Isolation of a gene required for programmed initiation of development by Aspergillus nidulans.

Abstract

In contrast to many other cases in microbial development, Aspergillus nidulans conidiophore production initiates primarily as a programmed part of the life cycle rather than as a response to nutrient deprivation.Mutations in the acoD locus result in "fluffy" colonies that appear to grow faster than the wild type and proliferate as undifferentiated masses of vegetative cells. We show that unlike wild-type strains, acoD deletion mutants are unable to make conidiophores under optimal growth conditions but can be induced to conidiate when growth is nutritionally limited. The requirement for acoD in conidiophore development occurs prior to activation of brL4, a primary regulator of development. The acoD transcript is present both in vegetative hyphae prior to developmental induction and in developing cultures. However, the effects of acoD mutations are detectable only after developmental induction. We propose that acoD activity is primarily controlled at the posttranscriptional level and that it is required to direct developmentally specific changes that bring about growth inhibition and activation of brUA expression to result in conidiophore development.

Regulation of Conidiation by Light in Aspergillus nidulans

“…The genes fluG and flbA-C encode developmental regulators that act upstream of brlA, and their deletion reduces the expression of brlA, resulting in aconidial, fluffy phenotypes (Adams et al 1992(Adams et al , 1998Wieser et al 1994). Thus, our next question was whether these regulatory genes were also induced by light.…”

The Aspergillus nidulans fluG gene is required for production of an extracellular developmental signal and is related to prokaryotic glutamine synthetase I.

“…Mutations in all of these genes result in fluffy colonies that proliferate as undifferentiated masses of vegetative mycelia. How ever, when fluG~ mutants are grown under nutrient limiting conditions, this requirement is partially over come, and some limited conidiation results (Adams et al 1992). This observation led us to suggest that brlA can be activated in more than one way.…”

“…When fluG mutants are grown on complete medium they produce a large mass of undifferentiated aerial mycelia giving the colony a fluffy appearance (Adams et al 1992). Figure 1 shows that when a fluG deletion mu tant that also carried a spore-color mutation resulting in yellow-spored conidiophores {yA2) was grown on com plete medium next to a green-spored wild-type strain, yellow-spored conidiophores were produced at the inter face between the two colonies (Fig.…”

“…The DNA sequence of the fluG genomic region (Adams et al 1992) and a nearly full-length fluG cDNA clone (including the entire coding region) was determined and is presented in Figure 2. The cDNA sequence contains a single long open reading frame that is predicted to en code a 864-amino-acid polypeptide with a molecular mass of 96,389 daltons.…”

“…Activation of brlA expression likely represents a major control point in the conidiation pathway because forced expression of brlA at any time during the life cy cle is sufficient to activate development of simple conid iophores that produce viable spores (Adams et al 1988). We showed previously that fluG (formerly called acoD), flbA, and several other genes are required for the pro grammed switch from mycelial growth to activation of brlA expression and conidiophore development (Adams et al 1992;B. Lee and T. Adams, in prep.).…”