Reciprocal regulation between AtFH5-labeled secretory vesicles and PI(4,5)P oscillation at the plasma membrane directs pollen germination.

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P) is known to be an instrumental anionic phospholipid in governing pollen germination and pollen tube growth. However, the precise functions and regulatory mechanisms of PI(4,5)P in pollen polarity establishment and germination remain poorly understood. Our previous studies demonstrated the pivotal involvement of Arabidopsis formin homology 5 (AtFH5)-dependent vesicle trafficking in polarity establishment of pollen. Here, we observed that PI(4,5)P accumulated and oscillated at the prospective germination site, a process closely associated with the rotational movement of AtFH5-labeled vesicles. Disruption of the mobility of AtFH5-labeled vesicles, either through AtFH5 mutation or pharmacological treatment, significantly perturbed the accumulation of PI(4,5)P at the plasma membrane. Subcellular localization and genetic analysis revealed that two phosphatidylinositol 4-phosphate 5-kinases, AtPIP5K1 and AtPIP5K4, are essential for PI(4,5)P oscillation at the germination site prior to pollen germination. Furthermore, we found that the dynamics of AtPIP5K4 depended on the mobility of AtFH5-labeled vesicles and reduced PI(4,5)P in turn disturbed the attachment of AtFH5-labeled secretory vesicles to the plasma membrane. In conclusion, these findings collectively highlight the reciprocal regulation of AtFH5-labeled secretory vesicles and PI(4,5)P oscillations at the plasma membrane, providing critical insights into the molecular mechanism underlying polarity establishment during pollen germination.