Fertilization in flowering plants requires a complex series of coordinated events involving interaction between the male and female gametophyte. We report here molecular data on one of the key events underpinning this process – the death of the receptive synergid cell and the coincident bursting of the pollen tube inside the ovule to release the sperm. We show that two REM transcription factors, VALKYRIE (VAL) and VERDANDI (VDD), both targets of the ovule identity MADS-box complex SEEDSTICK-SEPALLATA3, interact to control the death of the receptive synergid cell. In vdd-1/+ mutants and VAL_RNAi lines, we find that GAMETOPHYTIC FACTOR 2 (GFA2), which is required for synergid degeneration, is downregulated, whereas expression of FERONIA (FER) and MYB98, which are necessary for pollen tube attraction and perception, remain unaffected. We also demonstrate that the vdd-1/+ phenotype can be rescued by expressing VDD or GFA2 in the synergid cells. Taken together, our findings reveal that the death of the receptive synergid cell is essential for maintenance of the following generations, and that a complex comprising VDD and VAL regulates this event.
Author contributions
M.A.M. designed and performed most of the experiments and wrote the manuscript. R.F.G. designed and employed the RNA interference construct and performed the ChIP experiment. B.C. performed statistical analyses. Y.S.V. performed TEM imaging. P.M. performed the Pearson coefficient analysis. S.M. made the complementation constructs. N.B. and R.G.H. executed the pCKX7::GUS marker line. H.D. designed the TEM experiment and contributed to writing the manuscript. L.C. designed the experiments and wrote the manuscript.
Funding
M.A.M. was supported by fellowships from the Portuguese National Funding Agency for Science, Research and Technology (Fundação para a Ciência e a Tecnologia) [SFRH/BPD/99936/2014], by the European Union Initial Training Network (ITN) SYSFLO 2010-2013, and by a grant from the European Commission, Marie Curie Action ‘Networks for Initial Training’ - SYSFLO - Training in Systems Biology Applied to Flowering [FP7-PEOPLE-ITN-2008]. L.C. was supported by Ministero dell'Istruzione, dell'Università e della Ricerca MIUR-PRIN 2012.
Data availability
Correlation analysis data for STK and VDD are available on Figshare at: https://dx.doi.org/10.6084/m9.figshare.3464054.v2 (Table S1) and https://dx.doi.org/10.6084/m9.figshare.3464057.v2 (Table S2).
