Semighini Camile P, Harris Steven D
Plant Science Initiative and Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68588-0660, USA.
Genetics. 2008 Aug;179(4):1919-32. doi: 10.1534/genetics.108.089318. Epub 2008 Aug 9.
In fungal hyphae, apical dominance refers to the suppression of secondary polarity axes in the general vicinity of a growing hyphal tip. The mechanisms underlying apical dominance remain largely undefined, although calcium signaling may play a role. Here, we describe the localized accumulation of reactive oxygen species (ROS) in the apical region of Aspergillus nidulans hyphae. Our analysis of atmA (ATM) and prpA (PARP) mutants reveals a correlation between localized production of ROS and enforcement of apical dominance. We also provide evidence that NADPH oxidase (Nox) or related flavoproteins are responsible for the generation of ROS at hyphal tips and characterize the roles of the potential Nox regulators NoxR, Rac1, and Cdc42 in this process. Notably, our genetic analyses suggest that Rac1 activates Nox, whereas NoxR and Cdc42 may function together in a parallel pathway that regulates Nox localization. Moreover, the latter pathway may also include Bem1, which we propose represents a p40phox analog in fungi. Collectively, our results support a model whereby localized Nox activity generates a pool of ROS that defines a dominant polarity axis at hyphal tips.
在真菌菌丝中，顶端优势是指在生长的菌丝顶端附近对次生极性轴的抑制。尽管钙信号可能起作用，但顶端优势背后的机制在很大程度上仍不明确。在这里，我们描述了构巢曲霉菌丝顶端区域活性氧（ROS）的局部积累。我们对atmA（ATM）和prpA（PARP）突变体的分析揭示了ROS的局部产生与顶端优势的维持之间的相关性。我们还提供证据表明，NADPH氧化酶（Nox）或相关黄素蛋白负责在菌丝顶端产生ROS，并表征了潜在的Nox调节因子NoxR、Rac1和Cdc42在此过程中的作用。值得注意的是，我们的遗传分析表明，Rac1激活Nox，而NoxR和Cdc42可能在调节Nox定位的平行途径中共同发挥作用。此外，后一种途径可能还包括Bem1，我们认为它代表真菌中的一种p40phox类似物。总的来说，我们的结果支持一个模型，即局部的Nox活性产生了一组ROS，这些ROS在菌丝顶端定义了一个主导的极性轴。
