In all eukaryotic cells, Rho-related GTPases (Rho, Rac and Cdc42) are involved in controlling and organizing actin cytoskeleton and thereby controlling polarized cell growth. The genome of A. niger revealed the presence of four Rho-like GTPases (RhoA-D) and single copy Rac1 and CDC forty-two homologs, named RacA and CftA. To asses functions to the different Rho-like GTPases, null mutants have been generated. Of all the disruptants, the racA mutant displayed to most severe growth phenotype and was characterized by a hyperbranching phenotype. In addition, deletion of racA, cftA, rhoB and rhoD resulted in reduced formation of conidia. In general, the growth and morphology of the different disruption strains not severely affected, which could be explained by redundancy. The overlapping function of RacA and CftA was shown by trying to obtain a racA, cftA double deletion mutant. As all primary transformants containing both the racA and the cftA deletion were all heterokaryotic we conclude that the double mutant is lethal. The phenotypic consequences of the loss of racA or cftA on the actin cytoskeleton in germinating spores have been studied in detail. The localization of actin was examined using immunofluorescence in both the wild type and the racA or cftA deletion mutants. Actin patches in the racA mutant showed a severe condensation at the extreme apex at the hyphal tip while both in the cftA mutant and wild type strain a gradient of actin patches towards the tip was observed.
Full conference title:
6th International Aspergillus Meeting
- Asperfest 6 (2009)