Biosynthesis and Functions of Fungal Melanins

• DOI: 10.1146/annurev.py.24.090186.002211
• Publication Date: 2003-07-02T08:44:38Z
• Authors: A A Bell; M H Wheeler
• Keywords: 0303 health sciences; 03 medical and health sciences; 3. Good health

Melanins are dark-brown to black pigments found in animals, plants, and microorganisms. These pigments are not essential for growth and develop­ ment, but rather they enhance the survival and competitive abilities of species in certain environments. The association of melanins with immune responses has been noted for plants (13) and invertebrates (180, 227, 239, 250). Melanin biosynthesis and function have been studied most extensively in animals, primarily because of the association of melanins with skin disorders (25,53, 188) and malignant melanomas (119). Melanins in the eye and inner ear have also received considerable attention because of their interactions with drugs (84). The synthesis of animal melanin from tyrosine by the action of tyrosinase is proven (52, 175, 270). Tyrosinase, the key enzyme in animal melanin synthesis, also occurs and is best characterized in the common mushroom (Agaricus bisporus) and Neurospora crassa (136). Consequently, some researchers have been hasty to conclude that fungal melanins also are derived from tyrosine. The importance of melanins for survival and longevity of fungal propagules has been recognized for many years (126, 235). During the past ten years three additional discoveries have increased interest among plant pathologists in fungal melanins. First, unique pathways for melanin biosynthesis were discovered in both Ascomycotina (16) and Basidiomycotina (234). Second, investigators discovered a new class of fungicides that prevent direct penetra­ tion of plant tissue by inhibiting melanin biosynthesis in appressorial cells (221, 223). Third, phytotoxins were discovered that are shunt products of