Alternative fruiting pathways in phycomyces.
Developmental distinctions between giant and dwarf fruiting bodies of Phycomyces blakesleeanus (Burgeff) were studied by means of size measurements and growth analyses. Histograms of fruiting body lengths showed a bimodal distribution, with peaks around 0.3 millimeter (dwarfs) and 30 millimeters (giants). Individual cultures contain both giants and dwarfs. Differences between giants and dwarfs appear in the first phase of development; the apex of the giant is tapered, whereas the dwarf apex is dome-shaped. Probable cytological distinctions at this stage are cited in discussion. The dwarfs terminate enlargement upon expansion of the sporangium, thus lacking the subsequent phase of rapid elongation (stage IV) that contributes 90% of the length in the case of giants. It was concluded that P. blakesleeanus maintains two developmental patterns for asexual fruiting, with dwarfs and giants differing radically in growth regulation.
The gene for the heat-shock protein HSP100 is induced by blue light and heat-shock in the fungus Phycomyces blakesleeanus
We cloned and sequenced the Phycomyces hspA gene. The hspA gene product is a 901-amino-acid protein member of the clpB/HSP100 family. HSP100 proteins are ATPases involved in high-temperature tolerance, proteolysis, and protein disaggregation. Phycomyces HSP100 is composed of a domain presumably involved in protein–protein interactions and two ATP-binding domains. The hspA promoter contains three heat-shock elements that are presumably involved in the activation of hspA after heat-shock. In addition, four short sequences are present in the hspA promoter and in the promoter of the photoinducible genes carB and carRA; and these are candidates as binding sites for light-regulated transcription factors. Blue light can increase transcription of the hspA gene 10-fold, with a threshold of 1 J/m2. The threshold for hspA photoactivation is 104 times higher than the thresholds for blue-light regulation of sporangiophore development and photocarotenogenesis, which suggests that there are differences in the photosensory systems for gene photoactivation and mycelial photoresponses. A heat-shock of 30 min at 34°C or 42°C increased hspA gene activity 160-fold. The differences in maximum hspA gene transcription by blue light and heat-shock suggest the presence of different regulatory mechanisms.
The Synthesis and Destruction of Vitamin B(1) by Phycomyces.
In an earlier communication (1) data relative to the in vivo synthesis of vitamin B1, by the isolated pea root have been presented. For a fuller understanding of the physiological economy of the vitamin, some insight also into the modes of disappearance of the substance is indispensable. The accumulated evidence now permits us to present a picture both of in vivo synthesis of the vitamin by Phycomyces Blakesleeanus and of a mechanism by which the vitamin molecule is broken down by the latter organism.