In filamentous fungi, the hypha orientation is essential for polarized growth and morphogenesis. The ability to re-orient tip growth in response to environmental cues is critical for the colony survival. Therefore, hyphal tip orientation and tip extension are distinct mechanisms that operate in parallel during filamentous growth. In yeast, the axial growth orientation requires a pathway regulated by Rsr1p/Bud1p, a Ras-like GTPase protein, which determines the axial budding pattern. However, in filamentous fungi the function of the Rsr1/Bud1p gene (krev-1 homolog) has not been completely characterized. In this work, we characterized the phenotype of a homokaryon mutant Bud1p orthologous in Neurospora crassa (△bud-1) and tagged BUD-1 with the green fluorescent protein (GFP) to determine its localization and cell dynamics under confocal microscopy. During spore germination BUD-1 was localized at specific points along the plasma membrane and during germ tube emergence it was located at the tip of the germ tubes. In mature hyphae BUD-1 continued to be located at the cell tip and was also present at sites of branch emergence and at the time of septum formation. The △bud-1 mutant showed a delayed germination, and the orientation of hyphae was somewhat disrupted. Also, the hypha diameter was reduced approximately 37 % with respect to the wild type. The lack of BUD-1 affected the Spitzenkörper (Spk) formation, trajectory, the localization of polarisome components BNI-1 and SPA-2, and the actin cytoskeleton polarization. The results presented here suggest that BUD-1 participates in the establishment of a new polarity axis. It may also mediate the delivery of secretory vesicles for the efficient construction of new plasma membrane and cell wall.

在丝状真菌中，菌丝方向对于极化生长和形态发生至关重要。根据环境提示重新调整尖端生长的能力对于菌落的生存至关重要。因此，菌丝尖端方向和尖端延伸是丝状生长过程中并行运作的不同机制。在酵母中，轴向生长方向需要一条受 Rsr1p/Bud1p（一种 Ras 样 GTP 酶蛋白）调节的途径，它决定轴向出芽模式。然而，在丝状真菌中，Rsr1/Bud1p 基因（ krev-1同源物）的功能尚未完全表征。在这项工作中，我们对粗糙脉孢菌 (Neurospora crassa) 中同源的同核突变体 Bud1p (△bud-1)的表型进行了表征，并用绿色荧光蛋白 (GFP) 标记了 BUD-1，以确定其在共聚焦显微镜下的定位和细胞动力学。在孢子萌发期间，BUD-1 位于质膜上的特定点，在芽管出现期间，它位于芽管的尖端。在成熟的菌丝中，BUD-1 继续位于细胞尖端，并且也存在于分枝出现的部位和隔膜形成时。△ bud-1突变体萌发延迟，菌丝方向有些紊乱。此外，与野生型相比，菌丝直径减少了约 37%。BUD-1 的缺乏会影响 Spitzenkörper (Spk) 的形成、轨迹、极化体成分 BNI-1 和 SPA-2 的定位以及肌动蛋白细胞骨架极化。这里给出的结果表明 BUD-1 参与了新极性轴的建立。它还可以介导分泌囊泡的递送，以有效构建新的质膜和细胞壁。