J Integr Plant Biol. ›› 2024, Vol. 66 ›› Issue (1): 103-120.DOI: 10.1111/jipb.13595

• Cell and Developmental Biology • Previous Articles     Next Articles

Low temperature-mediated repression and far-red light-mediated induction determine morning FLOWERING LOCUS T expression levels

Hayeon Kim1†, Hye Won Kang1†, Dae Yeon Hwang2, Nayoung Lee3, Akane Kubota4, Takato Imaizumi5 and Young Hun Song1,3,6*   

  1. 1. Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea;
    2. Department of Biology, Ajou University, Suwon 16499, Korea;
    3. Plant Genomics and Breeding Institute, Seoul National University, Seoul 08826, Korea;
    4. Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Nara 630‐0192, Japan;
    5. Department of Biology, University of Washington, Seattle, WA 98195, USA;
    6. Institute of Agricultural Life Sciences, Seoul National University, Seoul 08826, Korea
    These authors contributed equally to this work.
    *Correspondence: Young Hun Song (younghsong@snu.ac.kr)
  • Received:2023-09-01 Accepted:2023-12-12 Online:2023-12-13 Published:2024-01-01

Abstract: In order to flower in the appropriate season, plants monitor light and temperature changes and alter downstream pathways that regulate florigen genes such as Arabidopsis (Arabidopsis thaliana) FLOWERING LOCUS T (FT). In Arabidopsis, FT messenger RNA levels peak in the morning and evening under natural long-day conditions (LDs). However, the regulatory mechanisms governing morning FT induction remain poorly understood. The morning FT peak is absent in typical laboratory LDs characterized by high red:far-red light (R:FR) ratios and constant temperatures. Here, we demonstrate that ZEITLUPE (ZTL) interacts with the FT repressors TARGET OF EATs (TOEs), thereby repressing morning FT expression in natural environments. Under LDs with simulated sunlight (R:FR = 1.0) and daily temperature cycles, which are natural LD-mimicking environmental conditions, FT transcript levels in the ztl mutant were high specifically in the morning, a pattern that was mirrored in the toe1 toe2 double mutant. Low night-to-morning temperatures increased the inhibitory effect of ZTL on morning FT expression by increasing ZTL protein levels early in the morning. Far-red light counteracted ZTL activity by decreasing its abundance (possibly via phytochrome A (phyA)) while increasing GIGANTEA (GI) levels and negatively affecting the formation of the ZTL–GI complex in the morning. Therefore, the phyA-mediated high-irradiance response and GI play pivotal roles in morning FT induction. Our findings suggest that the delicate balance between low temperature-mediated ZTL activity and the far-red light-mediated functions of phyA and GI offers plants flexibility in fine-tuning their flowering time by controlling FT expression in the morning.

Key words: far-red light, FLOWERING LOCUS T, flowering time, GIGANTEA, low night-to-morning temperature, natural long days, phytochrome A, red to far-red ratio, ZEITLUPE

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