1. Cell-cell communication during double fertilization

2. Generalized preparatory events in double fertilization
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

3. Contd…
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

4. Generalized model of key cell-cell communication events before and after fertilization in angiosperms
Embryo sac maturation and guidance molecules for male gametophyte
Events towards fertilization by the two male gametophytes
Karyogamy, cell-cell signaling and cell division

5. Development (Pagnussat et al, 2005)
Genetic studies
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)

6. Problems in identification of genes in haploid cells (FG/MG)
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

7. Important mutants identifies key factors during fertilization
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)

8. Female control of male gamete delivery during fertilization
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

9. Current Biology (Rotman et al, 2003)
A. Unfertilized embryo sac in a srn/SRN pistil
B. sirene embryo sac penetrated by a pollen tube
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)

10. 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)
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)

11. Development (Huck etal, 2003)
Arabidopsis mutant feronia disrupts the female gametophytic control pollen tube reception
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 feroniamutants 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)

12. Development (Huck et al, 2003)
WT FG mature
Fertilized WT showing elongated zygote and free endosperm
Unfertilized feronia after 24 HAP
WT ovule after fertilization
Feronia PT invadingmicropylar area
GUS activity in WT
Feronia mutant GUS activity
& I. invading PT enters central cell
J. Formation of free nuclear endosperm after PT has invaded the FG
Development (Huck et al, 2003)

13. magatama mutant delays the FG development
Wandering and polyspermy phenotype of pollen tubes of maa1 and maa3 mutants
Delay in the fusion of polar cell nuclei thereby maintaining seven-celled eight nuclear state

14. Development (Shimizu & Okada, 2000)
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)

15. Cell-cell communication highlights
The maize gene, ZmES1-4 is specifically expressed in FG and down-regulated immediately after fertilization
Several genes expressed immediately after fertilization shows homology to anti-microbial proteins, indicating that they are signaling molecules
Several proteases have been reported to be expressed after fertilization to degrade the signals by those extra-cellular proteases thereby preventing polyspermy

16. References
Dresselhaus T. (2006). Current Opinion in Plant Biology 9:41-47
Huck N., Moore J. M., Federer M., Grossniklaus U. (2003) Development 130:
Rotman N., Rozier F., Boavida L., Dumas C., Berger F., Faure, J-E. (2003) Current Biology 13:
Shimizu K.K. and Okada K. (2000). Development 127: