A hypothetical model of transcriptionally regulated processes and corresponding up-regulated genes involved in terminal differentiation and death of the Norway spruce embryo-suspensor, as suggested by RNA-seq analysis.

<p>Cells in the upper layers of the suspensor (i.e. adjacent to the embryonal mass) begin to expand with simultaneous reorganization of cell wall and enlargement of vacuole. Thereafter cells initiate PCD by expressing transcription factors and stress-responsive genes. The latter might act to suppress rapid cell death and to allow gradual cell dismantling characteristic for vacuolar PCD. At the basal end of the suspensor, hydrolytic enzymes (proteases and nucleases) execute PCD by processing protein and nucleic acid substrates. Note that some gene names correspond to <i>Arabidopsis</i> homologues.