In perennial plants, seasonal shifts provide cues that control adaptive growth patterns of the shoot apex. However, where these seasonal cues are sensed and communicated to the shoot apex remains unknown. We demonstrate that systemic signals from leaves play key roles in seasonal control of shoot growth in model tree hybrid aspen. Grafting experiments reveal that the tree ortholog of Arabidopsis flowering time regulator FLOWERING LOCUS T (FT) and the plant hormone gibberellic acid (GA) systemically convey seasonal cues to the shoot apex. GA (unlike FT) also acts locally in shoot apex, downstream of FT in seasonal growth control. At the shoot apex, antagonistic factors-LAP1, a target of FT and the FT antagonist TERMINAL FLOWER 1 (TFL1)-act locally to promote and suppress seasonal growth, respectively. These data reveal seasonal changes perceived in leaves that are communicated to the shoot apex by systemic signals that, in concert with locally acting components, control adaptive growth patterns.

Beijing Advanced Innovation Center for Tree Breeding by Molecular Design Beijing Forestry University Beijing 100083 China

Department of Forest Genetics and Plant Physiology Umeå Plant Science Centre Swedish University of Agricultural Sciences SE 901 87 Umeå Sweden

Department of Forest Genetics and Plant Physiology Umeå Plant Science Centre Swedish University of Agricultural Sciences SE 901 87 Umeå Sweden Department of Plant and Microbial Biology University of Zürich 8008 Zürich Switzerland

Department of Forest Genetics and Plant Physiology Umeå Plant Science Centre Swedish University of Agricultural Sciences SE 901 87 Umeå Sweden School of Forest Resources and Environmental Science Michigan Technological University Houghton MI 49931

Laboratory of Growth Regulators Institute of Experimental Botany The Czech Academy of Sciences Faculty of Science Palacký University CZ 78371 Olomouc Czech Republic

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