The Specification of Geometric Edges by a Plant Rab GTPase Is an Essential Cell-Patterning Principle During Organogenesis in Arabidopsis
Organogenesis requires plant cells to adjust their shape through coordinated anisotropic growth of shared walls on individual polyhedral faces. Kirchhelle et. al. now show that the geometric edges of cells represent an additional and important spatial domain, specified by a plant Rab GTPase activity that is essential for morphogenesis.
- Plant cells possess a discrete class of vesicles that marks their geometric edges
- These vesicles are defined by a Rab GTPase variant that is unique to plants
- Inhibiting the activity of this GTPase disrupts growth anisotropy and morphogenesis
- Edge-directed traffic is a crucial patterning principle, augmenting facial polarity
Plant organogenesis requires control over division planes and anisotropic cell wall growth, which each require spatial patterning of cells. Polyhedral plant cells can display complex patterning in which individual faces are established as biochemically distinct domains by endomembrane trafficking. We now show that, during organogenesis, the Arabidopsis endomembrane system specifies an important additional cellular spatial domain: the geometric edges. Previously unidentified membrane vesicles lying immediately beneath the plasma membrane at cell edges were revealed through localization of RAB-A5c, a plant GTPase of the Rab family of membrane-trafficking regulators. Specific inhibition of RAB-A5c activity grossly perturbed cell geometry in developing lateral organs by interfering independently with growth anisotropy and cytokinesis without disrupting default membrane trafficking. The initial loss of normal cell geometry can be explained by a failure to maintain wall stiffness specifically at geometric edges. RAB-A5c thus meets a requirement to specify this cellular spatial domain during organogenesis.
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