Two modes of gene regulation by TFL1 mediate its dual function in flowering time and shoot determinacy of Arabidopsis

Plant organ primordia develop successively at the shoot apical meristem
(SAM). In Arabidopsis, primordia formed early in development differentiate
into vegetative leaves, whereas those formed later generate inflorescence
branches and flowers. TERMINAL FLOWER 1 (TFL1), a negative regulator of
transcription, acts in the SAM to delay flowering and to maintain
inflorescence meristem indeterminacy. We used confocal microscopy,
time-resolved transcript profiling, and reverse genetics to elucidate this
dual role of TFL1. We find that TFL1 accumulates dynamically in the SAM
reflecting its dual function. Moreover, TFL1 represses two major sets of
genes. One set includes genes that promote flowering and whose expression
increases earlier in tfl1. The other set is spatially misexpressed in tfl1
inflorescence meristems. The misexpression of these two gene sets in tfl1
mutants depends upon FD transcription factor with which TFL1 interacts.
Furthermore, the MADS-box gene SEPALLATA4, which is upregulated in tfl1,
contributes both to the floral transition and shoot determinacy defects of
tfl1 mutants. Thus, we delineate the dual function of TFL1 in shoot
development in terms of its dynamic spatial distribution and different
modes of gene repression.