Isolation and physical characterization of three essential conidiation genes from Aspergillus nidulans.

Abstract

We cloned and characterized three genes from Aspergillus nidulans, designated brUA, abaA, and wetA, whose activities are required to complete different stages of conidiophore development. Inactivation of these genes causes major abnormalities in conidiophore morphology and prevents expression of many unrelated, developmentally regulated genes, without affecting the expression of nonregulated genes. The three genes code for poly(A)+ RNAs that begin to accumulate at different times during conidiation. The briA-and abaA-encoded RNAs accumulate specifically in cells of the conidiophore. The weL4-encoded RNA accumulates in mature conidia. Inactivation of the brL4 gene prevents expression of the abaA and wet4 genes, whereas inactivation of the abaA gene prevents expression of the wetA gene. Our results confirm genetic predictions as to the temporal and spatial patterns of expression of these genes and demonstrate that these patterns are specified at the level of RNA accumulation.The mitotically derived spores, or conidia, of the ascomycetous fungus Aspergillus nidulans are produced on multicellular structures called conidiophores (14). Scanning electron microscope images of developing conidiophores are shown in Fig. 1. Under appropriate conditions, certain hyphal elements (Fig. 1A) differentiate into thick-walled foot cells and produce aerial stalk initials (Fig. 1B). The stalks grow away from the substratum for a defined period of time, growth stops, and a multinucleated vesicle forms by swelling of the stalk apex (Fig. 1C). A layer of primary sterigmata, or metullae, is formed on the surface of the vesicle by budding (Fig. 1D), and a single nucleus enters each cell. The metullae undergo a single division to produce a layer of secondary sporogenous sterigmata, or phialides (Fig. 1E). Conidia are formed following mitotic divisions of the phialide nucleus (Fig. 1F). After each division, one daughter nucleus is retained within the phialide, where it continues to undergo mitoses. The other daughter nucleus enters the tip of the phialide which buds off to form a conidium. As this process continues, previously formed conidia are displaced by newly formed conidia, producing a long chain of clonally derived spores at various stages of maturity. We have previously shown that conidiophore development in A. nidulans involves the stage-and cell-type-specific expression of approximately 1,000 different genes (15).The genetic mechanisms that control the differentiation and spatial organization of conidiophore cells have been investigated by Clutterbuck and co-workers, who isolated a variety of mutant strains with altered conidiophore morphologies (1,2,4,10). Many of the mutations they studied are conidiophore specific, having little or no detectable effect on hyphal growth or sexual reproduction. The mechanisms by which the genes identified by these mutations bring about the orderly assembly of the asexual reproductive apparatus are unknown.Mutations in three genes cause major developmental defects and thus are of particular inter...

The genetics of conidiophore pigmentation in Aspergillus nidulans.

“…It has been demonstrated that transcription of ivoB is regulated, directly or indirectly, by brlA (Adams et al 1988;Birse & Clutterbuck, 1990 b). There is also good evidence that brlA encodes a DNA-binding protein; it has been sequenced and the inferred peptide contains a zincfinger DNA-binding motif (Boylan et al, 1987). Furthermore, mis-scheduled expression of brlA is sufficient to activate transcription of many genes characteristic of later conidiophore development, including ivoB (Adams et al, 1988).…”

NsdD Is a Key Repressor of Asexual Development inAspergillus nidulans

“…The deletion of sfgA causes hyperactive conidiation and eliminates the need for fluG in conidiation and ST production. These led us to propose that the developmental transition from vegetative growth in A. nidulans occurs via removal of the negative regulator SfgA, which inhibits precocious activation of brlA during proliferation, thereby allowing proper vegetative growth.During conidiogenesis, the spatial and temporal expression of brlA, abaA, and wetA is tightly controlled (Boylan et al 1987;Mirabito et al 1989;Adams et al 1998;Ni et al 2010). For instance, transcripts of brlA and abaA specifically accumulate during the early-to-middle phases of conidiophore formation and quickly disappear upon the formation of conidia.…”

“…During conidiogenesis, the spatial and temporal expression of brlA, abaA, and wetA is tightly controlled (Boylan et al 1987;Mirabito et al 1989;Adams et al 1998;Ni et al 2010). For instance, transcripts of brlA and abaA specifically accumulate during the early-to-middle phases of conidiophore formation and quickly disappear upon the formation of conidia.…”

Identification of novel genes associated with conidiation in Beauveria bassiana with suppression subtractive hybridization

“…The Aspergillus nidulans brlA gene, which is essential for conidiation, encodes a zinc finger protein. BRLA is directly involved in regulating the transcription of other developmentally related genes (Boylan et al 1987, Marshall and Timberlake 1991, Chang and Timberlake1993, Andrianopolus and Timberlake 1994, Adams et al 1998. The A39 sequence and brlA shared high similarity within the conserved domain of the zinc finger protein.…”