How to build a shoot: insights from Physcomitrium patens

The evolution of body plans with multiple cell layers provided structural rigidity and enabled tissue specialisation, which were both essential for the colonisation of land by plants. Building such structure requires apical cell divisions that generate merophytes along all three axes (3D growth), as well as the spatial control of cell fate. The shoot (gametophore) of the moss Physcomitrium patens is an ideal model for studying these processes. Recent studies have identified a genetic network integrating hormone signalling, cell wall biosynthesis and cell shape to regulate division orientation in the gametophore. Additionally, reporter-based markers have revealed localised hormone activity that maintains the gametophore apical cell. This review summarises these findings to provide an updated perspective on 3D growth in Physcomitrium patens.