Functional versatility of synergid cells in plant reproduction.

In flowering plants (angiosperms), the Polygonum-type embryo sac accounts for approximately 70% of the female gametophytes. It contains three antipodal cells, one central cell, one egg cell, and two synergid cells. Apart from the female gamete cells, the synergid cells play a key role in sexual reproduction. This review traces the origin and research history of synergid cells and summarizes the latest research progress in understanding their core functions in the angiosperm-specific siphonogamy. In particular, we discuss the diverse functions of synergid cells in pollen tube guidance, pollen tube reception, and fertilization recovery. We highlight how angiosperms guarantee fertility by regulating the timing and sequence of the synergid cell degeneration and persistence. Moreover, we discuss important unresolved scientific questions in synergid cell research and provide an outlook on future research directions.