Aspergillus nidulans alpha-1,3 glucanase (mutanase), mutA, is expressed during sexual development and mobilizes mutan.

We established a subtractive cDNA library of Aspergillus nidulans to identify differentially expressed genes during sexual development. One of the clones displayed homology to fungal alpha-1,3 glucanases (mutanase). Since alpha-1,3 glucan is considered the main reserve material accumulated during vegetative growth as a cell wall component and consumed during sexual development, we analyzed this gene in detail. The gene, mutA, is disrupted by three introns and encodes a putative protein of 48 kDa molecular mass with a signal peptide for secretion at the N terminus. The deduced protein displays amino acids 24-42% identical to mutanases of other fungi. A proposed mutan binding domain characterized in, e.g., Penicillium is not present in A. nidulans. Mutanase transcript and GFP reporter analysis in A. nidulans revealed specific induction of the gene during sexual development in Hülle cells. To study the role of mutA during sexual differentiation, we constructed a mutA deletion strain. Although degradation of mutan was affected in this strain, it was still able to form cleistothecia at a number similar to that of wildtype. These results suggest that additional carbon sources are available during sexual development.

Genetic evidence for a microtubule-destabilizing effect of conventional kinesin and analysis of its consequences for the control of nuclear distribution in Aspergillus nidulans.

Conventional kinesin is a microtubule-dependent motor protein believed to be involved in a variety of intracellular transport processes. In filamentous fungi, conventional kinesin has been implicated in different processes, such as vesicle migration, polarized growth, nuclear distribution, mitochondrial movement and vacuole formation. To gain further insights into the functions of this kinesin motor, we identified and characterized the conventional kinesin gene, kinA, of the established model organism Aspergillus nidulans. Disruption of the gene leads to a reduced growth rate and a nuclear positioning defect, resulting in nuclear cluster formation. These clusters are mobile and display a dynamic behaviour. The mutant phenotypes are pronounced at 37 degrees C, but rescued at 25 degrees C. The hyphal growth rate at 25 degrees C was even higher than that of the wild type at the same temperature. In addition, kinesin-deficient strains were less sensitive to the microtubule destabilizing drug benomyl, and disruption of conventional kinesin suppressed the cold sensitivity of an alpha-tubulin mutation (tubA4). These results suggest that conventional kinesin of A. nidulans plays a role in cytoskeletal dynamics, by destabilizing microtubules. This new role of conventional kinesin in microtubule stability could explain the various phenotypes observed in different fungi.

A Pcl-like cyclin of Aspergillus nidulans is transcriptionally activated by developmental regulators and is involved in sporulation.

The filamentous fungus Aspergillus nidulans reproduces asexually through the formation of spores on a multicellular aerial structure, called a conidiophore. A key regulator of asexual development is the TFIIIA-type zinc finger containing transcriptional activator Bristle (BRLA). Besides BRLA, the transcription factor ABAA, which is located downstream of BRLA in the developmental regulation cascade, is necessary to direct later gene expression during sporulation. We isolated a new developmental mutant and identified a leaky brlA mutation and the mutated Saccharomyces cerevisiae cyclin homologue pclA, both contributing to the developmental phenotype of the mutant. pclA was found to be 10-fold transcriptionally upregulated during conidiation, and a pclA deletion strain was reduced three- to fivefold in production of conidia. Expression of pclA was strongly induced by ectopic expression of brlA or abaA under conidiation-suppressing conditions, indicating a direct role for brlA and abaA in pclA regulation. PCLA is homologous to yeast Pcl cyclins, which interact with the Pho85 cyclin-dependent kinase. Although interaction with a PSTAIRE kinase was shown in vivo, PCLA function during sporulation was independent of the A. nidulans Pho85 homologue PHOA. Besides the developmental regulation, pclA expression was cell cycle dependent with peak transcript levels in S phase. Our findings suggest a role for PCLA in mediating cell cycle events during late stages of sporulation.