Lee B N, Adams T H
Department of Biology, Texas A & M University, College Station, 77843, USA.
EMBO J. 1996 Jan 15;15(2):299-309.
The Aspergillus nidulans fluG gene is necessary for the synthesis of a small diffusible factor that is required for the endogenously regulated induction of asexual sporulation that takes place during the development of an air-exposed colony. Previous work established that FluG is present at nearly constant levels throughout the Aspergillus life cycle, leading to the hypothesis that FluG factor is constitutively produced and development initiates after its concentration surpasses a fixed threshold. Here we show that overexpression of fluG can overcome the developmental block normally imposed on vegetative cells in submerged culture and leads to the formation of complex conidiophores that are remarkably similar to wild-tye conidiophores made by air- exposed colonies. This fluG-induced sporulation requires the activities of other early developmental regulatory genes including, flA, flB, flC, flD, flE, and brlA. The requirement for flbA in fluG-induced sporulation is particularly interesting because overexpression of flbA can also induce sporulation in submerged culture and this flbA activity requires fluG. The interdependence of fluG and flbA activities suggests a close relationship between the products of these two genes in controlling conidiophore development. In addition to the endogenous sporulation signal provided by fluG, several environmental factors, including air exposure, carbon or nitrogen stress, and increased osmolarity, can influence developmental activation. We demonstrate that each of these signals requires the brlA beta gene, but not brlA alpha, to initiate conidiophore development. We present a model to account for the complex genetic and environmental controls leading to the activation of brlA beta and sporulation.
构巢曲霉fluG基因对于一种小的可扩散因子的合成是必需的，这种因子是气生菌落发育过程中内源性调控的无性孢子形成诱导所必需的。先前的研究表明，在构巢曲霉的整个生命周期中，FluG的水平几乎保持恒定，这导致了一种假说，即FluG因子是组成型产生的，并且在其浓度超过固定阈值后发育开始。在这里，我们表明，fluG的过表达可以克服通常施加于深层培养中营养细胞的发育阻滞，并导致形成与气生菌落产生的野生型分生孢子梗非常相似的复杂分生孢子梗。这种由fluG诱导的孢子形成需要其他早期发育调控基因的活性，包括flA、flB、flC、flD、flE和brlA。flbA在fluG诱导的孢子形成中的需求特别有趣，因为flbA的过表达也可以在深层培养中诱导孢子形成，并且这种flbA活性需要fluG。fluG和flbA活性的相互依赖性表明这两个基因的产物在控制分生孢子梗发育方面存在密切关系。除了由fluG提供的内源性孢子形成信号外，几种环境因素，包括暴露于空气中、碳或氮胁迫以及渗透压增加，都可以影响发育激活。我们证明，这些信号中的每一个都需要brlAβ基因，但不需要brlAα基因来启动分生孢子梗的发育。我们提出了一个模型来解释导致brlAβ激活和孢子形成的复杂遗传和环境控制。
