J Integr Plant Biol

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  • 收稿日期:2025-03-15 接受日期:2025-07-15

The bZIP3-AS1 complex promotes CONSTANS-induced FLOWERING LOCUS T activation in a daylength-dependent manner

Wonbok Lee1†, Sun Ho Kim2†, Junsang Park1†, So Hee Yoon1, Sung Won Cho3, Nayoung Lee4, Shogo Ito5,6, Takato Imaizumi6, Jong Chan Hong2, Woo Sik Chung2* and Young Hun Song1,3,4*   

  1. 1. Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea
    2. Division of Applied Life Science (BK21 Four program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 52828, Korea
    3. Research Institute of Agricultural Life Sciences, Seoul National University, Seoul 08826, Korea
    4. Plant Genomics and Breeding Institute, Seoul National University, Seoul 08826, Korea
    5. Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606‐8501, Japan
    6. Department of Biology, University of Washington, Seattle, Washington 98195‐1800, USA

    †These authors contributed equally to this work.
    *Correspondences: Woo Sik Chung (chungws@gnu.ac.kr); Young Hun Song (younghsong@snu.ac.kr, Dr. Song is fully responsible for the distribution of all materials associated with this article)
  • Received:2025-03-15 Accepted:2025-07-15
  • Supported by:
    This work was supported partly by the grant from the National Institutes of Health Grant (No. R01GM079712 to T.I.) and the Basic Science Research Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Education (Nos. RS‐2020‐NR04950 and 2020R1A6A1A03044344 to W.S.C.), and supported by the National Research Foundation (NRF) of Korea grant funded by the Korean government (MSIT) (No. RS‐2024‐00336624 to J.C.H. and No. 2021R1A4A1032888 and No. RS‐2025‐00562751 to Y.H.S.).

Abstract: Plants monitor daylength to synchronize their flowering time with their surroundings and thus maximize reproductive fitness. In Arabidopsis (Arabidopsis thaliana), CONSTANS (CO) activates the expression of FLOWERING LOCUS T (FT); this activation is a crucial aspect of the daylength-dependent regulation of flowering time. Here, we demonstrate that the basic leucine zipper 3 (bZIP3) transcription factor is important for CO-induced FT expression under long photoperiod conditions in Arabidopsis. We isolated bZIP3 as a CO-interacting protein by yeast two-hybrid screening and verified bZIP3–CO complex formation in Arabidopsis through co-immunoprecipitation assays. The temporal and spatial expression patterns of bZIP3 are very similar to those of CO, and bZIP3 protein levels fluctuate throughout the day, with high abundance in the late afternoon. The bzip3 mutant displayed delayed flowering under long photoperiods, whereas bZIP3 overexpression accelerated flowering regardless of daylength. bZIP3 directly binds to the FT promoter region containing CO-responsive elements in vivo. FT messenger RNA (mRNA) levels in the bzip3 mutant and bZIP3 overexpression lines correlated with their flowering times and changed only during the daytime. bZIP3 overexpression resulted in significantly lower FT transcript levels in the co mutant background than in the wild type. Furthermore, bZIP3 forms a complex with ASYMMETRIC LEAVES1 (AS1), a CO partner that helps CO induce FT expression. The bzip3 as1 double mutant flowered later than the two single mutants under longer daylengths, and FT mRNA levels were much lower in the double mutant than in the bzip3 single mutant. Collectively, our findings uncover a new layer of photoperiod-dependent FT regulation in which bZIP3 facilitates CO to activate FT transcription by forming a complex with AS1.

Key words: ASYMMETRIC LEAVES1, bZIP3, CONSTANS, FLOW-ERING LOCUS T, flowering time, photoperiod

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