GDP‐mannose transporter contributes to polarity establishment in the filamentous fungus Aspergillus nidulans

Abstract

GDP‐mannose transporters (Gmt) carry nucleotide sugars from the cytosol across the Golgi apparatus membrane in various eukaryotic organisms including plants and a variety of fungi. Some fungal species such as the yeast Saccharomyces cerevisiae express only one Gmt, while others including A. nidulans express paralogues (GmtA and GmtB) whose individual roles have not been elucidated. As in S. cerevisiae GmtA is localized within the Golgi apparatus which in A. nidulans consists of widely separated cisternae, in contrast to the stacked cisternae of animals and plants. Here we show that GmtB localization is congruent with GmtA in mature hyphae. Real‐time reverse transcriptase PCR shows a gradual decrease in GmtA expression during the first 12 hours of germination while GmtB expression remains high and unchanged during this period. Depletion of GmtB by the glucose repressible alcA promoter causes abnormalities in polarized growth, a developmental event that is initiated during the early hours of germination. Taken together these observations suggest that GmtB plays an important role in establishment of polarized growth. Although GmtA and GmtB reside within the same Golgi compartments they appear to perform independent functions at different developmental stages.Funded by Research Corporation, the Merck/AAAS Undergraduate Science Research Program and NSF RUI