FT14 - Plant Cell Physiol 49(11 16451658(2008...

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Rapid paper Long-Distance, Graft-Transmissible Action of Arabidopsis FLOWERING LOCUS T Protein to Promote Flowering Michitaka Notaguchi 1, 5 , Mitsutomo Abe 2, 5 , Takahiro Kimura 1 , Yasufumi Daimon 2 , Toshinori Kobayashi 2 , Ayako Yamaguchi 2, 4 , Yuki Tomita 2 , Koji Dohi 3 , Masashi Mori 3 and Takashi Araki 2, * 1 Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan 2 Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8501 Japan 3 Research Institute of Agricultural Resources, Ishikawa Prefectural University, Nonoichi-machi, Ishikawa, 921-8836 Japan Day length perceived by a leaf is a major environmental factor that controls the timing of flowering. It has been believed that a mobile, long-distance signal called florigen is produced in the leaf under inductive day length conditions, and is transported to the shoot apex where it triggers floral morphogenesis. Grafting experiments have shown that flori- gen is transmissible from a donor plant that has been subjected to inductive day length to an uninduced recipient plant. However, the nature of florigen has long remained elusive. Arabidopsis FLOWERING LOCUS T ( FT ) is expressed in cotyledons and leaves in response to inductive long days (LDs). FT protein, with a basic region/leucine zipper (bZIP) transcription factor FD, acts in the shoot apex to induce target meristem identity genes such as APETALA1 ( AP1 ) and initiates floral morphogenesis. Recent studies have provided evidence that the FT protein in Arabidopsis and corresponding proteins in other species are an important part of florigen. Our work shows that the FT activity, either from overexpressing or inducible transgenes or from the endogen- ous gene, to promote flowering is transmissible through a graft junction, and that an FT protein with a T7 tag is transported from a donor scion to the apical region of recipient stock plants and becomes detectable within a day or two. The sequence and structure of mRNA are not of critical importance for the long-distance action of the FT gene. These observations led to the conclusion that the FT protein, but not mRNA, is the essential component of florigen. Keywords: Arabidopsis — Flowering — Florigen — FT — Graft — Long-distance signal. Abbreviations: bZIP, basic region/leucine zipper; CBB, Coomassie brilliant blue; CL, continuous light; EGFP, enhanced green fluorescent protein; FT, FLOWERING LOCUS T; GFP, green fluorescent protein; GUS, b -glucuronidase; Hd3a, Heading date 3a; HSP, heat- shock protein; LD, long day; ORF, open reading frame; 35S, cauliflower mosaic virus 35S RNA promoter; SAM, shoot apical meristem; SD, short day; TFL1, TERMINAL FLOWER 1; UTR, untranslated region; ZT, zeitgeber time. Introduction Seasonal flowering is an important adaptive trait in plants that has direct consequences on reproductive success.
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