Differential gene expression during aerobic germination of Mucor racemosus sporangiospores

Evidence is provided suggesting that several modes of differential gene expression operate concomitantly during the first 60 min of germination of Mucor racemosus sporangiospores under air. Protein synthesis was initiated immediately upon exposure of the spores to nutrient medium and accelerated exponentially throughout the period of observation. All translation during the first 30 min of germination occurred using only preformed stable mRNAs as a template. Analysis of the protein products synthesized in vivo was performed by L-[35S]methionine labeling, one- and two-dimensional polyacrylamide gel electrophoresis, and autoradiography. The population of proteins accumulated during spore formation and present at the time of harvest differed significantly from those proteins synthesized during spore germination. Autoradiographs displayed several proteins synthesized during the former but not the latter morphogenetic process. Conversely, other proteins were synthesized during the first 30 min of germination but not during spore formation, even though the mRNA specifying these proteins must have been synthesized and stored in the dormant spore. A posttranscriptional regulatory mechanism that directs selective translation thus appears to exist in the developing spore. In addition, autoradiographs showed that many proteins, although made throughout the intervals examined, displayed significant changes in their relative rates of synthesis. One gene product exemplified a possible case of post-translational modification during the first hour of sporangiospore germination.