Cell-to-cell translocation of florigen is inhibited by low ambient temperature through abscisic acid signaling in Arabidopsis thaliana

Sep 29, 2026

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Florigen, encoded by the FLOWERING LOCUS T (FT) gene, is produced in leaf phloem companion cells and acts in the shoot apical meristem (SAM) to trigger flowering. The study addresses how FT cell-to-cell transport within the SAM is regulated under environmental conditions. Using an in vivo bimolecular fluorescence complementation assay, the authors show that low ambient temperature suppresses FT intercellular translocation via abscisic acid (ABA) signaling and by inducing callose synthase genes that reduce plasmodesmatal permeability, delaying flowering.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Significance

Molecular basis of FT transport under low temperature

ABA signaling and plasmodesmata permeability

Implications for florigen activity and flowering

RESEARCH ARTICLE PLANT BIOLOGY Cell-to-cell translocation of florigen is inhibited by low ambient temperature through abscisic acid signaling in Arabidopsis thaliana Yusuke Murataa, Kenji Nagataa , and Mitsutomo Abea,1 Edited by Richard Amasino, University of Wisconsin-Madison, Madison, WI; received April 18, 2025; accepted June 3, 2025 In Arabidopsis thaliana, the FLOWERING LOCUS T (FT) gene encodes florigen, a floral stimulus that integrates multiple environmental cues to optimize the timing of flowering, which is crucial for reproductive success. The FT protein is synthesized in the phloem companion cells of leaves but exerts its function in the shoot apical meristem (SAM) to initiate floral morphogenesis. While the environment-dependent regulation ofFT transcription in leaves is well studied, the mechanisms underlying FT transport, particularly its cell-to-cell translocation within the SAM, remain poorly understood. In this study, we employed an in vivo bimolecular fluorescence complementation assay to elucidate the molecular mechanisms regulating FT intercellular translocation in the SAM. We demonstrate that low ambient temperature inhibits the cell-to-cell movement of FT in the SAM through abscisic acid signaling pathways, resulting in flowering delay. We further show that the permeability of plasmodesmata (PD) is involved in FT transport; in particular, CALLOSE SYNTHASE ( CalS) 1 and CalS7 are induced at low temperature, leading to reduced permeability of PD and inhibition of symplastic FT translocation in the SAM. Collectively, our findings provide insights into the molecular mechanisms that regulate the intercellular translocation ofFT in the SAM in response to environmental conditions and lead to a framework for the understanding of flowering. florigen | flowering | shoot apical meristem | plasmodesmata | symplastic translocation Maximizing reproductive success is fundamental to all organisms. In annual plants, optimal flowering time is essential for reproductive success. Onset of flowering is regulated by multiple genetic pathways that are triggered by various exogenous and endogenous environmental cues, such as photoperiod, ambient temperature, and phytohormones (1–4), and that ultimately results in the expression of florigen, a floral stimulus, in phloem companion cells (CCs) of leaves (1–4) . In Arabidopsis thaliana, the FLOWERING LOCUS T (FT) protein is an essential component of florigen (5–12) . Under flowering-inducing conditions, FT mRNA is expressed in the phloem CCs of leaves in response to environmental cues. The resulting FT protein is then transported from the leaves to the shoot apical meristem (SAM), where it interacts with the bZIP transcription factor FD to regulate the expression of floral meristem identity genes (e.g., APETALA1) (7–10, 12, 13) . Consequently, to comprehend the molecular mechanisms by which FT determines the timing of flowering, it is essential to consider not only the expression ofFTin leaves but also the transport ofFT from leaves to the SAM. A previous study has shown that transport ofFT from the leaves to the SAM is divided into four distinct steps (14). First, FT is loaded from phloem CCs in the leaves into sieve elements (SEs). Second, FT enters the phloem stream and moves toward the SAM. Third, FT is unloaded from the end of the phloem tissue into cells beneath the SAM. Fourth, FT is translocated intercellularly to the corpus cells in the SAM, where FD is predominantly expressed. In Arabidopsis, the first step of loading FT into SEs is modulated by FT INTERACTING PROTEIN 1 (FTIP1), a C2 domain-containing endoplasmic reticulum protein (15), the FTIP1 homolog QUIRKY (16), and SYNTAXIN OF PLANTS 121, a member of the soluble N-ethylmaleimide-sensitive factor protein attachment protein receptor superfamily (16) . Temperature-dependent changes in membrane lipid composition also affect the export ofFT from CCs to SEs in leaves (17). The second step, long-distance

FAQs

What problem does the paper focus on regarding florigen (FT)?

It investigates how FT is transported cell-to-cell within the shoot apical meristem and why this transport becomes inefficient under low ambient temperature.

How does low ambient temperature affect FT movement in the SAM?

Low ambient temperature inhibits FT cell-to-cell translocation in the SAM, leading to delayed flowering.

What role does abscisic acid (ABA) signaling play in the mechanism?

ABA signaling induces CALLOSE SYNTHASE genes, increases callose accumulation, reduces plasmodesmata permeability, and restricts symplastic FT translocation.

Sep 29, 2026

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