Abstract
One key factor defining root system architecture is root branching, i.e., the process of the formation of new root axes, called lateral roots (LRs), from an existing root. In the model plant Arabidopsis thaliana, LRs originate from preselected pericycle cells that divide to create an LR primordium (LRP) that grows and eventually forms a new root apical meristem (Banda et al., 2019). During this developmental process, cell-fate acquisition is very plastic and depends on positional information rather than on cell lineage (Banda et al., 2019). Importantly, LR formation occurs inside the parent root, and the LRP must grow through overlying tissues before emerging into the soil. This LR emergence process is controlled by dynamic intercellular signaling and involves a tight coordination of cellular responses in the LRP and surrounding tissues (Banda et al., 2019). In particular, the growing LRP rapidly pushes against the overlying endodermis, a layer of cells mechanically reinforced by the Casparian strip. The crossing of the endodermis by the LRP between stages IV and V has been proposed as an important developmental checkpoint during LR development (Banda et al., 2019)