus-like fructification on the lower surface of the leaf to produce discharged basidiospores. The hyphae were branched, septate and lacked clamp connections (Cunningham et al., 1976). After the first discovery, there have been no subsequent reports of Ceraceosorus in nature.
The Ceraceosorus guamensis isolate (MCA4658) selected for genome sequencing was isolated from an asymptomatic leaf phylloplane in Guam. The fungus forms light to dark brown, cerebriform, crusty colonies on a potato dextrose agar (PDA). Microscopically, the fungus forms branched, septate hyphae without clamp connections. Fusiform-shaped conidia are produced at the tip of the hypha. Based on rDNA sequence comparisons, the genome isolate is a sister to C. bombacis, but sequence differences and examination of the type material suggest that the genome strain represents an undescribed species of Ceraceosorus, now named Ceraceosorus guamensis sp. nov. (Kijpornyongpan and Aime, 2016). Originally, the genus Ceraceosorus was included in Exobasidiales based on septum ultrastructure and presence of local interaction zones within a host cell (Begerow et al., 2006). However, subsequent molecular sequence analyses do not support the close relationship of Ceraceosorus with Exobasidiales or any other orders in Ustilaginomycotina. Thus, the new order Ceraceosorales was proposed, and its phylogenetic position remains unresolved (Begerow et al., 2006).
The genome sequence of Ceraceosorus guamensis sp. nov. will provide the first whole genome reference sequence for a member of Ceraceosorales. Researchers will use these data in phylogenetic and phylogenomic reconstructions and in comparative genomics studies that seek to elucidate the molecular bases governing production of sexual and anamorphic states and the evolution of phytopathogenicity in Ustilaginomycotina.

References:

Begerow D, Stoll M, Bauer R. 2006. A phylogenetic hypothesis of Ustilaginomycotina based on multiple gene analyses and morphological data. Mycologia 98(6):906–916.

Cunningham J, Bakshi BK, Lentz PL, Gilliam MS. 1967. Two new genera of leaf-parasitic fungi (Basidiomycetidae: Brachybasidiaceae). Mycologia 68(3): 640–654.

Kijpornyongpan T, Aime MC. 2016. Rare or rarely detected? Ceraceosorus guamensis sp. nov.: a second described species of Ceraceosorales and the potential for underdetection of rare lineages with common sampling techniques. Antonie van Leeuwenhoek 109:1127-1139