AP1Gs Is Critical For Pollen Development And Female-controlled Pollen Tube Reception

Double fertilization is a complex process involving gametophytic development, pollen tube growth, guidance and reception, and gamete recognition and fusion. Pollen tubes perceive female cue to grow directionally toward the embryo sac, whose entrance induces programmed cell death (PCD) of a synergid, which in turn signals pollen tube discharge. Except for surface receptors such as FERONIA (FER), little is known regarding cellular components mediating this process. We report here function of AP1Gs in pollen development and pollen tube reception. AP1Gs encode the ? (G) subunit of the adaptor protein complex 1 (AP1), which is composed of ? (M), ?, ? (G) and ? subunits. AP1 is critical for both anterograde and retrograde trafficking by mediating protein sorting at the trans-Golgi network/early endosome (TGN/EE). The ? (G) subunit is encoded by two highly homologous genes, AP1G1 and AP1G2. We show that functional loss of AP1Gs impaired the dynamic organization and acidification of vacuoles during pollen development, resulting in complete male gametophytic lethality. Pollen tube reception was also compromised such that tubes failed to discharge, resulting in partial female gametophytic lethality. The main results presented in this thesis are as follows:(1) AP1Gs mediated the dynamic organization and acidification of vacuoles play an important role in the male gametophyte development.AP1Gs homozygous double mutants were unable to obtain. Reciprocal crosses indicated that AP1Gs loss of function resulted in complete male gametophytic lethality. Neutral red or BCECF-AM were used to stain mature pollen found that vacuolar acidification of pollen grains was affected by AP1Gs loss-of-function. Through the TEM observation, we found that functional loss of AP1Gs impaired the dynamic vacuolar organization during pollen development.(2) AP1Gs regulate female-controlled pollen tube reception.Reciprocal crosses indicated that AP1Gs loss of function resulted in defective transmission of female gametophytes. Through the experiment confirmed that pollen tube reception was also compromised such that tubes failed to arrest and discharge.The communication between synergid cells and pollen tube is critical for pollen tube reception. This shows that AP1Gs loss of function result in the synergid cell dysfunction.(3) AP1Gs located in the trans-Golgi network/early endosomes (TGN/EE).We generated stable transgenic plants expressing AP1Gs with GFP fusion driven by ProUBQ10. Transgenes fully restored the mutant phenotype in pollen development suggesting functionally intact. Co-labeling analysis showed that AP1Gs was localized at TGN/EE.