Summary Pollen has an extraordinary ability to convert from a dry state to an extremely rapidly growing state. During pollination, pollen receives water and Ca2+ from the contacting pistil, which will be a directional cue for pollen tube germination. The subsequent rapid activation of directional vesicular transport must support the pollen tube growth, but the molecular mechanism leading to this process is largely unknown. We established a luciferase‐based pollination assay to screen genetic mutants defective in the early stage after pollination. We identified a plant‐specific VPS13, Arabidopsis thaliana VPS13a as important for pollen germination, and studied its molecular function. AtVPS13a mutation severely affected pollen germination and lipid droplet discharge from the rough endoplasmic reticulum. Cellular accumulation patterns of AtVPS13a and a secretory vesicle marker were synchronized at the polarized site, with a slight delay to the local Ca2+ elevation. We found a brief Ca2+ spike after initiation of pollen hydration, which may be related to the directional cues for pollen tube emergence. Although this Ca2+ dynamics after pollination was unaffected by the absence of AtVPS13a, the mutant suffered reduced cell wall deposition during pollen germination. AtVPS13a mediates pollen polarization, by regulating proper directional vesicular transport following Ca2+ signaling for directional tube outgrowth.

中文翻译：

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陆地植物特异性 VPS13 介导发芽花粉中的极化囊泡运输


总结 Pollen 具有从干燥状态转变为极速生长状态的非凡能力。在授粉过程中，花粉从接触的雌蕊接收水和 Ca2+ 这将是花粉管萌发的方向线索。随后定向囊泡运输的快速激活必须支持花粉管的生长，但导致这一过程的分子机制在很大程度上是未知的。我们建立了一种基于荧光素酶的授粉测定法，以筛选授粉后早期有缺陷的遗传突变体。我们确定了植物特异性 VPS13 拟南芥 VPS13a 对花粉萌发很重要，并研究了其分子功能。AtVPS13a 突变严重影响花粉萌发和粗面内质网脂滴排出。AtVPS13a 和分泌囊泡标志物的细胞积累模式在极化位点同步，局部 Ca2 + 升高略有延迟。我们发现花粉水合作用开始后出现短暂的 Ca2 + 峰值，这可能与花粉管出现的方向线索有关。尽管授粉后的 Ca 2 + 动力学不受 AtVPS13a 缺失的影响，但突变体在花粉萌发过程中细胞壁沉积减少。AtVPS13a 通过调节 Ca2 + 信号传导后适当的定向囊泡运输以定向管生长来介导花粉极化。