Several environmental cues, including day length, and endogenous developmental signals regulate the transition from leaf production to flower formation in plants. In Arabidopsis, the growth regulator gibberellin promotes this transition most strongly under short day (SD) conditions. Here (p. 2198), George Coupland and colleagues show how gibberellins also promote flowering in response to long days (LDs). The researchers deplete gibberellins in the vascular tissue or the shoot apical meristem by tissue-specific overexpression of GA2ox7, which catabolises gibberellins. Under LD conditions, gibberellins are needed in the vascular tissue to increase production of a systemic signal that is transported from the leaves to the meristem during floral induction. However, in the meristem, instead of activating the expression of the transcription factor SOC1 (which is needed to induce flowering under SD conditions), in response to LDs, gibberellins regulate the expression of SPL transcription factors, which are needed later during floral induction. Thus, the researchers conclude, gibberellins play spatially distinct roles in promoting flowering under long photoperiods.

© 2012.