Tip growth is an extreme form of polarized cell expansion that occurs in all eukaryotic kingdoms to generate highly elongated tubular cells with specialized functions, including fungal hyphae, animal neurons, plant pollen tubes, and root hairs (RHs). RHs are tubular structures that protrude from the root epidermis to facilitate water and nutrient uptake, microbial interactions, and plant anchorage. RH tip growth requires polarized vesicle targeting and active exocytosis at apical growth sites. However, how apical exocytosis is spatially and temporally controlled during tip growth remains elusive. Here, we report that the Qa-Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) SYP121 acts as an effector of Rho of Plants 2 (ROP2), mediating the regulation of RH tip growth. We show that active ROP2 promotes SYP121 targeting to the apical plasma membrane. Moreover, ROP2 directly interacts with SYP121 and promotes the interaction between SYP121 and the R-SNARE VAMP722 to form a SNARE complex, probably by facilitating the release of the Sec1/Munc18 protein SEC11, which suppresses the function of SYP121. Thus, the ROP2-SYP121 pathway facilitates exocytic trafficking during RH tip growth. Our study uncovers a direct link between an ROP GTPase and vesicular trafficking and a new mechanism for the control of apical exocytosis, whereby ROP GTPase signaling spatially regulates SNARE complex assembly and the polar distribution of a Q-SNARE.

尖端生长是极化细胞扩张的一种极端形式，它发生在所有真核生物界中，以产生具有特殊功能的高度细长的管状细胞，包括真菌菌丝、动物神经元、植物花粉管和根毛 (RH)。RH 是从根表皮突出的管状结构，以促进水分和养分吸收、微生物相互作用和植物锚定。RH 尖端生长需要极化囊泡靶向和顶端生长部位的主动胞吐作用。然而，在尖端生长过程中，如何在空间和时间上控制顶端胞吐作用仍然难以捉摸。在这里，我们报告了 Qa-Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) SYP121 作为 Rho of Plants 2 (ROP2) 的效应器，介导 RH 尖端生长的调节。我们显示活性 ROP2 促进 SYP121 靶向顶端质膜。此外，ROP2 直接与 SYP121 相互作用，促进 SYP121 与 R-SNARE VAMP722 相互作用形成 SNARE 复合物，可能是通过促进 Sec1/Munc18 蛋白 SEC11 的释放，从而抑制 SYP121 的功能。因此，ROP2-SYP121 通路促进了 RH 尖端生长过程中的胞吐运输。我们的研究揭示了 ROP GTPase 与囊泡运输之间的直接联系，以及一种控制顶端胞吐作用的新机制，即 ROP GTPase 信号在空间上调节 SNARE 复合物组装和 Q-SNARE 的极性分布。