Fertilization is the central event in the life cycle of all sexual organisms and occurs when male and female gametes fuse. Flowering plants (including major crops like corn, rice, and soybean) undergo double fertilization: one sperm fuses with the egg cell to form an embryo and another sperm fuses with the central cell to produce endosperm, a specialized tissue that provides metabolic support for the embryo. These events lead to formation of seeds, the basis of the human diet. The molecular mechanisms responsible for the fusion of gametes are not well understood in any organism. The hap2 mutation completely blocks the ability of sperm to fertilize female gametes in Arabidopsis thaliana, a flowering plant that is an excellent genetic model organism. The HAP2 gene encodes a protein that is only expressed in sperm cells and is predicted to span the sperm plasma membrane. The hypothesis of this project is that the HAP2 protein on the sperm surface interacts with another protein on the female gamete and that this interaction is required for gamete fusion. The experiments proposed here are designed to define the role of HAP2 in fertilization, determine the topology of HAP2 on sperm membranes, identify egg and central cell-expressed proteins that interact with HAP2 and define HAP2 sequences that are critical for its function. These studies have the potential to uncover molecular mechanisms critical for fertilization in many organisms including humans. This project will provide interdisciplinary training for a graduate student and several undergraduates recruited from Brown University and The Community College of Rhode Island. In addition, novel educational materials and laboratory exercises will be developed and distributed to educators.
