Florigen-producing cells express FPF1-LIKE PROTEIN 1 that accelerates flowering and stem growth in long days with sunlight red/far-red ratio in .

Seasonal changes in spring induce flowering by expressing the florigen, FLOWERING LOCUS T (FT), in . is expressed in unique phloem companion cells with unknown characteristics. The question of which genes are co-expressed with and whether they have roles in flowering remains elusive. Through tissue-specific translatome analysis, we discovered that under long-day conditions with the natural sunlight red/far-red ratio, the -producing cells express a gene encoding FPF1-LIKE PROTEIN 1 (FLP1). The master regulator, CONSTANS (CO), controls expression, suggesting 's involvement in the photoperiod pathway. FLP1 promotes early flowering independently of , is active in the shoot apical meristem, and induces the expression of (), a key E-class homeotic gene. Unlike FT, FLP1 facilitates inflorescence stem elongation. Our cumulative evidence indicates that FLP1 may act as a mobile signal. Thus, FLP1 orchestrates floral initiation together with FT and promotes inflorescence stem elongation during reproductive transitions.