Vacuolar CBL-CIPK12 Ca2+-Sensor-Kinase Complexes Are Required for Polarized Pollen Tube Growth
Vacuolar CBL-CIPK12 Ca2+-Sensor-Kinase Complexes Are Required for Polarized Pollen Tube Growth
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DOI：
10.1016/j.cub.2015.03.053
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发表时间：
2015-06
期刊：
影响因子：
9.2
通讯作者：
Leonie Steinhorst;Anette Mähs;T. Ischebeck;Chunxia Zhang;Xinxin Zhang;S. Arendt;Stefanie Schültke;I. Heilmann;J. Kudla
中科院分区：
文献类型：
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作者：
Leonie Steinhorst;Anette Mähs;T. Ischebeck;Chunxia Zhang;Xinxin Zhang;S. Arendt;Stefanie Schültke;I. Heilmann;J. Kudla
极化顶端生长是神经元轴突、真菌菌丝、植物根毛和花粉管等特化真核细胞的基本过程。在花粉管中，聚焦于尖端的振荡钙离子梯度控制着离子通量、小泡运输和细胞骨架动力学，以确保适当的极化细胞生长[1，2]。虽然液泡钙信号在保卫细胞动力学等细胞运动中起着至关重要的作用[3-5]，但它对极化生长的贡献仍有待确定。在这里，我们确定了两个密切相关的液泡膜定位的钙感受器蛋白CBL2和CBL3，它们是液泡动力学和极化花粉管生长的关键调节因子。CBL2或CBL3在拟南芥和烟草花粉管中的过表达影响了液泡形态、花粉萌发和花粉管的生长，但不改变肌动蛋白的组织、PI(4，5)P的分布或以尖端为中心的钙振荡。同样，单个钙离子感受器和cbl2/cbl3双突变体的功能丧失，在体内外都表现出花粉管生长受阻。两个Ca~(2+)感受器都与激酶CIPK12相互作用，在这种相互作用下，该蛋白从细胞质转移到液泡膜。此外，CIPK12的过度表达导致严重的空泡表型，CIPK12功能的丧失导致极地生长障碍。值得注意的是，CBL2或CBL3与CIPK12共表达导致依赖磷酸化的、大规模增强的空泡膨胀，并进一步扰乱极地生长。综上所述，这些发现确定了液泡和液泡钙信号在极化尖端生长中的重要作用。我们认为，钙激活的CBL2/3-CIPK12复合体的活性忠实地平衡，发挥了使高等植物花粉管快速生长的基本功能。
Polarized tip growth is a fundamental process of specialized eukaryotic cells like neuronal axons, fungal hyphae, and plant root hairs and pollen tubes. In pollen tubes, a tip-focused oscillating Ca2+gradient governs ions fluxes, vesicle transport, and cytoskeleton dynamics to ensure proper polarized cell growth [1, 2]. While a crucial role of vacuolar Ca2+signaling is established for cellular movements like guard cell dynamics [3–5], its contribution to polarized growth remains to be defined. Here we identified the two closely related tonoplast-localized Ca2+-sensor proteins CBL2 and CBL3 as crucial regulators of vacuolar dynamics and polarized pollen tube growth. Overexpression of CBL2 or CBL3 inArabidopsisand tobacco pollen tubes affected vacuolar morphology, pollen germination, and tube growth, but did not alter actin organization, PI(4,5)P2distribution, or tip-focused Ca2+oscillations. Similarly, loss of function of each single Ca2+sensor andcbl2/cbl3double mutants exhibited impaired pollen tube growth in vitro and in vivo. Both Ca2+sensors interacted with the kinase CIPK12, which translocated from the cytoplasm to the vacuolar membrane upon this interaction. Also, overexpression of CIPK12 induced severe vacuolar phenotypes, and loss of function ofCIPK12lead to impairment of polar growth. Remarkably, co-expression of CBL2 or CBL3 with CIPK12 resulted in a phosphorylation-dependent, massively enhanced vacuolar inflation and further disruption of polar growth. Together, these findings identify an essential role of the vacuole and vacuolar Ca2+signaling for polarized tip growth. We propose that a faithfully balanced activity of Ca2+-activated CBL2/3-CIPK12 complexes fulfills fundamental functions to enable the fast growth of pollen tubes in higher plants.