Molecular Mechanisms behind the Male-Female Interaction in Fertilization in Higher Plants

In angiosperm, fertilization starts from pollen adhesion, hydration, and germination. Pollen tubes penetrate the stigma, grow into the transmitting tract, and then onto the funiculi by breaking through septums. Finally, one pollen tube is guided to enter micropyle and release two sperm cells that fuse with the egg cell and the central cell respectively to complete fertilization. Notably, the sperm cells of angiosperm, lack of flagellum, are transported into the embryo sac with the help of pollen tubes. It is well received that fertilization is tightly controlled by the male-female interaction at different stages. For example, the pollen tube recognizes and responds to the signals from the ovule so that it can grow into the tiny micropylar opening, and know the proper time to release sperm cells. Meanwhile, sperm cells fuse with the egg and the central cell respectively after signals from both sides are perceived. Therefore, the fertilization depends on the successful recognition and interaction between male and female gametophytes at different developmental stages. This review summarizes recent progress on these interactions during fertilization.