Fig. 4

The hypothesized stages of autophagy-mediated gongylidium development. A An unknown mechanism (potentially starvation mediated by ant pruning (Bass and Cherrett 1996)) triggers initial hyphal widening. As a hypha elongates, its nuclei (orange circles) tend to be located near the hyphal tip. B Mediated primarily by an autophagic process, a large vacuole expands via the fusion of newly-formed double membrane vesicles called autophagosomes (blue membraned vesicles) that sequester material present in the cytosol like glycogen (black and gray aggregates) and damaged mitochondria (brown indented ovals). This process is indicated by the proliferation of endoplasmic reticulum membranes (blue membranes around nuclei) that produce autophagosomes. C The fusion of autophagosomes into vacuoles mediates apical bulb swelling and halts further apical growth by excluding nuclei from the hyphal tip. If stray nuclei remain at the hyphal tip, intercalary bulbs are formed. D This process repeats in up to hundreds of adjacent hyphae that become tangled to form the staphyla