The fluffy Gene of Neurospora crassa Is Necessary and Sufficient to Induce Conidiophore Development

The fl (fluffy) gene of Neurospora crassa encodes a binuclear zinc cluster protein that regulates the production of asexual spores called macroconidia. Two other genes, acon-2 and acon-3, play major roles in controlling development. fl is induced specifically in differentiating tissue during conidiation and acon-2 plays a role in this induction. We examined the function of fl by manipulating its level of expression in wild-type and developmental mutant strains. Increasing expression of fl from a heterologous promoter in a wild-type genetic background is sufficient to induce conidiophore development. Elevated expression of fl leads to induction of development of the acon-2 mutant in nitrogen-starved cultures, but does not bypass the conidiation defect of the acon-3 mutant. These findings indicate that fl acts downstream of acon-2 and upstream of acon-3 in regulating gene expression during development. The eas, con-6, and con-10 genes are induced at different times during development. Morphological changes induced by artificially elevated fl expression in the absence of environmental cues were correlated with increased expression of eas, but not con-6 or con-10. Thus, although inappropriate expression of fl in vegetative hyphae is sufficient to induce conidial morphogenesis, complete reconstitution of development leading to the formation of mature conidia may require environmental signals to regulate fl activity and/or appropriate induction of fl expression in the developing conidiophore.

A Pcl-Like Cyclin of Aspergillus nidulans Is Transcriptionally Activated by Developmental Regulators and Is Involved in Sporulation

ABSTRACT The filamentous fungus Aspergillus nidulansreproduces 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 mutatedSaccharomyces cerevisiae cyclin homologuepclA, both contributing to the developmental phenotype of the mutant. pclA was found to be 10-fold transcriptionally upregulated during conidiation, and apclA deletion strain was reduced three- to fivefold in production of conidia. Expression of pclA was strongly induced by ectopic expression of brlA orabaA under conidiation-suppressing conditions, indicating a direct role for brlA andabaA 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 theA. 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.