Complex sentence: It results from the polar/asymmetric localisation at the plasma membrane of the auxin "efflux" carriers of the PIN family, which are secondary transporters that export auxin out of the cells.
Split into simpler sentences: It results from the polar/asymmetric localisation of the auxin "efflux" carriers of the PIN family at the plasma membrane. These proteins work as secondary active transporters that export auxin out of the cells.