Understanding Fate Transitions in the Stomatal Lineage of Arabidopsis thaliana

• Main Author: Simmons, Abigail R
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2018
• Subjects: Cellular biology; Developmental biology
• ISBN: 9798662555037

Development, the process by which a single cell gives rise to an entire organism, requires that organisms balance cell proliferation with cell differentiation. While similar themes are found in plant and animal development, multicellularity evolved after the split of the animal and plant lineages 1.6 billion years ago. Thus, few of the actual proteins or pathways are conserved between animals and plants. Plants are known for their developmental flexibility, changing the size and compositions of organs such as leaves in response to the environment. Whole and partial genome duplications in plants have allowed for the expansion of many gene families, leading to subfunctionalization. The increase in the number of cyclins, for example, has led to speculation that different cyclins allow for integration of developmental and environmental information into the cell cycle. Stomata are pores on the surface of the plant epidermis flanked by two guard cells, which allow plants to balance gas exchange with moisture loss and are thus essential for life on land. In addition to the physiological importance of stomata, the stomatal lineage of Arabidopsis thaliana is a microcosm of development. The major regulators of stomatal development are three bHLH transcription factors SPCH, MUTE and FAMA. In stomatal development, first a subset of epidermal precursor cells begins to express SPCH and divide asymmetrically to form stem-cell-like meristemoids, then these meristemoids continue to divide asymmetrically to produce the majority of cells in the leaf epidermis. Next the meristemoid stops expressing SPCH, begins expressing MUTE and transitions into a guard mother cell (GMC). GMCs express FAMA before dividing once, symmetrically, to produce the two guard cells of the stoma. Major cell fate transitions, from meristemoid to GMC and GMC to guard cells, occur and are coordinated with cell divisions. During this process, cell-cell signaling is key for proper patterning of the epidermis, and the lineage responds to signals from the environment and from other tissues. Thus, the stomatal lineage can be used to study many different aspects of development in a tissue that is accessible and amenable to live imaging. While my research in this thesis is focused on Arabidopsis it is worth noting that stomata are found in all higher plants, and my research may be relevant to other plant model species, as well as crop species. In this dissertation, Chapter 1 is an introduction to the literature and is followed by three data chapters (2-4) and a final fifth chapter providing an overall perspective on my work and potential future directions.