Resetting and regulation of FLOWERING LOCUS C expression during Arabidopsis reproductive development

Authors

  • Jean Choi,

    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
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    • These authors contributed equally to this work.

  • Youbong Hyun,

    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
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    • These authors contributed equally to this work.

  • Min-Jeong Kang,

    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
    2. Global Research Laboratory for Floral Regulatory Signaling at SNU & UW, Seoul National University, Seoul 151-742, Korea,
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    • These authors contributed equally to this work.

  • Hye In Yun,

    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
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  • Jae-Young Yun,

    1. Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA,
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  • Clare Lister,

    1. Department of Cell and Developmental Biology, John Innes Centre, Norwich, NR4 7UH, UK, and
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  • Caroline Dean,

    1. Department of Cell and Developmental Biology, John Innes Centre, Norwich, NR4 7UH, UK, and
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  • Richard M. Amasino,

    1. Global Research Laboratory for Floral Regulatory Signaling at SNU & UW, Seoul National University, Seoul 151-742, Korea,
    2. Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA,
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  • Bosl Noh,

    Corresponding author
    1. Global Research Laboratory for Floral Regulatory Signaling at SNU & UW, Seoul National University, Seoul 151-742, Korea,
    2. Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju, 660-701, Korea
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  • Yoo-Sun Noh,

    Corresponding author
    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
    2. Global Research Laboratory for Floral Regulatory Signaling at SNU & UW, Seoul National University, Seoul 151-742, Korea,
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  • Yeonhee Choi

    Corresponding author
    1. Department of Biological Sciences, Seoul National University, Seoul, 151-742, Korea,
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(fax +82 2 871 6673; e-mail yhc@snu.ac.kr, ysnoh@snu.ac.kr, or bnoh2003@yahoo.co.kr).

Summary

The epigenetic regulation of the floral repressor FLOWERING LOCUS C (FLC) is one of the critical factors that determine flowering time in Arabidopsis thaliana. Although many FLC regulators, and their effects on FLC chromatin, have been extensively studied, the epigenetic resetting of FLC has not yet been thoroughly characterized. Here, we investigate the FLC expression during gametogenesis and embryogenesis using FLC::GUS transgenic plants and RNA analysis. Regardless of the epigenetic state in adult plants, FLC expression disappeared in gametophytes. Subsequently, FLC expression was reactivated after fertilization in embryos, but not in the endosperm. Both parental alleles contributed equally to the expression of FLC in embryos. Surprisingly, the reactivation of FLC in early embryos was independent of FRIGIDA (FRI) and SUPPRESSOR OF FRIGIDA 4 (SUF4) activities. Instead, FRI, SUF4 and autonomous-pathway genes determined the level of FLC expression only in late embryogenesis. Many FLC regulators exhibited expression patterns similar to that of FLC, indicating potential roles in FLC reprogramming. An FVE mutation caused ectopic expression of FLC in the endosperm. A mutation in PHOTOPERIOD-INDEPENDENT EARLY FLOWERING 1 caused defects in FLC reactivation in early embryogenesis, and maintenance of full FLC expression in late embryogenesis. We also show that the polycomb group complex components, Fertilization-Independent endosperm and MEDEA, which mediate epigenetic regulation in seeds, are not relevant for FLC reprogramming. Based on our results, we propose that FLC reprogramming is composed of three phases: (i) repression in gametogenesis, (ii) reactivation in early embryogenesis and (iii) maintenance in late embryogenesis.

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