Abstract：
Phosphatidylinositol 4-phosphate 5-kinase (PIP5K) is a key enzyme producing the signaling lipid phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2 ] in eukaryotes. Although PIP5K genes are reported to be involved in pollen tube germination and growth, the essential roles of PIP5K in these processes remain unclear. Here, we performed a comprehensive genetic analysis of the Arabidopsis thaliana PIP5K4, PIP5K5, and PIP5K6 genes and revealed that their redundant function is essential for pollen germination. Pollen with the pip5k4pip5k5pip5k6 triple mutation was sterile, while pollen germination efficiency and pollen tube growth were reduced in the pip5k6 single mutant and further reduced in the pip5k4pip5k6 and pip5k5pip5k6 double mutants. YFP-fusion proteins, PIP5K4-YFP, PIP5K5-YFP, and PIP5K6-YFP, which could rescue the sterility of the triple mutant pollen, preferentially localized to the tricolpate aperture area and the future germination site on the plasma membrane prior to germination. Triple mutant pollen grains under the germination condition, in which spatiotemporal localization of the PtdIns(4,5)P2 fluorescent marker protein 2xmCHERRY-2xPHPLC as seen in the wild type was abolished, exhibited swelling and rupture of the pollen wall, but neither the conspicuous protruding site nor site-specific deposition of cell wall materials for germination. These data indicate that PIP5K4-6 and their product PtdIns(4,5)P2 are essential for pollen germination, possibly through the establishment of the germination polarity in a pollen grain.
摘要：
磷脂酰肌醇4-磷酸5-激酶（PIP5K）是真核生物中产生信号脂质磷脂酰肌醇4,5-双磷酸[PtdIns（4,5）P2]的关键酶。尽管据报道PIP5K基因参与花粉管的萌发和生长，PIP5K在这些过程中的重要作用尚不清楚.这里,我们对拟南芥PIP5K4，PIP5K5和PIP5K6基因进行了全面的遗传分析，并揭示了它们的冗余功能对于花粉萌发至关重要。具有pip5k4pip5k5pip5k6三重突变的花粉是不育的，而花粉萌发效率和花粉管生长在pip5k6单突变体中降低，在pip5k4pip5k6和pip5pip5k6双突变体中进一步降低。YFP-融合蛋白,PIP5K4-YFP,PIP5K5-YFP,和PIP5K6-YFP，可以挽救三重突变花粉的不育，在发芽之前，优先定位在质膜上的三酚酸盐孔径区域和未来的发芽部位。三突变体花粉粒在发芽条件下，其中PtdIns（4,5）P2荧光标记蛋白2xmCHERRY-2xPHPLC的时空定位在野生型中被废除，表现出花粉壁的膨胀和破裂，但既不是显眼的突出部位，也不是用于发芽的细胞壁材料的特定部位沉积。这些数据表明，PIP5K4-6及其产物PtdIns(4,5)P2是花粉萌发所必需的，可能是通过建立花粉粒中的发芽极性。
