PIF transcription factors link a neighbor threat cue to accelerated reproduction in Arabidopsis

Changes in light quality indicative of competition for this essential resource influence plant growth and developmental transitions. Little is known about neighbor proximity-induced acceleration of reproduction. phytochrome B (phyB) senses light cues from plant competitors ultimately leading to the expression of the floral inducers FLOWERING LOCUS ( FT ) and TWIN SISTER of FT ( TSF ). Here we show that three PHYTOCHROME INTERACTING FACTOR (PIF) transcriptional regulators act directly downstream of phyB to promote expression of FT and TSF . Neighbor proximity enhances PIF accumulation towards the end of the day coinciding with enhanced floral inducer expression. We present evidence for direct PIF-mediated TSF expression. The relevance of our findings is illustrated by the prior identification of FT , TSF and PIF4 as loci underlying flowering time regulation in nature. One Sentence Summary PIF transcription factors mediate reproductive transition in response to neighbor proximity light cues in Arabidopsis.