Molecular mechanisms of meristem development in fern gametophytes and sporophytes

Seed plants develop specialized structures at their shoot tips called shoot apical meristems, which contain stem cells responsible for upward growth, leaf formation, and eventually, the production of flowers and fruits. Ferns, which are vascular plants but reproduce through spores instead of seeds, also develop shoot meristems; however, these structures differ significantly in their organization and morphology from those in seed plants. Additionally, ferns possess unique meristems crucial to their life cycle that are absent in seed plants, such as leaf meristems that drive prolonged vegetative growth and multicellular meristems during their reproductive gametophyte phase. This project aims to uncover the fundamental processes guiding the formation and maintenance of these diverse meristems in ferns. The research will identify key regulators that are either shared across plant lineages or unique to ferns. The outcomes will enhance the understanding of how plant developmental strategies evolved over time. Besides advancing scientific knowledge, the project will actively engage students and teachers in STEM fields. Each summer, high school science teachers will receive hands-on training through the Purdue professional summer institute workshop, enabling them to develop interacting biology labs using ferns. High school and undergraduate students will be recruited through established institutional programs, directly participating in fern research. Additionally, undergraduate students will benefit by integrating aspects of this project into their plant anatomy coursework, gaining practical experience in sample analysis and microscopic observation. The fern, Ceratopteris richardii, undergoes an alteration of generations between independently growing haploid gametophytes and diploid sporophytes, each containing distinct types of meristems. Using Ceratopteris as a model system, this project will dissect complex signaling networks mediated by key transcriptional regulators during shoot and leaf meristem development in fern sporophytes. Additionally, the project will examine the expression dynamics and functional roles of a highly conserved microRNA family in meristems across both gametophyte and sporophyte phases of the fern lifecycle. To achieve these goals, this project will integrate multiple approaches, leveraging robust Ceratopteris transgenic systems, including CRISPR-mediated genome editing, gene silencing, inducible gene activation, and fluorescence reporters for specific genes, proteins, and cell types. Additional methods will include phylogenetic analysis, confocal live imaging with quantitative image analysis, biochemical assays, histological analysis, RNA in situ hybridization, and transcriptomic profiling. These studies will provide insights into both conserved and lineage-specific regulatory mechanisms underlying meristem formation and stem cell maintenance across land plants. 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.