The Molecular Mechanism Of RPG1 Regulating The Pollen Wall Pattern Formation In Arabidopsis

Angiosperms develop a complex structure of exine that protects the normal development of pollen grain. Pollen plays a crucial role in male gametophyte development, which is surrounded by the pollen wall. Pollen wall is composed of exine, intine and tryphine. The particular pattern of pollen wall is crucial for pollen protection.RPG1/SWEET8, encodes a plasma membrane localized sugar transporter, is a key gene controlling pollen wall pattern formation. The transcripts of RPG1/SWEET8 are highly accumulated in both microsporocyte and tapetum during early pollen development. The knockout of RPG1/SWEET8 gene leads to the reduction of primexine deposition which gives rise to the defect of pollen wall pattern and male sterility in rpg1/sweet8. But in the late developmental stage, the fertility of rpg1/sweet8 can be recovered. In our study, the RPG1-GFP was used to track the expression pattern of RPG1/SWEET8. RPG1/SWEET8 was identified to be localized on the plasma membrane of microsporocyte, microspore and mature pollen grain, but not tapetum, which indicates that the primexine formation is dependent on the microsporocypte. rpg1/sweet8 is a mutant that shows male sterility in early developmental stage and fully fertility in late stage. When place under low temperature, the fertility of rpg1/sweet8 was interestedly recovered in early developmental stage. Pollen grains were also normally produced in the low temperature treated mutant. Further cytological observation showed that different from rpg1/sweet8 under normal temperature, the primexine deposition was also recovered under low temperature, and pollen wall pattern was also partially recovered to be established. The measurement of pollen growth showed pollen grew slower under low temperature than that under normal temperature. The similar results were also observed in the late developmental stage pollen grains. Therefore, the slow pollen development could help recover the primexine deposition in rpg1/sweet8 mutant. Besides, the rpg1.rpg2 double mutant exhibited harder fertility recovery than rpg1/sweet8 mutant under low temperature, indicating that even if the slow pollen development is helpful to the primexine deposition, the defect in sugar transporting is sufficient to affect primexine deposition.