Regulation of the transition from active growth to dormancy in white spruce trees

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The ability of north-temperate forest tree species to synchronize their annual growth cycle to local environmental conditions is critical for long term persistence of the species. Timing of bud formation and transition to dormancy are adaptive traits that represent a trade-off between acquisition of winter hardiness and duration of active growth, which is a determinant of productivity. Because autumnal phenology transitions can only be studied in perennial plants, we know surprisingly little about molecular events that underpin processes such as bud formation, growth cessation, cold acclimation and dormancy acquisition. ***The long term goals of my research are to delineate molecular events that occur during the transition from active growth to dormancy in an economically and environmentally important conifer, white spruce, and to understand how these processes are regulated by daylength and temperature. A mechanistic understanding of autumnal phenology transitions in white spruce can inform tree improvement and conservation programs, particularly in the face of predicted climate change scenarios. I propose four objectives that build upon recent research progress. (1) Determine how day length and temperature regulate autumnal phenology transitions. We will test the hypotheses that specific day lengths and temperatures govern bud development, growth cessation, reserve accumulation, cold acclimation and dormancy acquisition in buds, stems and roots. (2) Identify dormancy biomarkers. Currently, the only method to determine whether a tree is dormant is to assess regrowth under favorable conditions. To overcome this limitation, we will discover genes whose expression patterns correlate with dormancy status. (3) Discover regulators of autumnal phenology transitions through gene functional characterization. We used genomics to identify candidate regulators of white spruce bud development, and we showed that white spruce transcription factors similar to Arabidopsis flowering regulators may regulate bud formation in white spruce. We propose to characterize other candidate regulators that we hypothesize regulate bud formation and dormancy acquisition. (4) Construct transcriptional networks regulating autumnal phenology transitions. We will use transcription factors that we discover to regulate bud formation or dormancy acquisition to uncover new transcription factors that regulate their expression, building regulatory networks that mediate activity-dormancy transition in white spruce. ***Research outcomes will yield mechanistic insights for events that are invoked during autumnal phenology transition in white spruce at molecular, cellular and whole plant scales. This new knowledge will help move the field from observation of phenology patterns to understanding of phenology processes, informing management practices that aim to enhance resiliency of our forests. ********