Abstract
The phytohormone and morphogen auxin regulates essentially all aspects of plant development from embryogenesis to fruit formation (e.g. Moubayidin and Ostergaard, 2014; Robert et al., 2018).
Uneven or unidirectional cell-to-cell transport is an important property of auxin's mode of action and, together with local auxin biosynthesis or degradation, result in the formation and maintenance of auxin maxima and minima pivotal for proper patterning and development (e.g. Chen et al., 2014; Brumos et al., 2018).
Canonical "long" PIN-FORMED auxin exporters (PINs) are essential for this function because their polar plasma membrane distribution and their ability to repolarize within a cell make them ideal to directionally transport auxin through simple and complex tissues (Bennett, 2015). The abundance of polarly distributed PINs at the plasma membrane, together with mechanisms regulating PIN activity, determines the absolute amount of auxin being exported from a cell in a given direction (Barbosa et al., 2018).