RabA4 subfamily proteins, the key regulators of intracellular transport, are vital for tip growth of plant polar cells, but their unique distribution in the apical zone and role in vesicle targeting and trafficking in the tips remain poorly understood. Here, we found that loss of Arabidopsis (Arabidopsis thaliana) AMINOPHOSPHOLIPID ATPASE 3 (ALA3) function resulted in a marked decrease in YFP-RabA4b/ RFP-RabA4d- and FM4-64-labeled vesicles from the inverted-cone zone of the pollen tube tip, misdistribution of certain intramembrane compartment markers, and an obvious increase in pollen tube width. Additionally, we revealed that phosphatidylserine (PS) was abundant in the inverted-cone zone of the apical pollen tube in wild-type Arabidopsis and was mainly colocalized with the trans-Golgi network/early endosome, certain post-Golgi compartments, and the plasma membrane. Loss of ALA3 function resulted in loss of polar localization of apical PS and significantly decreased PS distribution, suggesting that ALA3 is a key regulator for establishing and maintaining the polar localization of apical PS in pollen tubes. We further demonstrated that certain Rab GTPases colocalized with PS in vivo and bound to PS in vitro. Moreover, ALA3 and RabA4d collectively regulated pollen tube growth genetically. Thus, we propose that the tip-localized PS established by ALA3 is crucial for Rab GTPase-mediated vesicle targeting/trafficking and polar growth of pollen tubes in Arabidopsis.

RabA4 亚家族蛋白是细胞内运输的关键调节因子，对于植物极细胞的尖端生长至关重要，但它们在顶端区的独特分布以及在尖端囊泡靶向和运输中的作用仍然知之甚少。在这里，我们发现拟南芥 ( Arabidopsis thaliana ) 氨基磷脂酶 3 (ALA3) 功能的丧失导致花粉管倒锥区中 YFP-RabA4b/ RFP-RabA4d 和 FM4-64 标记的囊泡显着减少尖端，某些膜内标记的错误分布，以及花粉管宽度的明显增加。此外，我们还发现，野生型拟南芥顶端花粉管的倒锥区中富含磷脂酰丝氨酸（PS），并且主要与反高尔基体网络/早期内体、某些后高尔基体区室和血浆共定位。膜。 ALA3功能的丧失导致顶端PS极性定位的丧失并显着减少PS分布，这表明ALA3是花粉管中建立和维持顶端PS极性定位的关键调节因子。我们进一步证明某些 Rab GTPases 在体内与 PS 共定位并在体外与 PS 结合。此外，ALA3和RabA4d在遗传上共同调节花粉管的生长。因此，我们认为 ALA3 建立的尖端定位 PS 对于拟南芥中 Rab GTPase 介导的囊泡靶向/运输和花粉管的极性生长至关重要。