Roles of two GDP‐mannose transporters in cell wall stability in the filamentous fungus Aspergillus nidulans

Abstract

In order to identify genes affecting cell wall integrity, we have generated mutant strains of the filamentous fungus Aspergillus nidulans. We have identified two distinct genes (GMT1, GMT2) in one such mutant (R205) that are homologous to the yeast VRG4 GDP‐mannose transporter genes. GDP‐mannose transporters carry nucleotide sugars from the cytosol across the Golgi apparatus membrane in various eukaryotic organisms including plants and a variety of fungi. We have observed punctate patterns of fluorescence of GMT1 and GMT2 GFP chimeras, indicative of Golgi localization in A. nidulans. Cloned GMT1 and GMT2 complement hypersensitivity to the chitin binding agent calcofluor white in strain R205, and ameliorate hyper‐branching and septation abnormalities R205 displays under normal growth conditions. GMT1 in R205 contains a genetic mutation that causes an A315P amino acid substitution, and the amino acid sequence of GMT2 in R205 is identical to wild type. However, both GMT1 and GMT2 appear to be essential. These findings suggest that GMT1 and GMT2 are involved in cell wall maintenance in A. nidulans.Funded by Research Corporation and the Merck/AAAS Undergraduate Science Research Program