Cell-cycle status of male and female gametes during Arabidopsis reproduction

Fertilization in Arabidopsis thaliana is a highly coordinated process that begins with a pollen tube delivering the two sperm cells into the embryo sac. Each sperm cell can then fertilize either the egg or the central cell to initiate embryo or endosperm development, respectively. The success of this double fertilization process requires a tight cell cycle synchrony between the male and female gametes to allow karyogamy (nuclei fusion). However, the cell cycle status of the male and female gametes during fertilization still remains elusive as DNA quantification and DNA replication assays have given conflicting results 1–4 . Here, to reconcile these results, we quantified the DNA replication state by DNA sequencing and performed microscopic analyses of fluorescent markers covering all the phases of the cell cycle. We show that male and female gametes in Arabidopsis are both arrested prior to DNA replication at maturity and initiate their DNA replication only during fertilization.