The male gamete membrane protein DMP9/DAU2 is required for double fertilization in flowering plants.

All flowering plants exhibit a unique type of sexual reproduction called 'double fertilization' in which each pollen tube-delivered sperm cell fuses with an egg and a central cell. Proteins that localize to the plasma membrane of gametes regulate one-to-one gamete pairing and fusion between male and female gametes for successful double fertilization. Here, we have identified a membrane protein from Lilium longiflorum generative cells using proteomic analysis and have found that the protein is an ortholog of Arabidopsis DUF679 DOMAIN MEMBRANE PROTEIN 9 (DMP9)/DUO1-ACTIVATED UNKNOWN 2 (DAU2). The flowering plant DMP9 proteins analyzed in this study were predicted to have four transmembrane domains and be specifically expressed in both generative and sperm cells. Knockdown of DMP9 resulted in aborted seeds due to single fertilization of the central cell. Detailed imaging of DMP9-knockdown sperm cells during in vivo and semi-in vitro double fertilization revealed that DMP9 is involved in gamete interaction that leads to correct double fertilization.

Double fertilization on the move.

Double fertilization is a flowering plant mechanism whereby two immotile sperm cells fertilize two different female gametes. One of the two sperm cells fertilizes the egg cell to produce the embryo and the other fertilizes the central cell to produce the endosperm. Despite the biological and agricultural significance of double fertilization, the mechanism remains largely unknown owing to difficulties associated with the embedded structure of female gametes in the maternal tissue. However, molecular genetic approaches combined with novel live-cell imaging techniques have begun to clarify the actual behavior of the sperm cells, which is different from that described by previous hypotheses. In this review article, we discuss the mechanism of double fertilization based on the dynamics of the two sperm cells in Arabidopsis.