Roles of the Aspergillus nidulans UDP-galactofuranose transporter, UgtA in hyphal morphogenesis, cell wall architecture, conidiation, and drug sensitivity

Galactofuranose (Galf) is the 5-member-ring form of galactose found in the walls of fungi including Aspergillus, but not in mammals. UDP-galactofuranose mutase (UgmA, ANID\_3112.1) generates UDP-Galf from UDP-galactopyranose (6-member ring form). UgmA-GFP is cytoplasmic, so the UDP-Galf residues it produces must be transported into an endomembrane compartment prior to incorporation into cell wall components. ANID\_3113.1 (which we call UgtA) was identified as being likely to encode the A. nidulans UDP-Galf transporter, based on its high amino acid sequence identity with A. fumigatus GlfB. The ugtA Delta phenotype resembled that of ugmA Delta, which had compact colonies, wide, highly branched hyphae, and reduced sporulation. Like ugmA Delta, the ugtA Delta hyphal walls were threefold thicker than wild type strains (but different in appearance in TEM), and accumulated exogenous material in liquid culture. AfglfB restored wild type growth in the ugtA Delta strain, showing that these genes have homologous function. Immunostaining with EBA2 showed that ugtA Delta hyphae and conidiophores lacked Galf, which was restored in the AfglfB-complemented strain. Unlike wild type and ugmA Delta strains, some ugtA Delta metulae produced triplets of phialides, rather than pairs. Compared to wild type strains, spore production for ugtA Delta was reduced to 1\%, and spore germination was reduced to half. UgtA-GFP had a punctate distribution in hyphae, phialides, and young spores. Notably, the ugtA Delta strain was significantly more sensitive than wild type to Caspofungin, which inhibits beta-glucan synthesis, suggesting that drugs that could be developed to target UgtA function would be useful in combination antifungal therapy. (C) 2011 Elsevier Inc. All rights reserved.