Table of Contents
Cover image

In many flowering plants, the zygote divides asymmetrically giving rise to a small apical cell and a larger basal cell. The apical cell differentiates into the embryo proper and, ultimately, forms most of the post-germination sporophytic plant. On the other hand, derivatives of the basal cell give rise primarily to the suspensor, a terminally-differentiated region that anchors the embryo to surrounding seed tissue and serves as a conduit for growth factors and nutrients into the embryo proper. Little is known about the mechanisms that cause the apical and basal cells to follow distinct developmental pathways. On pages 2409–2425 of this issue, Weterings et al. utilize the giant embryos of the Scarlet Runner Bean as a model system to identify mRNAs that are specifically localized in the suspensor. The authors show that suspensor-specific mRNAs, designated as C541 and G564, accumulate asymmetrically in embryo basal cells shortly after division of the zygote. Basal cell accumulation of G564 mRNA was shown to be a result of transcriptional regulatory events, and regions of the G564 promoter that play a role in this process were identified. These results demonstrate that following division of the zygote, the apical and basal cells are programmmed transcriptionally to follow independent developmental pathways. The cover shows the selective accumulation of G564 mRNA in the suspensor of a Scarlet Runner Bean embryo.