A key decision for plants is when to flower; this is influenced by day length. In Arabidopsis, a facultative long-day plant, the florigen FLOWERING LOCUS T (FT) and its paralog TWIN SISTER OF FT (TSF) are key regulators, produced in the phloem and transported to the shoot apical meristem (SAM) in which they activate expression of downstream targets to induce the flowering programme. FT binds to the lipid phosphatidylcholine (PC), and its activity is regulated by PC levels, and hence by the activity of the enzyme PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE 1 (PECT1). Consistent with this, downregulation of PECT1 leads to an acceleration in flowering time. However, it has also been shown that this phenotype is at least partially independent of FT and TSF, raising the question as to how else PECT1 might influence flowering time. Now, Ji Hoon Ahn and colleagues show that downregulation of PECT1 in the SAM leads to impaired expression of the transcription factor SHORT VEGETATIVE PHASE (SVP). It is known that SVP inhibits gibberellin synthesis, and that – under short-day conditions – gibberellin promotes flowering. The authors provide evidence that the early flowering phenotype seen upon PECT1 knockdown can be partially rescued by overexpression of SVP or by a gibberellin inhibitor. Although it is still unclear how PECT1 regulates SVP, these data uncover a new florigen-independent mechanism influencing flowering time.
