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- Plant Cell
- v.20(11); 2008 Nov
- PMC2613674
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Plant Cell. 2008 Nov; 20(11): 2929.
PMCID: PMC2613674
Nancy A. Eckardt
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See "Maternal Control of Male-Gamete Delivery in Arabidopsis Involves a Putative GPI-Anchored Protein Encoded by the LORELEI Gene" onpage3038.
In flowering plants, male and female gametes are produced in the anther and ovule, respectively. Male gametes are contained within pollen grains, which are released from the anthers at anthesis. After a pollen grain lands on the stigma, male gametes are delivered to the ovule via the pollen tube, which grows rapidly through the sporophytic tissues of the style and into the embryo sac (female gametophyte) within the ovule. The pollen tube grows into one of two synergid cells, which undergoes cell death and degenerates. Two nonmobile sperm cells then are released in close proximity to the egg cell and the central cell, and double fertilization ensues. Signals from the female gametophyte are known to be critical for pollen tube guidance, but the molecular mechanisms involved are not fully understood (Higashiyama and Hamamura, 2008; Punwani and Drews, 2008).
Capron et al. (pages 3038–3049) identify and describe the function of LORELEI (LRE) in Arabidopsis, which encodes a conserved, plant-specific, glucosylphosphatidylinositol-anchored protein (GAP) that is highly expressed in synergid cells of the embryo sac and is involved in signaling between male and female gametophytes.
In German folklore, Lorelei (also Loreley) was a young girl who committed suicide over an unfaithful lover by jumping into the Rhine River from the steep rock that bears her name. According to legend, she became a siren, ever after luring navigators to their deaths in the strong currents that occur at this narrow part of the river. Thus, lorelei is a fitting name for a mutation in Arabidopsis that acts in the female gametophyte to influence navigation of pollen tubes and disrupt the release of sperm cells, thereby preventing fertilization.
In the lre mutant, pollen tubes are guided to the embryo sac, but they do not arrest growth and fail to release the sperm cells. Instead, the pollen tube invades and continues to grow and curl around inside the embryo sac (see figure). In addition, whereas the wild-type embryo sac loses its ability to attract pollen tubes after fertilization is initiated, lre mutant embryo sacs continue to attract additional pollen tubes. Embryo sac development appears normal in the mutant, suggesting a more specialized role for LRE in pollen tube guidance and sperm release.
Figure 1
The lre mutant misguides pollen tubes. Aniline blue staining of an ovule of a lre mutant plant pollinated with wild-type pollen. The pollen tube (arrow) has invaded the central cell (cc) and continued growth, turning back toward the micropylar end (my). ch, chalazial end. Bar = 50 μm.
GAPs are anchored through their C terminus to the extracellular surface of the plasma membrane and have been implicated in a number of membrane signaling and/or recognition processes, including binding of sperm to egg in mammals (Primakoff and Myles, 2007). The lre mutant phenotype is very similar to that of feronia/sirène, which is disrupted in a receptor-like kinase expressed in the filliform apparatus, an extensively thickened and elaborated part of the synergid cell wall (Escobar-Restrepo et al., 2007). The authors speculate that LRE might function in the same pathway as FERONIA as part of a signaling cascade in the synergid cells that ultimately causes cessation of pollen tube growth and release of sperm cells.
References
- Capron, A., Gourgues, M., Neiva, L.S., Faure, J.-E., Berger, F., Pagnussat, G., Krishnan, A., Alvarez-Mejia, C., Vielle-Calzada, J.-P., Lee, Y.-R., Liu, B., and Sundaresan, V. (2008). Maternal control of male-gamete delivery in Arabidopsis involves a putative GPI-anchored protein encoded by the LORELEI gene. Plant Cell 20 3038–3049. [PMC free article] [PubMed] [Google Scholar]
- Escobar-Restrepo, J.M., Huck, N., Kessler, S., Gagliardini, V., Gheyselinck, J., Yang, W.C., and Grossniklaus, U. (2007). The FERONIA receptor-like kinase mediates male-female interactions during pollen tube reception. Science 317 656–660. [PubMed] [Google Scholar]
- Higashiyama, T., and Hamamura, Y. (2008). Gametophytic pollen tube guidance. Sex. Plant Reprod. 21 17–26. [Google Scholar]
- Primakoff, P., and Myles, D.G. (2007). Cell-cell membrane fusion during mammalian fertilization. FEBS Lett. 581 2174–2180. [PubMed] [Google Scholar]
- Punwani, J.A., and Drews, G.N. (2008). Development and function of the synergid cell. Sex. Plant Reprod. 21 7–15. [Google Scholar]
Articles from The Plant Cell are provided here courtesy of Oxford University Press
