Discovering mechanisms of short day vegetative growth in plants

Plants use the length of the day, or photoperiod, to anticipate the changing seasons and adjust their growth and flowering accordingly. While decades of research have revealed how plants time flowering to the seasons, far less is known about how photoperiod controls vegetative growth, the production of leaves and biomass that occurs before flowering. Nearly all of what is known about photoperiodic growth comes from species that grow faster during long summer days, leaving a major gap in understanding of plants that grow faster during short winter-like days. Ribwort plantain (Plantago lanceolata) is a common and widely distributed weed with a documented short-day growth habit. This project will establish P. lanceolata as a model system for understanding how plants achieve faster growth in short days. By characterizing the cellular, physiological, and genetic mechanisms that allow this plant to grow faster in short days, the project will reveal whether short-day growth relies on the same biological systems that control long-day growth in other plants, or whether distinct strategies have evolved to achieve these different seasonal outcomes. This knowledge has broad relevance for understanding how plants of all kinds align growth with the seasons and how growing seasons might be extended for agricultural crops as climate patterns shift. Therefore, the research results may lead to improvements in food production and enhancement of other industries that depend upon plant vegetative growth for various products. The project will train graduate students, postdoctoral researchers, and undergraduates in morphological, physiological, and biotechnological approaches, thus contributing to workforce training in these areas. In addition, the award supports ongoing science outreach programs serving New Haven-area schools and the broader public. The project addresses how photoperiod controls vegetative growth in P. lanceolata, a species demonstrated to grow faster during short days, through three integrated aims. The first aim will characterize the cellular basis of enhanced short-day leaf growth, using three-dimensional morphological analysis, regional growth tracking, and assays of cell division and cell expansion to determine which cellular processes drive increased leaf area and mass under short photoperiods. The second aim will determine whether photoperiod regulates photosynthetic performance and photosynthate partitioning between storage and growth-promoting sugars, testing whether P. lanceolata uses a metabolic daylength-sensing strategy analogous to that of long-day growing species. The third aim will generate foundational genomic resources for P. lanceolata, including a high-quality reference genome and transcriptomic and proteomic datasets, which will be made available to the research community. Furthermore, CRISPR-Cas9 mutants of candidate circadian clock and photoperiod-responsive genes will be generated, to identify the molecular mechanisms controlling short-day growth and to test whether they are conserved with or distinct from those of long-day growing plants. Together, these aims will establish essential tools and knowledge for using P. lanceolata as a genetic model system for short-day vegetative growth, filling a critical gap in the study of photoperiodism in plants and providing essential biotechnological resources for future studies. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.