Florigen (II): It is a mobile protein

The true identity of florigen - the molecule(s) that migrates from leaves to apical meristem to initiate flowering - was notoriously elusive, having made it almost the Bigfoot of plant biology. There was never a lack of drama in the field of florigen study, and florigen researchers have once again experienced such a swing in the last two years. We wrote a minireview last year in this journal (Yu et al. 2006) to excitedly salute, among other discoveries, the notion that the flowering locus T (FT) mRNA might be the molecular form of a florigen. However, this hypothesis was challenged in a little less than two years after its initial proposition, and the original paper proposed that the FT mRNA hypothesis was retracted (Huang et al. 2005 Bohlenius et al. 2007). Interestingly enough, the FT gene previously proposed to encode a florigen was never challenged. Rather, the FT protein, instead of the FT mRNA, is now believed to migrate from leaves to the apical meristem to promote floral initiation. In this update, we will share with our readers some entertaining stories concerning the recent studies of florigen in five different plant species. In addition to the published reports referenced in this update, readers may also refer to our previous minireview and references therein for additional background information (Yu et al. 2006).