The Right Time and Place for Making Flowers

摘要

Reproductive success in plants depends on the synchronization of flowering within a given species. Many plants have developed a highly complex signaling network that monitors environmental conditions, such as day length, temperature, or nutrient availability, and determines the appropriate timing for flowering (7,2). This is the case for the model plant Arabidopsis thaliana and the pea that both flower in spring when day length and ambient temperature increase, or certain lice varieties and soybeanthat flower early in the fall when days get shorter. The initiation of flowering requires an additional developmental program to specify the floral identity of the new structures that continuously arise at the shoot apex (5). For instance, during the long vegetative phase in Arabidopsis, every primordium, the groups of cells poised to differentiate, forms a leaf. However, once the decision to flower has been made, all newly emerging primordia follow a developmental program that culminates in the formation of flowers rather than leaves. Thus, constructing a flower requites both temporal and spatial information that restricts the initiation of flowering to specific locations. But how this information is integrated has not been clear, Three studies now reveal the molecular mechanism by which this integration is achieved In this issue, Abe et al. on page 1052 (4) and Wigge et al. on page 1056 (.5) report that interaction between Flowering Locus T (FT), a protein encoded by a gene that is expressed in leaves, and FD, a bZIP transcription factor that is present only in the shoot apex, triggers the expression of floral identity genes in the new primordia. The third papei by Huang et al, in this week's Science Express (6) reports how the two factors meet—FT transcript travels from leaf to shoot via the plant vascular tissue.