| Aspergillus species synthesize an array of structurally different metabolites that utilize a common polyketide pattern of biosynthesis. In many cases, the selective advantage conferred by the metabolite to the producing organism is poorly understood. In contrast, polyketide derived fungal spore pigments are thought to provide protection against environmental stresses. The structural characterization of novel materials in which a specific function has been assigned may shed light on the evolutionary development of other related metabolites.; The Aspergillus asexual and sexual processes of sporulation usually culminates in the production of either yellow, green, red, or black pigmented conidia and ascospores. For example, A. nidulans produces two types of pigmented spores: green, asexually-generated conidia (produced atop conidiophores) and red sexually-generated ascospores (produced within cleistothecia). In contrast, A. parasiticus produces only one type: green pigmented asexual conidia. The green pigment is positively correlated with increased resistance to UV light while the function of the red pigment is unknown.; We have determined the structure of an orange, putative green pigment intermediate produced by A. parasiticus, to be a linear hydroxylated naphtho-{dollar}gamma{dollar}-pyrone (parasperone A). Based on the structure of parasperone A and a comparison to model compounds, we propose it is a polyketide derived material. In addition, evidence suggests that the corresponding pigment produced by A. nidulans, is structurally similar.; We have also determined the structure of the major A. nidulans ascospore pigment to be a novel bisanthraquinone (ascoquinone A). Based on its structure and a comparison to model compounds, it is also a polyketide derived material. The similarity between the sexual spore pigments and norsolorinic acid, the first stable intermediate in the aflatoxin pathway, may indicate an evolutionary relationship.; In addition, we have characterized an aromatic para-hydroxylation activity exhibited by A. parasiticus. Deuterium retention experiments suggested that the activity was a cytochrome P-450 monooxygenase. Diploid complementation tests revealed that at least two genetic loci are required and parasexual analysis indicated that they are linked. The broad substrate specificity of the activity as well as the observation that it is induced by phytoalexins suggests that it may function in vivo to detoxify the chemical defensive mechanisms of some plants. |
