Plant organs are formed in succession at the shoot apical meristem. Early in development, the shoot apical meristem gives rise to vegetative structures such as leaves; later on, it forms inflorescence branches and flowers. Here, George Coupland and colleagues investigate the role of TERMINAL FLOWER 1 (TFL1), a transcription repressor, in Arabidopsis shoot development. First, the authors construct a TFL1 reporter to analyse its distribution spatially and temporally. They observe two distinct patterns of TFL1 distributions, correlating with the two roles of TFL1 — preventing early flowering during vegetative development and later maintaining meristem indeterminacy (where flowers are repeatedly formed on the stem axis). Then, the authors perform time-resolved RNA-sequencing of wild-type and tfl1-mutant shoots and find that TFL1 acts on two different clusters of genes. The authors propose that TFL1 has two modes of gene regulation — one that blocks transcription of floral organ identity genes and another that modulates the rate of increase in transcription of floral transition genes. Finally, the authors find that repression of transcription of SEP4, which encodes a transcription factor downstream of TFL1, is important for TFL1 function. Overall, the findings contribute to the understanding of the roles of TFL1 in flowering time and shoot indeterminacy.
