Significance Proper timing of flowering transition is vital for the reproductive success of plants and orchestrated by endogenous and external factors; however, the mechanisms of how plants regulate flowering under high light are not well understood. In this study, we show that promotion of flowering by high light involves the coupling of chloroplast retrograde signals and transcriptional silencing of the floral repressor FLOWERING LOCUS C ( FLC ). In response to high light, a chloroplast envelope-localized transcription factor, PTM, releases its N-terminal fragment through processing to associate with the chromatin remodeler FVE and suppresses FLC transcription. This report describes the molecular basis for a unique intracellular signaling pathway derived from chloroplasts in which plants regulate the developmental timing of the flowering transition.
