![]() Butyrolactone I, an inhibitor of eukaryotic cyclin-dependent kinases produced by Aspergillus terreus, increases hyphal branching, sporulation, and production of another secondary metabolite, lovastatin, in this fungus ( 102). The addition of dichloros, an inhibitor of zearalenone synthesis, inhibits the sexual development of this fungus ( 125). Fusarium graminearum produces an estrogenic mycotoxin called zearalenone that enhances perithecial production in F. Other natural products affecting fungal development are better characterized. In most cases, these compounds have not been identified but are presumed to be natural products produced as the mycelia ages. Several studies show that compounds excreted by mycelium can induce asexual and sexual sporulation in other fungi this phenomenon operates across species and genera ( 51, 88). Some secondary metabolites have easily observable effects on morphological differentiation in fungi. nidulans sterigmatocystin mutants indicate that they exhibit a decrease in asexual spore production not detectable by the unaided eye ( 97, 108). It is possible, however, that some natural products have subtle effects on sporulation, as recent studies of A. In addition, some secondary metabolites such as brevianamides A and B produced by Penicillium brevicompactum appear only after conidiation has commenced ( 14). nidulans sterigmatocystin mutants ( 106). Although it was once thought that natural products were essential for sporulation, there are many examples of fungal strains that still sporulate but are deficient in secondary metabolite production, for example, Penicillium urticae patulin mutants ( 103) and A. ![]() In early observations it was noted that the environmental conditions required for sporulation and secondary metabolism were often similar and were more stringent than those for pure vegetative growth ( 21, 51, 103). Secondary metabolite production usually commences late in the growth of the microbe, often upon entering the stationary or resting phase ( 21). Secondary Metabolites That Are Sporogenic Factors We conclude with speculation as to why such a relationship could be of value to the organism. The focus of this review is to provide an overview of the research establishing this connection, and this review covers the progress made to date in elucidating relationships between natural product metabolism and fungal development. Since then, several studies have provided insight into other molecules and pathways that link chemical and morphological differentiation processes in fungi. A critical advance in this regard was the establishment of a G-protein-mediated growth pathway in Aspergillus nidulans that regulates both asexual sporulation and natural product biosynthesis ( 55). Although it has long been noted that biosynthesis of natural products is usually associated with cell differentiation or development, and in fact most secondary metabolites are produced by organisms that exhibit filamentous growth and have a relatively complex morphology, until recently the mechanism of this connection was not clear. Some natural products are deleterious (e.g., mycotoxins), while others are beneficial (e.g., antibiotics) to humankind ( 35). However, interest in these compounds is considerable, as many natural products are of medical, industrial and/or agricultural importance. In many cases, the benefit these compounds confer on the organism is unknown ( 21). In this review we will use the terms interchangeably. In the case of the filamentous fungus Aspergillus nidulans, we review the only described work that genetically links the sporulation of this fungus to the production of the mycotoxin sterigmatocystin through a shared G-protein signaling pathway.įungi are remarkable organisms that readily produce a wide range of natural products often called secondary metabolites. We describe environmental and genetic factors that can influence the production of secondary metabolites. In this review, we describe secondary metabolites produced by fungi that act as sporogenic factors to influence fungal development, are required for spore viability, or are produced at a time in the life cycle that coincides with development. ![]() However, most secondary metabolites are produced after the fungus has completed its initial growth phase and is beginning a stage of development represented by the formation of spores. These compounds are very diverse in structure and perform functions that are not always known. ![]() Filamentous fungi are unique organisms-rivaled only by actinomycetes and plants-in producing a wide range of natural products called secondary metabolites. ![]()
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