Flavonol-mediated stabilization of efflux complexes regulates polar auxin transport

The transport of auxin controls the rate, direction and localization of plant growth and development. The course of auxin transport is defined by the polar subcellular localization of the PIN proteins, a family of auxin efflux transporters. Using blue native PAGE and quantitative mass spectrometry, we identify native PIN core transport units as homo- and heteromers assembled from PIN1, 2, 3, 4 and 7 subunits only. To identify the protein composition of the larger, low stringency-solubilized PIN assembly we affinity-purified GFP-fused PIN proteins from Arabidopsis roots after expression from their native promoters and after the induction of discrete lateral roots, and analyzed the captured proteins by label-free quantitative mass spectrometry (LC-MS/MS).