ABSTRACT

Fungal morphologies (cellular structures) are extremely diverse, and morphogenesis (the transition between different structural morphotypes) is a complex process. "Dimorphic" is a somewhat arbitrary designation for fungi that display two predominant morphotypes. This classification is simplified, because frequently there may be more than one type of cell structure displayed by a morphotype, e.g., the mold morphotype may include mycelia (also tenned "hyphae") and conidia (spores), and there may be intennediate morphologic structures, such as genn tubes and pseudohyphae. Although morphogenesis is an example of developmental changes, it is distinct from the life cycles displayed by other organisms such as some protozoan parasites. In general, there is no evidence that cycling between different morphotypes is obligatory for fungi. Instead, dimorphism is a mechanism some fungi have evolved to survive and proliferate in different environments. It follows that these fungi are capable of sensing environmental signals and of transducing these signals to activate regulatory cascades leading to morphogenesis, and moreover that different morphotypes are adaptively suited to different environments. The rapidly burgeoning field of fungal signal transduction, which clearly interfaces with morphogenesis and plays a role in controlling relevant gene expression, is covered in Chapter 6.