TERMINAL FLOWER 1 functions as a mobile transcriptional co-factor in the Arabidopsis thaliana shoot apical meristem

The floral transition is a critical step in the plant life cycle and several mechanisms control this finely orchestrated process. TERMINAL FLOWER 1 (TFL1) is a floral repressor and close relative of the florigen, FLOWERING LOCUS T (FT). During floral transition TFL1 expression is up-regulated in the apex to maintain the indeterminate growth of the shoot apical meristem (SAM). Both TFL1 and FT are mobile proteins, but they move in different ways. FT moves from the leaves to the SAM while TFL1 appears to move within the SAM. The importance of TFL1 movement for its function in the regulation of flowering time and shoot indeterminacy and its molecular function are still largely unclear. Our results indicate that the TFL1 protein moves from its place of expression in the centre of the SAM all the way to the meristem layer L1 where it regulates the floral transition. ChIP-seq and RNA-seq demonstrate that TFL1 functions as a co-transcription factor that associates with and regulates the expression of hundreds of genes. Some putative direct targets of TFL1 have been identified, opening the possibility to discover new roles for TFL1 in the regulation of floral transition and inflorescence development.