Regulation of Temperature-Responsive Flowering by MADS-Box Transcription Factor Repressors

Chilly Repression Stalls Flowering In a cool spring, flowering might be delayed compared to a warm spring, even though the change in day length marches on regardless of temperature. Lee et al. (p. 628 , published online 12 September; see the Perspective by Nilsson ) now show that this delay in flowering is a regulated process, not simply a consequence of sluggish metabolism. In the model plant Arabidopsis , transcription of the gene encoding the regulator SHORT VEGETATIVE PHASE (SVP) is unaffected by temperature, but the stability of the SVP protein is decreased at higher temperatures. Its regulatory partner, FLOWERING LOCUS M ( FLM )- β , is the product of alternative splicing of transcripts from the gene encoding FLM that favors the β form at lower temperatures. SVP and FLM-β form a complex that represses flowering. At lower temperatures, more of the repressive complex is present and flowering is delayed. At higher temperatures, SVP tends to degrade and FLM-β tends not to be produced, yielding reduced levels of the repressive complex, which allows flowering to proceed.