swoP1 (swollen cell) and podB1 (polarity defective) mutations in Aspergillus nidulans interfere with establishment and maintenance of polarity. At restrictive temperatures, conidia of swoP1 may swell to approximately 1.5 times the normal diameter, produce abnormally wide hyphae and/or establish multiple points of polarity, which grow isotropically before arrest. Conidia of podB1 never establish polarity at restrictive temperatures. Cell walls of both strains are as thick as 1 μm (TEM) compared to ca. 0.04 μm at 28C, and the cytoplasm contains numerous irregular membrane structures. Genes complementing the mutations of swoP1 and podB1 have strong sequence homology to COG4 (AN7462) and COG2 (AN8226), respectively. Sequencing of the respective loci reveals point mutations causing truncations near the C-terminus. In mammals and yeast, COG2 and COG4 are part of a multi-protein structure called the COG (conserved oligomeric Golgi) complex associated with retrograde transport within the Golgi apparatus. To provide evidence for a COG function of AN7462 and AN8226, we used a high-copy AMA1 plasmid to overexpress the COG homologues of A. nidulans COG1-4, COG6, COG7, as well as the functionally-related homologues YPT1 (Rab GTPase) and HOC1 (mannosyl transferase). High copy expression of COG2 corrected the swoP1 phenotype while the remaining proteins did not. High copy expression of COG3 and COG4 corrected the podB1 phenotype while the remaining proteins did not. Collectively, these results support a conclusion that the SwoP and PodB proteins function in a common complex including a predicted COG3, which is consistent with the structure of the "œA lobe" of yeast and mammalian COG models.
Full conference title:
6th International Aspergillus Meeting
- Asperfest 6 (2009)