Allergen of the MonthdUstilago maydis There are over 800 species of smut. Ustilago is a genus containing about two hundred species of parasitic smuts on grasses.1,2 U. maydis is a parasite of maize, and like corn, native to Mexico. It is dimorphic, existing as single-cell yeast on dead plant matter, or as a pathogenic filamentous form produced by mating. Cell fusion and pathogenicity is controlled by two mating loci: a and b. The a locus encodes a pheromone and receptor for cell recognition. The b locus controls pathogen development. Signal cascade is through a MAPK pathway.1 A white to dark grey gall forms on the corn or the stem, and which may be quite large. However, these galls, called huitlacoche, are considered a delicacy in Mexico and may be sold for a greater price than unaffected corn.1,3 U. esculenta is parasitic on wild rice, Zizania, but the spores have been used in Japan as paint in traditional lacquering.4 Ustilago spore counts can be considerable, even accounting for a quarter of the total fungal count in Delhi.5e7 Seasonal rises occur during harvesting.6 Ustilago spores have been found second in number to Cladosporium in the air of a hospital ward.8 Wittich reported both rhinitis and asthma from Ustilago, followed by other case reports as well.4,9,10 Sensitization to Ustilago has been reported in asthmatic or rhinitis patients between 14% and 52%.11,12 Occupational hypersensitivity pneumonitis is reported with exposure to U. esculenta.4 Ustilago species are in the phylum Basidiomycota, class Ustilagomycetes, subclass Ustilaginomycetidae, order Ustilaginales, and family Ustilaginaceae.1,3 The entire genome of U. maydis has been sequenced. Prior work revealed no antigenic crossreactivity between Basidiomycetes and Deuteromycetes.13 There are no characterized allergens identified for Ustilago. However, there appears to be homology between Malassezia sympodialis allergen Mala s 1and the U. maydis protein Q4P4P8.14 Smuts and rusts do not grow on typical agar, but can be grown on appropriate media. Colonies grow slowly, maturing in 3 weeks, appearing moist and yeast-like with creamy yellow color. U. maydis spores are 7-10 mm in diameter, spheroidal, inaperturate, and olive brown in color. Walls are uniformly thick. Surface is prominently echinate.5,15 Text by Richard W. Weber, M.D. Photography by Estelle Levetin, PhD, Biological Science, University of Tulsa

References [1] DeSanno C, Lizzo S, Paoletti D, Salzillo J, Bartholomew K. Ustilago. http:// microbewiki.kenyon.edu/index.php/Ustilago (10/19/13). [2] Kendrick B. The Fifth Kingdom. Waterloo, Ontario, Canada, Mycologue Publications 1985:98e99. [3] Spooner B. Ustilago maydis (maize smut). http://www.kew.org/plantsfungi/Ustilago-maydis.htm (10/19/13). [4] Yoshida K, Suga M, Yamasaki H, et al. Hypersensitivity pneumonitis induced by a smut fungus Ustilago esculenta. Thorax. 1996;51:650e651.

[5] Bassett IJ, Crompton CW, Parmalee JA. An atlas of airborne pollen grains and common fungus spores of Canada. Hull, Quebec. Printing and Publishing, Supply and Services Canada, 1978:299e301. [6] González Glez Minero FJ, Candau P, González Glez Romano ML, Romero F. A study of the aeromycoflora of Cádiz: relationship to anthropogenic activity. J Investig Allergol Clin Immunol. 1992;2:211e215. [7] Gupta SK, Pereira BMJ, Singh AB. Survey of airborne culturable and nonculturable fungi at different sites in Delhi metropolis. As Pac J Allergy Immunol. 1993;11:19e28. [8] Tormo Molino R, Gonzalo Garijo MA, Muñoz Rodriguez AF, Silva Palacios I. Pollen and spores in the air of a hospital out-patient ward. Allergol Immunopathol. 2002;30:232e238. [9] Wittich FW, Stackman FC. A case of respiratory allergy due to inhalation of grain smuts. J Allergy. 1937;8:189. [10] Wittich FW. Further observations on allergy to smuts. Lancet. 1939;59: 382e388. [11] Giannini EH, Northey WT, Leathers CR. The allergenic significance of certain fungi rarely reported as allergens. Ann Allergy. 1975;35: 372e376. [12] Santilli J Jr., Rockwell WJ, Collins RP. Individual patterns of immediate skin reactivity to mold extracts. Ann Allergy. 1990;65:454e458. [13] Lopez M, Salvaggio J, Butcher B. Allergenicity and immunogenicity of Basidiomycetes. J Allergy Clin Immunol. 1976;57:480e488. [14] Vilhelmsson M, Zargari A, Crameri R, et al. Crystal structure of the major Malassezia sympodialis allergen Mala s 1 reveals a b-propeller fold: a novel fold among allergens. J Mol Biol. 2007;369:1079e1086. [15] Kapp RO. How to Know Pollen and Spores. Dubuque, IA, Wm. C. Brown Co., 1969:63.

Reprints: Richard W. Weber, M.D. National Jewish Health 1400 Jackson Street Room J326 Denver, CO 80206