Department of Cell Biology and Molecular Genetics and the Maryland Agricultural Experiment Station, University of Maryland, College Park, Maryland 20742, USA.
Plant Cell. 2011 Jan;23(1):81-93. doi: 10.1105/tpc.110.080499. Epub 2011 Jan 14.
Flowering plant reproduction requires precise delivery of the sperm cells to the ovule by a pollen tube. Guidance signals from female cells are being identified; however, how pollen responds to those cues is largely unknown. Here, we show that two predicted cation/proton exchangers (CHX) in Arabidopsis thaliana, CHX21 and CHX23, are essential for pollen tube guidance. Male fertility was unchanged in single chx21 or chx23 mutants. However, fertility was impaired in chx21 chx23 double mutant pollen. Wild-type pistils pollinated with a limited number of single and double mutant pollen producing 62% fewer seeds than those pollinated with chx23 single mutant pollen, indicating that chx21 chx23 pollen is severely compromised. Double mutant pollen grains germinated and grew tubes down the transmitting tract, but the tubes failed to turn toward ovules. Furthermore, chx21 chx23 pollen tubes failed to enter the micropyle of excised ovules. Green fluorescent protein-tagged CHX23 driven by its native promoter was localized to the endoplasmic reticulum of pollen tubes. CHX23 mediated K(+) transport, as CHX23 expression in Escherichia coli increased K(+) uptake and growth in a pH-dependent manner. We propose that by modifying localized cation balance and pH, these transporters could affect steps in signal reception and/or transduction that are critical to shifting the axis of polarity and directing pollen growth toward the ovule.
开花植物的繁殖需要精子细胞通过花粉管精确地输送到胚珠。目前正在鉴定来自雌性细胞的导向信号；然而，花粉对这些线索的反应在很大程度上是未知的。在这里，我们表明拟南芥中的两个预测阳离子/质子交换器（CHX），CHX21 和 CHX23，对于花粉管导向是必不可少的。单个 chx21 或 chx23 突变体的雄性育性没有改变。然而，chx21 chx23 双突变体花粉的育性受损。用有限数量的单个和双突变体花粉授粉的野生型柱头产生的种子比用 chx23 单突变体花粉授粉的种子少 62%，这表明 chx21 chx23 花粉严重受损。双突变体花粉粒发芽并在传递道中生长管，但管未能转向胚珠。此外，chx21 chx23 花粉管未能进入切除胚珠的珠孔。由其天然启动子驱动的 GFP 标记的 CHX23 被定位到花粉管的内质网中。CHX23 介导 K(+)运输，因为 CHX23 在大肠杆菌中的表达以 pH 依赖的方式增加了 K(+)摄取和生长。我们提出，通过改变局部阳离子平衡和 pH 值，这些转运蛋白可能会影响信号接收和/或转导的步骤，这些步骤对于改变极性轴并将花粉生长导向胚珠至关重要。
