Polar auxin transport controls suspensor fate.

Polar auxin transport is critical for normal embryo development in angiosperms. It has been proposed that auxin accumulates dynamically at specific positions, which in early Arabidopsis embryos correlates with developmental decisions such as specification of the apical cell lineage, specification of the hypophysis, and differentiation of the two cotyledons. In conifers, pattern formation during embryo development is different, and includes a free nuclear stage, nondividing suspensor cells, presence of tube cells, lack of hypophysis and formation of a crown of cotyledons surrounding the shoot apical meristem. We have recently shown that polar auxin transport is important for normal embryo development also in conifers. Here we suggest a model where auxin is transported from the suspensor cells to the embryonal mass during early embryogeny in conifers. This transport is essential for the developmental decisions of the tube cells and the suspensor, and affects both the amount of programmed cell death and the embryo patterning.