MYB74 transcription factor guides de novo specification of epidermal cells in the abscission zone of Arabidopsis

Abscission is a pivotal process by which plants shed leaves, fruits, and flowers. This process occurs in the abscission zone comprised of residuum cells (RECs) and secession cells. After abscission, RECs are exposed to the environment and accumulate a protective cuticle layer. While cuticle production is a defining feature of epidermal cells, this cell type is specified during embryogenesis, implying that de novo specification of epidermal cells is occurring during abscission. Here, we reveal at single-cell resolution that nonepidermal RECs transdifferentiate into epidermal cells through three distinct stages. Stress genes are expressed prior to epidermis formation, perhaps protecting the plant during a vulnerable process involving environmental exposure. We find that MYB74 plays a central role in the de novo specification of epidermal cells in the receptacle, a vital link between the pedicel and the silique, which provides water and nutrient transport to the silique. In addition, de novo epidermis formation is favored over wound healing processes, likely because the latter would limit sustained receptacle growth and thus fruit formation. Our work reveals a developmental program by which plants use a transdifferentiation pathway to protect the plant while promoting growth.