ANXUR1 and 2, Sister Genes to FERONIA/SIRENE, Are Male Factors for Coordinated Fertilization

In sexual reproduction, proper communication and cooperation between male and female organs and tissues are essential for male and female gametes to unite. In flowering plants, female sporophytic tissues and gametophytes direct a male pollen tube toward an egg apparatus, which consists of an egg cell and two synergid cells. The cell-cell communication between the pollen tube and the egg apparatus makes the tip of pollen tube rupture to release the sperm cell. To detect male factors involved in this communication, we screened mutants of receptor-like kinases expressed in pollen tubes and characterized ANXUR1 (ANX1) and ANXUR2 (ANX2) genes. Here we report that pollen tubes of anx1/anx2 mutants ruptured before arriving at the egg apparatus, suggesting that ANX1 and ANX2 are male factors controlling pollen tube behavior by directing rupture at proper timing. Furthermore, ANX1 and ANX2 were the most closely related paralogs of a female factor, FERONIA/SIRENE, controlling pollen tube behavior expressed in synergid cells. Our findings show that the coordinated behaviors of female and male reproductive apparatuses are regulated by these sister genes, whose duplication might play a role in the evolution of the fertilization system in flowering plants.