Submitted to: Molecular Plant
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2008
Publication Date: 5/25/2008
Publication URL: http://mplant.oxfordjournals.org/cgi/reprint/ssn015v1
Citation: Alandete-Saez, M., Ron, M., McCormick, S.M. 2008. GEX3, Expressed in the Male Gametophyte and in the Egg Cell of Arabidopsis thaliana, Is Essential for Micropylar Pollen Tube Guidance and Plays a Role during Early Embryogenesis. Molecular Plant. 1(4):586-598. Interpretive Summary: The GEX3 gene encodes a protein that is located on the surface of cells. The protein is expressed in the sperm and in the egg. When the gene is either over-expressed or down-regulated, the plants have a defect in pollen tube guidance, and the problem is on the female side. These results suggest that the egg is important for pollen tube guidance.
Technical Abstract: Double fertilization in flowering plants occurs when the two sperm cells, carried by the pollen tube, are released in a synergid cell of the embryo sac and then fertilize the egg and the central cell. Proteins on the surfaces of the sperm, egg, central, and synergid cells might be important for guidance and recognition/fusion of the gametes. Here, we present functional analyses of Arabidopsis GEX3, which encodes a plasma membrane-localized protein that has homologs in other plants. GEX3 is expressed in both the vegetative and sperm cells of the male gametophyte and in the egg cell of the female gametophyte. Transgenic lines in which GEX3 was down-regulated or overexpressed, using the Arabidopsis GEX2 promoter, had reduced seed set. Reciprocal crosses and imaging after pollination with a reporter line showed that, in both cases, the defect causing reduced seed set occurred in the female. In the antisense lines, micropylar pollen tube guidance failed. In the overexpression lines, fertilization of mutant ovules was mostly blocked because pollen tube guidance failed, although, occasionally, non-viable embryos were formed. We conclude that properly regulated expression of GEX3 in the egg cell of Arabidopsis is essential for pollen tube guidance.