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

• Published in: Molecular plant Vol. 1; no. 4; pp. 586 - 598
• Main Authors: Alandete-Saez, Monica, Ron, Mily, McCormick, Sheila
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01-07-2008; Oxford University Press
• Subjects: Amino Acid Sequence; antisense; Arabidopsis - cytology; Arabidopsis - embryology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Cell Membrane - metabolism; Conserved Sequence; double fertilization; Down-Regulation - genetics; Embryonic Development; Evolution, Molecular; female gametophyte; Gene Expression Regulation, Plant; Membrane Proteins; Molecular Sequence Data; Ovule - cytology; Ovule - metabolism; Phenotype; Plants, Genetically Modified; plasma membrane protein; Pollen Tube - cytology; Pollen Tube - embryology; Pollen Tube - genetics; Pollen Tube - metabolism; PQQ domain; Promoter Regions, Genetic - genetics; Protein Structure, Tertiary; real-time PCR; RNA, Messenger - genetics; RNA, Messenger - metabolism; Seeds - cytology; Seeds - genetics; Selection, Genetic; plasma membrane protein; PQQ domain; real-time PCR; double fertilization; female gametophyte; antisense
• ISSN: 1674-2052; 1752-9867
• DOI: 10.1093/mp/ssn015

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.