A Lignin Molecular Brace Controls Precision Processing of Cell Wall Critical for Surface Integrity in Arabidopsis

The cell wall is a defining feature of plant cells and glues cells to each other. To overcome this physical constraint, plants must process and disconnect cell wall linkages during growth and development. However, little is known about the mechanism guiding cell-cell detachment and cell wall remodeling. Here, we identify two neighboring cell types in Arabidopsis that coordinate their activities to control cell wall processing, thereby ensuring precise abscission to discard organs. One cell type produces a honeycomb structure of lignin, which acts as a mechanical 'brace' to localize cell wall breakdown and spatially limit abscising cells. The second cell type undergoes transdifferentiation into epidermal cells, forming protective cuticle, demonstrating de novo specification of epidermal cells, previously thought to be restricted to embryogenesis. Loss of the lignin brace leads to inadequate cuticle formation, resulting in surface barrier defects and susceptible to infection. Altogether, we show how plants precisely accomplish abscission. Overall design: RECs (Residuum cells, abscission zone cells of the receptacle) and SECs (Secession cells, abscission zone cells of separated floral organs) were isolated using fluorescence-activated cell sorting of cells from transgenic plants harboring proQRT2::nlsGFP–GUS construct, and their transcriptomes were analyzed by RNA-sequencing.