Planar polarity, tissue polarity and planar morphogenesis in plants

Plant tissues commonly undergo morphogenesis within a single tissue layer or between associated cells of the same tissue type such as vascular cells. Tissue morphogenesis may rely on an underlying tissue polarity marked by coordinated unidirectional asymmetric localisation of molecules to ends of cells. When observed in the plane of the tissue layer this is referred to as planar polarity and planar morphogenesis. However, planar morphogenesis can also involve multidirectional or differential growth of cells relying on cell–cell communication. Here, we review recent progress towards an understanding of hormonal coordination and molecular mechanisms underlying planar and tissue polarity as well as planar morphogenesis. Furthermore, we discuss the role of physical forces in planar morphogenesis and the contribution of tissue polarity to plant organ shape.

► Local auxin biosynthesis and transport direct planar polarity in the root epidermis.
► Discovery of interactions between auxin and ROP signalling in the leaf epidermis.
► A role for mechanical stress in planar morphogenesis in the shoot apical meristem.
► Molecular and mechanistic insights into auxin-transport mediated vascular polarity.
► Computational modelling reveals importance of tissue polarity for organ shape.