Live and let die: a REM complex promotes fertilization through synergid cell death in Arabidopsis.

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.