Department of Plant Pathology, University of Nebraska, Lincoln, NE 68588-0660, USA.
Mol Microbiol. 2012 Jul;85(2):252-70. doi: 10.1111/j.1365-2958.2012.08108.x. Epub 2012 Jun 19.
The yeast bud site selection system represents a paradigm for understanding how fungal cells regulate the formation of a polarity axis. In Saccharomyces cerevisiae, Bud4 and Axl2 are components of the axial bud site marker. To address the possibility that these proteins regulate cellular morphogenesis in filamentous fungi, we have characterized homologues of Bud4 and Axl2 in Aspergillus nidulans. Our results show that Bud4 is involved in septum formation in both hyphae and developing conidiophores. Whereas Axl2 appears to have no obvious role in hyphal growth, it is required for the regulation of phialide morphogenesis during conidiation. In particular, Axl2 localizes to the phialide-spore junction, where it appears to promote the recruitment of septins. Furthermore, the developmental regulators BrlA and AbaA control the expression of Axl2. Additional studies indicate that Axl2 is also involved in the regulation of sexual development, not only in A. nidulans, but also in the phylogenetically unrelated fungus Fusarium graminearum. Our results suggest that Axl2 plays a key role in phialide morphogenesis and/or function during conidiation in the aspergilli.
酵母芽位点选择系统代表了一种理解真菌细胞如何调节极性轴形成的范例。在酿酒酵母中，Bud4 和 Axl2 是轴向芽位点标记物的组成部分。为了研究这些蛋白质是否调节丝状真菌的细胞形态发生，我们在构巢曲霉中鉴定了 Bud4 和 Axl2 的同源物。我们的结果表明，Bud4 参与了菌丝和发育中的分生孢子梗中的隔膜形成。而 Axl2 在菌丝生长中似乎没有明显作用，但它是调节分生孢子形成过程中瓶梗形态发生所必需的。特别是，Axl2 定位于瓶梗-孢子连接处，在该处似乎促进了隔膜蛋白的募集。此外，发育调节剂 BrlA 和 AbaA 控制 Axl2 的表达。进一步的研究表明，Axl2 还参与了性发育的调节，不仅在构巢曲霉中，而且在系统发育上不相关的真菌禾谷镰刀菌中也是如此。我们的结果表明，Axl2 在曲霉属的分生孢子梗形态发生和/或功能调节中起着关键作用。
