• In filamentous fungi, hyphal growth depends on the continuous delivery of vesicles to the growing tips. It is unclear how fast‐growing hyphae coordinate simultaneous cell extension and expansion in the tip cells.
• We have functionally characterized 12 TBC (Tre‐2/Bub2/Cdc16) domain‐containing proteins in Fusarium graminearum. Among them, FgMsb3 is found to regulate hyphal tip expansion and to be required for pathogenicity. The regulatory mechanism of FgMsb3 has been further investigated by genetic, high‐resolution microscopy and high‐throughput co‐immunoprecipitation strategies.
• The FgMsb3 protein localizes at the polarisome and the hyphal apical dome (HAD) where it acts as a GTPase‐activating protein for FgRab8 which is required for apical secretion‐mediated growth and pathogenicity. Deletion of FgMSB3 causes excessive polarized trafficking but blocks the fusion of FgSnc1‐associated vesicles to the plasma membrane. Moreover, we establish that FgSpa2 interacts with FgMsb3, enabling FgMsb3 tethering to the polarisome. Loss of FgSpa2 or other polarisome components (FgBud6 and FgPea2) causes complete shifting of FgMsb3 to the HAD and this affects the polarized growth and pathogenicity of the fungus.
• In summary, we conclude that FgSpa2 regulates FgMsb3–FgRab8 cascade and this is crucial for creating a steady‐state equilibrium that maintains continuous polarized growth and contributes to the pathogenicity of F. graminearum.

中文翻译：

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FgSpa2将FgMsb3（Rab8 GAP）募集到极粒体中，以调节禾谷镰刀菌的极化运输，生长和致病性

• 在丝状真菌中，菌丝的生长取决于囊泡向生长尖端的持续输送。尚不清楚快速增长的菌丝如何协调尖端细胞中细胞的同时扩展和扩展。
• 我们已经在功能上鉴定了禾谷镰刀菌中包含12个TBC（Tre‐2 / Bub2 / Cdc16）域的蛋白质。其中，发现FgMsb3调节菌丝尖端的扩展，并且是致病性所必需的。FgMsb3的调节机制已通过遗传，高分辨率显微镜和高通量免疫共沉淀策略进行了进一步研究。
• FgMsb3蛋白定位在极小体和菌丝顶端圆顶（HAD）处，在其中它充当FgRab8的GTPase激活蛋白，这是顶端分泌介导的生长和致病性所必需的。FgMSB3的缺失会导致过度的极化运输，但会阻止FgSnc1相关囊泡与质膜的融合。此外，我们建立了FgSpa2与FgMsb3相互作用，从而使FgMsb3束缚到极化体的功能。FgSpa2或其他极性体成分（FgBud6和FgPea2）的损失会导致FgMsb3完全转移到HAD，这会影响真菌的极化生长和致病性。
• 总而言之，我们得出的结论是，FgSpa2调节FgMsb3-FgRab8级联，这对于建立稳态平衡，维持连续的极化生长并促进禾谷镰刀菌的致病性至关重要。