Gene expression inMucordimorphism

Abstract

An ongoing dialectic has concerned the relative importance of differential gene expression versus the pattern of new wall deposition in Mucor dimorphism. Numerous physiological processes and enzyme activities have been observed in flux during morphogenesis, but a causal link to dimorphism has been infrequently demonstrated. Very few of the proteins that are conspicuous in two-dimensional polyacrylamide gel electrophoresis are specific to cell morphology or significantly change in amount during morphogenesis. Cyclic AMP, putrescine, S-adenosylmethionine, and enzymes governing their intracellular concentrations show patterns of change that consistently correlate with morphogenesis. The expression of RAS proteins and translation elongation factor-1α activity during morphogenesis are regulated at the level of transcription and post-translational methylation, respectively. Wall chemistry is very similar in both morphologies, but wall deposition is isodiametric in yeasts and vectorial in hyphae. Electron microscopy shows patterns of apparent exocytosis that are generalized in the former and apical in the latter. Research on other dimorphic fungi, including Saccharomyces cerevisiae, suggests an involvement of cytoskeletal proteins and a family of GTP-linked protein kinases in directing polar growth. Some of these elements, which may be controlled quite distal from the genes encoding them, have been demonstrated in Mucor spp., while others are the subject of ongoing investigations. Key words: Mucor, dimorphism, morphogenesis, gene expression, yeasts, hyphae.