Transcript Cell-cell communication during double fertilization

Cell-cell
communication
during double
fertilization
BL 5400
Generalized preparatory events in
double fertilization
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Generation of embryo sac/ megagametophyte
from haploid functional megaspore
 Eight nucleate immature female gametophyte
(FG) generation
 Migration of these cells according to their cell
fate
Contd…
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Formation of egg apparatus consists of
egg nucleus and flanked by two synergids
Antipodal cells formation and degeneration
by Programmed Cell Death (PCD)
Polar nuclei migrate towards EA and fuse
before/after fertilization
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Generalized model of key cell-cell communication events before and after fertilization in angiosperms
a.
b.
c.
Embryo sac maturation and guidance molecules for male gametophyte
Events towards fertilization by the two male gametophytes
Karyogamy, cell-cell signaling and cell division
Genetic studies
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Ds transposon insertion lines identified 130
mutants having defects in FG development
Thirty-three lines were defective in embryo
sac maturation
Defective fertilization in 18 lines. Of these
lines defective pollen tube attraction (6),
unfertilized mature ovum (12)
Development (Pagnussat et al,
2005)
Problems in identification of genes
in haploid cells (FG/MG)
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Mutations in housekeeping genes could arrest
development and nuclear division
 Gene redundancy in plant genomes
 One member of gene family can fully or partially
complement another member in the same gene
family by which important genes can be
overlooked
Important mutants identifies key
factors during fertilization
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ZmEA1 gene product encodes a small
protein that contains predicted TM domain
secreted by egg apparatus guides the
pollen tube at micropylar end
Science (Marton et al, 2005)
Female control of male gamete delivery during
fertilization
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First evidence of female control over male gametophyte
In the pistils of sirene (srn) mutant, half of the embryo
sacs remained unfertilized
Srn embryo sacs could have been structurally or
physiologically incapable of correctly receiving pollen
tube
Embryo sac could not have emitted signals which can
arrest pollen tube growth or discharge
A. Unfertilized embryo sac in a srn/SRN pistil
B. sirene embryo sac penetrated by a pollen tube
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C. Abnormal growth of pollen tube in srn mutant
D. Wild type embryo sac penetrated by pollen tube,
with a degenerated synergid cell (dsy)
Current Biology (Rotman et al,
2003)
A. Wild type embryo sac penetrated
by a pollen tube reaches
B. Tangled structure in embryo sac
(pollen tube outgrowth)
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C. Two pollen tubes penetration in the
micropyle of an ovule
D. Interpretative scheme for the serene
phenotype
sirene affects the pollen tube morphology within the embryo sac
Current Biology (Rotman et al,
2003)
Arabidopsis mutant feronia disrupts the female
gametophytic control pollen tube reception
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Mutant identified from the Ds tagged population and
screened for reduced seed set, obtained feronia as a
result of loss-of-function mutation affecting female
gametophyte
Embryo sac does not arrest the pollen tube growth in
feronia mutants and sperm cells are not released
Supernumerary pollen tubes were attracted by feronia
mutant embryo sac
Synergid specification and degeneration in feronia
normal?
Development (Huck etal, 2003)
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A.
WT FG mature
B.
Fertilized WT showing elongated zygote and free endosperm
C.
Unfertilized feronia after 24 HAP
D.
WT ovule after fertilization
E.
Feronia PT invadingmicropylar area
F.
GUS activity in WT
G.
Feronia mutant GUS activity
H.
& I. invading PT enters central cell
J. Formation of free nuclear endosperm after PT has invaded the FG
Development (Huck et al, 2003)
magatama mutant delays the FG
development
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Wandering and polyspermy phenotype of pollen
tubes of maa1 and maa3 mutants
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Delay in the fusion of polar cell nuclei thereby
maintaining seven-celled eight nuclear state
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Schematic drawing of the monogamy model explain how one pollen tube
(PT) but not more, grows and fertilizes a female gametophyte (FG). Pol, pollen grain;
Sp, stigmatic papilla; tt, transmitting tissue; MMR, male-male repulsion; FS, funiculus
guidance signal; MS, micropylar signal
Development (Shimizu &
Okada, 2000)
Cell-cell communication
highlights
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The maize gene, ZmES1-4 is specifically expressed in FG and downregulated immediately after fertilization
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Several genes expressed immediately after fertilization shows
homology to anti-microbial proteins, indicating that they are signaling
molecules
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Several proteases have been reported to be expressed after
fertilization to degrade the signals by those extra-cellular proteases
thereby preventing polyspermy
References
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Dresselhaus T. (2006). Current Opinion in Plant Biology 9:41-47
 Huck N., Moore J. M., Federer M., Grossniklaus U. (2003) Development 130:
2149-2159
 Rotman N., Rozier F., Boavida L., Dumas C., Berger F., Faure, J-E. (2003)
Current Biology 13: 432-436
 Shimizu K.K. and Okada K. (2000). Development 127:4511-4518