TERMINAL FLOWER 1-FD complex target genes and competition with FLOWERING LOCUS T

Abstract

Plants monitor seasonal cues to optimize reproductive success by tuning onset of reproduction and inflorescence architecture. TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT) and their orthologs antagonistically regulate these life history traits, yet their mechanism of action, antagonism and targets remain poorly understood. Here, we show that TFL1 is recruited to thousands of loci by the bZIP transcription factor FD. We identify the master regulator of floral fate, LEAFY (LFY) as a target under dual opposite regulation by TFL1 and FT and uncover a pivotal role of FT in promoting flower fate via LFY upregulation. We provide evidence that the antagonism between FT and TFL1 relies on competition for chromatin-bound FD at shared target loci. Direct TFL1-FD regulated target genes identify this complex as a hub for repressing both master regulators of reproductive development and endogenous signalling pathways. Our data provide mechanistic insight into how TFL1-FD sculpt inflorescence architecture, a trait important for reproductive success, plant architecture and yield.

Regulation by FLOWERING LOCUS T and TERMINAL FLOWER 1 in Flowering Time and Plant Architecture

“…[ 17 ] With the assistance of the bZIP transcription factor FD, TFL1 is recruited to the LFY chromatin and regulates LFY expression. [ 120,121 ] Conversely, AP1 and LFY repress TFL1 expression in the FM (Figure 4 and Table 2 ). [ 118,122,123 ] Loss‐of‐function mutants of both LFY and AP1 result in the transformation of flowers into inflorescence‐like shoots, whereas ectopic expression of LFY and AP1 causes early flowering and prematurely terminates inflorescence as a FM, largely because of the reduced expression of TFL1 .…”

Abscisic Acid and Flowering Regulation: Many Targets, Different Places

“…While the organization of these regulatory networks at the shoot apex is currently unclear, further confirmation for this interplay between FD and ABA-related genes derives from ChIP and expression analyses of the shoot-specific TFL1 gene. The TFL1-FD complex directly represses, among others, the ABA biosynthetic gene ABA1 , the bZIPs ABF4 / AREB2 and ABI5 together with the ABI5 regulator AFP2 [ 27 ]. Thus, similar to floral targets, a competition between FT and TFL1 might modulate ABA levels or sensitivity in the shoot meristem cells ( Figure 1 ).…”

“…The function of FT is antagonized by a structurally related protein, TERMINAL FLOWER 1 (TFL1), which is also mobile, albeit its range of movement appears to be limited to the shoot meristem cells [ 25 , 26 ]. TFL1 can interact with FD and is recruited via FD at thousands of genomic positions where it exerts transcriptional repression [ 27 , 28 ]. FT outcompetes TFL1 for FD binding and thus activates transcription of FD targets which include floral meristem identity genes, conferring a floral fate to newly arising lateral primordia, and hormone-related gene functions [ 27 , 29 ].…”

“…TFL1 can interact with FD and is recruited via FD at thousands of genomic positions where it exerts transcriptional repression [ 27 , 28 ]. FT outcompetes TFL1 for FD binding and thus activates transcription of FD targets which include floral meristem identity genes, conferring a floral fate to newly arising lateral primordia, and hormone-related gene functions [ 27 , 29 ].…”

Juvenile Leaves or Adult Leaves: Determinants for Vegetative Phase Change in Flowering Plants

“…Molecular analysis showed that FUL is upregulated in plants overexpressing SPL10 , indicating that FUL may function downstream of SPLs in mediating cauline leaf development [ 92 ]. The bZIP transcription factor FD interacts with both the flowering activator FLOWERING LOCUS T (FT) and the flowering repressor TERMINAL FLOWER1 (TFL1); these two complexes act antagonistically on a common set of targets, such as LFY , AP1 , and other flowering genes to induce flowering [ 93 , 94 , 95 ]. SPL3/SPL4/SPL5 interact with the floral activator FD to stimulate flowering under normal light conditions, and FAR-RED ELONGATED HYPOCOTYL3 and FAR-RED IMPAIRED RESPONSE1 prevent SPL3/SPL4/SPL5 activity in shady conditions to suppress flowering [ 96 , 97 ].…”