ABSTRACT Aspergillus flavus contaminates agricultural products worldwide with carcinogenic aflatoxins that pose a serious health risk to humans and animals. The fungus survives adverse environmental conditions through production of sclerotia. When fertilized by a compatible conidium of an opposite mating type, a sclerotium transforms into a stroma within which ascocarps, asci, and ascospores are formed. However, the transition from a sclerotium to a stroma during sexual reproduction in A. flavus is not well understood. Early events during the interaction between sexually compatible strains of A. flavus were visualized using conidia of a green fluorescent protein (GFP)-labeled MAT1-1 strain and sclerotia of an mCherry-labeled MAT1-2 strain. Both conidia and sclerotia of transformed strains germinated to produce hyphae within 24 h of incubation. Hyphal growth of these two strains produced what appeared to be a network of interlocking hyphal strands that were observed at the base of the mCherry-labeled sclerotia (i.e., region in contact with agar surface) after 72 h of incubation. At 5 wk following incubation, intracellular green-fluorescent hyphal strands were observed within the stromatal matrix of the mCherry-labeled strain. Scanning electron microscopy of stromata from a high- and low-fertility cross and unmated sclerotia was used to visualize the formation and development of sexual structures within the stromatal and sclerotial matrices, starting at the time of crossing and thereafter every 2 wk until 8 wk of incubation. Morphological differences between sclerotia and stromata became apparent at 4 wk of incubation. Internal hyphae and croziers were detected inside multiple ascocarps that developed within the stromatal matrix of the high-fertility cross but were not detected in the matrix of the low-fertility cross or the unmated sclerotia. At 6 to 8 wk of incubation, hyphal tips produced numerous asci, each containing one to eight ascospores that emerged out of an ascus following the breakdown of the ascus wall. These observations broaden our knowledge of early events during sexual reproduction and suggest that hyphae from the conidium-producing strain may be involved in the early stages of sexual reproduction in A. flavus. When combined with omics data, these findings could be useful in further exploration of the molecular and biochemical mechanisms underlying sexual reproduction in A. flavus.

中文翻译：

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黄曲霉有性繁殖过程中基质内形态变化的表征

摘要 黄曲霉通过致癌黄曲霉毒素污染全球农产品，对人类和动物构成严重健康风险。真菌通过产生菌核在不利的环境条件下存活。当由相反交配类型的相容分生孢子受精时，菌核转化为基质，在基质中形成子囊果、子囊和子囊孢子。然而，黄曲霉在有性繁殖过程中从菌核到基质的转变尚不清楚。使用绿色荧光蛋白 (GFP) 标记的 MAT1-1 菌株的分生孢子和 mCherry 标记的 MAT1-2 菌株的菌核，可以可视化黄曲霉性相容性菌株之间相互作用期间的早期事件。转化菌株的分生孢子和菌核在孵育 24 小时内萌发产生菌丝。这两个菌株的菌丝生长产生了似乎是一个互锁的菌丝链网络，在孵育 72 小时后在 mCherry 标记的菌核（即与琼脂表面接触的区域）的底部观察到。孵育后第 5 周，在 mCherry 标记菌株的基质基质内观察到细胞内绿色荧光菌丝链。来自高和低生育力交叉和未交配的菌核的基质的扫描电子显微镜用于可视化基质和菌核基质内有性结构的形成和发展，从交叉时开始，此后每 2 周到 8 周孵化。菌核和基质之间的形态差异在孵育 4 周时变得明显。在高生育力杂交的基质基质内发育的多个子囊果内检测到内部菌丝和croziers，但在低生育力杂交的基质或未交配的菌核中未检测到。在培养 6 到 8 周时，菌丝尖端产生大量子囊，每个子囊包含 1 到 8 个子囊孢子，这些子囊孢子在子囊壁破裂后从子囊中出现。这些观察结果拓宽了我们对有性繁殖早期事件的了解，并表明来自产分生孢子菌株的菌丝可能参与了黄曲霉有性繁殖的早期阶段。当与组学数据相结合时，这些发现可能有助于进一步探索黄曲霉有性生殖的分子和生化机制。