The phytopathogenic fungi in the genus Ustilago constitute a significant portion of disease causing agents known as smuts. Species of Ustilago are known to infect all major plant groups, producing pigmented spores which are born in lesions on various plant tissues and exposed to a great deal of solar radiation. The fungal spores are typically pigmented with melanin. Melanin in the spore walls of persistent structures such as spores has been ubiquitously associated with photoprotection. In U. nuda, pigmented spores are more resistant to photokilling by several light regimes; however, under some exposure conditions, the pigmented spores are more sensitive to light. The vegetative cells of some members of the genus Ustilago may also be pigmented due to the accumulation of carotenes (carotenoid hydrocarbons) and/or cytochrome c. Carotene accumulation generally is associated with increased resistance to visible and UV radiation with and without photosensitizers. Cytochrome c accumulation is generally associated with decreased resistance to radiation exposure. Oxygen dependence of this light sensitivity suggests that the cytochrome c (a heme protein) may be a photosensitizing pigment. Carotene accumulation in U. violacea has also been associated with decreased levels of light and chemical induced chromosome damage as measured by mitotic recombination. This review explores cytochrome photosensitization and the photoprotective roles of melanin and carotenes in the genus Ustilago.
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