The Molecular Mechanism Of Ethylene Affecting Female Gametophyte Development

Angiosperms undergo the alteration between the diploid sporophytic phase andhaploid gametophytic phase in the life cycle, which is carried out through male andfemale gametogenesis, double fertilization and embryogenesis. In the development offemale gametophyte, the megasporocyte generates only one functionalmegagametophyte after meiosis. After three rounds of nuclear division, it formssuccessively into two-, four-, eight-nucleated embryo sac. At this time, the eightnuclei are divided into four to two sides by the vacuole, and then one of these nucleifrom each side migrates toward the center of the embryo sac and fuse with each other.During and after cellularization, these events result in a seven-celled structureconsisting of three antipodal cells, one two haploid nuclei central cell, two synergidcells, and one egg cell. Before fertilization, the antipodal cells undergo the PCD(programmed cell death).At present, researches on the ethylene signal are studied deeply. When theethylene is in a low concentration level, the unoccupied receptors remain in the activestate and associate with CTR1, which, in turn, represses the downstream signalingpathway. When plants encounter stress conditions, the cascade could be activated andconsequently enhances the production of ethylene. Upon binding ethylene, thereceptor complexes diassociate, and CTR1is released from ER membrane. Ethyleneis transmitted by EIN2and stabilizes the EIN3/EIL1which are mediated by SCFEBF1/2.The EIN3/EIL1is a transcription factor activating ethylene-related gene expressionand perform morphological processes.At present, rare reports referred to the reproductive development affected byethylene. Silencing gene expression of the ethylene-forming enzyme resulted thatmegasporogenesis did not occur and ovules did not reach maturity. Moreover, theethylene take part in the degeneration of synergid cells in mature embryo sac whenfertilizating. ein3eil1double mutant exhibits developmental defects during embryoproper and suspensor formation.This study focused on the SCFEBF1/EBF2mediating the level of EIN3protein in the ethylene singal pathway. We found that ebf1and ebf2single mutant have no obviousphenotype from the appearance. Then, we found the homozygote could not be gainedwhen constructed the ebf1ebf2double mutant. Through the analysis of the genetic, itsignified that EBF1EBF2co-affect the development of female gametophyte.Cytological observation revealed that the megagametophyte development wasasynchronous though they could eventually reach the FG8without staying certainstage. Due to obtaining the ebf1ebf2ein3triple homozygous mutant but not the ebf1ebf2double mutant, we consider that the female gametophye could develope normallyin the triple mutant, which indicated that the ethylene plays a crucial role in femalegametophyte. All above results suggest that activating consistently ethylene pathwaywould affect the development of female gametophyte.