| Popis: |
Fungal biofilm founder cells experience self-generated hypoxia leading to dramatic changes in their cell biology. For example, during Aspergillus nidulans biofilm formation microtubule (MT) disassembly is triggered causing dispersal of EB1(a MT ‘+’ end binding protein) from MT tips. This process is dependent on SrbA, a sterol regulatory element binding transcription factor required for adaptation to hypoxia. We find that SrbA, an ER resident protein prior to activation, is proteolytically activated during early stages of biofilm formation and that its activating proteases are required for normal biofilm cell regulation. In addition to SrbA, the AtrR transcription factor is also found to be required to modulate cellular responses to gaseous signaling during biofilm development. Using co-cultures, we show that cells lacking srbA or atrR are capable of responding to biofilm generated hypoxia and are actually more sensitive to this signal than wild type cells. SrbA is a regulator of ergosterol biosynthetic genes and we find that the levels of seven GFP-tagged Erg proteins differentially accumulate during biofilm formation. This uncovers a complex pattern of regulation with biofilm accumulation of only some Erg proteins being dependent on SrbA with others accumulating to higher levels in its absence. Because different membrane sterols are known to influence cell permeability to gaseous molecules, including oxygen, we propose that differential regulation of ergosterol biosynthetic proteins by SrbA may calibrate the cell’s responsiveness to gaseous signaling which in turn modifies the cell biology of developing biofilm cells. |
