Protodermal Stem Cells in the Brachypodium Leaf

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Protodermal stem cells are meristematic cells in the epidermal L1 layer at the base of the developing grass leaf. These stem cells have the capacity to produce all epidermal cell types of a grass leaf like the sealing and stabilizing pavement cells, gas-exchanging stomatal complexes, leaf-rolling bulliform cells and the functionally enigmatic but probably herbivore-deterring prickle hair cells and silica cells. Many of these epidermal cell types do not exist in eudicot model systems like Arabidopsis (e.g. bulliform cells, prickle hair cells) or show grass-specific features (e.g. stomata). As the ultimate barrier shielding the “inner” leaf physiology from “outer” abiotic and biotic stressors, the leaf epidermis is absolutely essential to plant survival. Yet, little is known regarding how protodermal stem cells terminate their pluripotent state and commit to distinct developmental trajectories to make the manifold cell types of the grass leaf epidermis. Here, I propose to use the model grass Brachypodium distachyon—a wild grass that can be used as a model system for Pooid grasses like wheat and barley—to decipher how and where protodermal stem cells lose pluripotency and branch into distinct developmental trajectories. To this end, we will use single-cell transcriptomics, developmental genetics and microscopy. We will leverage my lab’s extensive collection of Brachypodium resources and our immediate access to a mutant Brachypodium collection, which is fully resequenced with all mutations exactly mapped to genomic locations (NaN population). Together, this project will produce an unprecedented resolution of protodermal stem cell trajectories in Brachypodium, test the role of key transcription factor families regulating epidermal lineage trajectory commitment and spatially map where exactly lineage commitment occurs in the meristematic zone of the grass leaf.