An Analysis of the Arabidopsis Pollen Transcriptome

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Abstract
BACKGROUND In flowering plants, male gametogenesis occurs in the anthers. The division of a diploid sporogenic cell results in two cells with very different fates—the tapetal initial cell and the pollen mother cell. The tapetum, which supplies nutrients to the developing pollen, is formed from the tapetal initial cell while the pollen mother cell undergoes meiosis to produce mi- crospores, a tetrad of haploid cells. Subsequently, micro- spores undergo an asymmetric mitotic division, creating a smaller generative cell enclosed in the larger vege- tative cell. The vegetative cell then forms the pollen tube while the generative cell undergoes mitosis once again to form the two sperm cells (tricellular pollen grain). At what point this second division occurs is species specific. In the majority of flowering plants, it is during pollen tube growth. However, in the case of the crucifers and grasses, the division occurs while the pollen grain is still in the anther. In most species, pollen is released in a partially hydrated state and becomes fully hydrated upon contact with the stigma. Thevegetativecell extendsthe pollen tube by tipgrowth, ultimately delivering the sperm cells to the embryo sac and completing the pollen development process. Pol- len tube extension does not involve cell division, only cell elongation. Because of this, pollen grains have become a model system for studying cell growth. Pollen must be able to rapidly produce the proteins necessary for germination and pollen tube growth. Due to its specialized function, pollen would be ex- pected to have a different transcriptome than sporo- phytic tissues; thus, the identification of the uniquely expressed genes in pollen will aid in further studies of pollen germination.