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IN BRIEF
LORELEI: Guiding the Fate of Male Gametes
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 nnn) identify and
describe the function of LORELEI (LRE) in
Arabidopsis, which encodes a conserved,
plant-specific, glucosylphosphatidylinositolanchored 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.
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.
Nancy A. Eckardt
News and Reviews Editor
[email protected]
REFERENCES
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 ¼
50 mm.
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 during double fertilization in Arabidopsis
involves a putative GPI-anchored protein
encoded by the LORELEI gene. Plant Cell
20: nnn.
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.
Higashiyama, T., and Hamamura, Y. (2008).
Gametophytic pollen tube guidance. Sex. Plant
Reprod. 21: 17–26.
Primakoff, P., and Myles, D.G. (2007). Cell-cell
membrane fusion during mammalian fertilization. FEBS Lett. 581: 2174–2180.
Punwani, J.A., and Drews, G.N. (2008). Development and function of the synergid cell.
Sex. Plant Reprod. 21: 7–15.
www.plantcell.org/cgi/doi/10.1105/tpc.108.201112
The Plant Cell Preview, www.aspb.org ª 2008 American Society of Plant Biologists
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LORELEI: Guiding the Fate of Male Gametes
Nancy A. Eckardt
Plant Cell; originally published online November 21, 2008;
DOI 10.1105/tpc.108.201112
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