Characterization of Aspergillus nidulans RabC/Rab6.

ABSTRACT

The Aspergillus nidulans Golgi is not stacked. Early and late Golgi equivalents (GEs) are intermingled but can be resolved by epifluorescence microscopy. RabC, the Aspergillus ortholog of mammalian Rab6, is present across the Golgi, preferentially associated with early GEs near the tip and with late GEs in tip-distal regions. rabCΔ mutants, showing markedly impaired apical extension, have conspicuously fragmented, brefeldin A-insensitive early and late GEs, indicating that the Golgi network organization requires RabC. rabCΔ Golgi fragmentation is paralleled by an increase in early endosome abundance. rabCΔ reduces extracellular levels of the major secretable protease, suggesting that it impairs secretion. Notably, the Spitzenkörper, an apical intracellular structure in which secretory carriers accumulate awaiting fusion with the adjacent plasma membrane (PM), contains RabC. rabCΔ leads to abnormally increased accumulation of carriers, detectable with secretory v-SNARE GFP-SynA and FM4-64, in this structure. VpsT(Vps10) , present across the Golgi, recycles between endosomes and Golgi and is mislocalized to a cytosolic haze by rabCΔ that, in contrast, does not affect SynA recycling between endosomes and the PM, indicating that SynA follows a RabC-independent pathway. tlg2Δ mutants grow normally but are synthetically lethal with rabCΔ, indicating that RabC plays Tlg2-independent roles.