Many environmental factors critical for plant growth and reproduction vary in abundance from season to season. A fundamental means by which plant species cope with this challenge is through monitoring day length, the environmental signal that most reliably predicts calendar date. Based on that information, individuals then either continue vegetative growth or initiate flowering. The most favorable time of year for flowering differs by location. For instance, winter arrives earlier at higher latitudes and elevations. Therefore, understanding how and why photoperiodic flowering responses have been adjusted to permit species to thrive across broad geographic ranges is important knowledge that can inform efforts to preserve biodiversity and successfully manage crops in the face of a changing environment. The proposed work will address this goal by studying how populations of the common monkeyflower, Mimulus guttatus, vary along elevation gradients in the critical day length necessary to induce flowering. The molecular changes and ecological impacts of this variation will be investigated with complementary studies in the lab and field. These combined datasets will then permit development of predictive models to test whether populations will be resilient to future climates. The investigators - working with undergraduates at three University of California institutions, the USA National Phenology Network, and volunteers - will also develop a new citizen science initiative to monitor the flowering of important wildflower species in remote alpine locations along the Pacific Crest Trail.
Although much is known about the molecular mechanisms by which photoperiod regulates flowering in controlled conditions, far less is understood about how these pathways function in natural seasonal conditions or what adjustments to these pathways may prove beneficial in future climates. Preliminary work in M. guttatus has shown that replicate altitudinal shifts in critical photoperiod evolved through changes at distinct sets of loci. The proposed research will characterize the genetic basis and physiological consequences of these diverse mechanisms by utilizing the extensive genomic toolkit available in this emerging model plant system. Specifically, the molecular basis of range-wide variation in critical photoperiod will be established. Through transcriptional analyses under controlled conditions and through field trials, the investigators will also test whether the distinct sets of loci that achieve similar shifts in critical photoperiod do so via equivalent modifications of downstream expression within the flowering gene regulatory network or have unique effects that are adaptive within each local environment. The former finding would suggest a broad capacity for physiological systems to adjust to novel conditions, and the latter would suggest genetic variation may prove a significant constraint on the pace of adaptation. Finally, through investigating forms of diversity abundant in annual M. guttatus but not well explored in other model plants, the proposed research will extend ecophysiological models of flowering time and foster more accurate forecasts of the impact of environmental variation on plant growth and population distribution.
