A groundbreaking study published in Nature in 2025 unravels the intricate molecular choreography underlying the initiation of flowering in Arabidopsis, one of the most extensively studied plant models. Researchers have illuminated the dynamic assembly of the Florigen Activation Complex (FAC), a pivotal molecular unit that orchestrates the transition from vegetative growth to flowering, unlocking new vistas into how plants integrate developmental and environmental signals to precisely time their reproductive phase.
Central to this discovery is the protein FT, known as florigen, which accumulates in distinct cellular populations within floral primordia, the rib zone, and the organizing and central zones of the shoot apical meristem (SAM). These are regions fundamental for meristem maintenance and floral development. Crucially, FT does not act in isolation; it co-localizes with the transcription factor FD and adaptor 14-3-3 proteins, forming a triad that synergistically propels flowering. This cellular colocalization underpins a spatially defined recruitment of FT that was previously unseen using endogenous promoter systems, refining prior observations that employed artificial overexpression methods.
Intriguingly, FT’s expression pattern within the floral primordium unfolds in a temporal sequence starting at the adaxial side and progressing beneath the AP1 expression domain, which demarcates the suppressed bract boundary. This nuanced spatial regulation contributes to floral identity by influencing the formation of fewer cauline leaves and branches, reflecting FT’s genetically established role in inflorescence architecture. While FT cooperates with FD to activate AP1 transcription, the study reveals this interaction likely initiates rather than sustains AP1 expression, emphasizing a stage-specific regulatory mechanism that fine-tunes floral meristem identity.
Another layer of complexity arises from BLADE ON PETIOLE (BOP) proteins, which also define the floral primordium’s boundary and positively regulate AP1 transcription. The precise interplay between BOP proteins and FT remains an open question, highlighting the intricate network of transcriptional regulators sculpting floral transition. Such discoveries hint at a sophisticated regulatory architecture where boundaries and identities within the meristem are maintained by overlapping yet distinct molecular circuits.
The temporal and spatial dynamics distinguishing FT from its antagonistic counterpart, TERMINAL FLOWER 1 (TFL1), were also explored. Contrary to previous models suggesting simple competitive inhibition, the researchers demonstrate that FT and TFL1 display distinct accumulation patterns in the SAM and primordia, with a brief period of mRNA co-expression in the earliest floral primordium. This finding redefines our understanding of the antagonism between these two pivotal proteins, indicating their functions pivot on differential localization and timing rather than solely molecular competition.
Mechanistically, the study uncovers that the FD-14-3-3 complex binds directly to chromatin and serves as a critical platform for FT recruitment. Notably, the intrinsically disordered C-terminal domain of FT interfaces with DNA only when the FD-14-3-3 complex is present, underscoring an evolutionarily conserved molecular interface that drives floral promotion more potently than previously recognized 14-3-3 interaction sites. This dual-interface model substantially advances our grasp of how florigen physically integrates into transcriptional regulatory assemblies.
Beyond structural insights, the work delves into the biophysical realm of biomolecular condensates—phase-separated assemblies increasingly recognized for regulating developmental programs in plants. FD contains intrinsically disordered regions prone to form condensates, especially when mutations disrupt 14-3-3 binding. Such phase separation appears to impair FAC function in vivo, revealing that 14-3-3 proteins act as molecular chaperones to suppress condensate formation, thereby stabilizing FD dimers, enhancing DNA binding affinity, and ultimately facilitating robust transcriptional activation of flowering genes.
This nuanced regulatory mechanism suggests that phosphorylation of FD at threonine 282 serves as a molecular switch: phosphorylated FD predominates during active floral promotion, whereas non-phosphorylated FD may accumulate in condensates under specialized developmental or environmental states, potentially acting as a dormant reservoir. This phosphorylation-dependent toggling offers a dynamic system by which plants can rapidly adjust flowering responses to fluctuating conditions.
Notably, the relevance of these findings extends beyond floral regulators. Group A bZIP transcription factors, to which FD belongs, coordinate diverse developmental transitions and abiotic stress responses, particularly abscisic acid (ABA)-mediated pathways. The study’s insights into 14-3-3 regulation and interface biochemistry shed light on the broader regulatory principles guiding bZIP factor activity and their modulation by post-translational modifications and chaperone interactions.
Phylogenetic analysis buttresses these functional insights by revealing that PEBP family genes, including FT-like and TFL1-like members, emerged distinctly in gymnosperms and are conserved across seed plants. Such evolutionary conservation implicates the multi-interface mode of florigen function and 14-3-3-mediated modulation as fundamental biological innovations shaping the reproductive strategies of angiosperms and their predecessors.
Complementing experimental data, the authors propose a two-step model for florigen function, noted in both Arabidopsis and rice. Initial accumulation of FT at the SAM base triggers a transcriptional cascade activating FT-like genes in the SAM proper, amplifying the florigen signal and ensuring a decisive flowering transition. This mechanistic motif offers a unifying principle underlying florigen’s multifaceted action across species.
In summary, this research unravels the complex molecular architecture and dynamics of the Florigen Activation Complex, underscoring how spatial distribution, protein interactions, and phase behavior converge to regulate the flowering switch. These discoveries open fertile ground for biotechnological applications aimed at manipulating flowering time, improving crop yield, and adapting plants to climate variability by targeting key molecular interfaces and regulatory nodes within the florigen pathway.
Future investigations will be poised to decipher the elusive relationship between BOP proteins and FT, the precise structural rearrangements induced by 14-3-3 binding, and how environmental signals integrate into this regulatory nexus. Additionally, mapping the conditions triggering FD phosphorylation switches and condensate dynamics in planta will unveil deeper insights into the plasticity of flowering control mechanisms.
This landmark study not only enriches our fundamental comprehension of plant developmental biology but also sets the stage for innovative strategies to harness florigen biology in agriculture and horticulture, promising breakthroughs in crop resilience and productivity under shifting environmental paradigms.
Subject of Research: Molecular mechanisms of the Florigen Activation Complex assembly and regulation in Arabidopsis
Article Title: Florigen activation complex forms via multifaceted assembly in Arabidopsis
Article References:
Gao, H., Ding, N., Wu, Y. et al. Florigen activation complex forms via multifaceted assembly in Arabidopsis. Nature (2025). https://doi.org/10.1038/s41586-025-09704-6
Image Credits: AI Generated
