Nanodomain distribution and function of PIN-FORMED auxin efflux carriers in the plasma membrane of tobacco cells are defined by their interactions with the cell wall

Plant development is under the morphogenic control of auxin. In addition to biosynthesis and metabolism, auxin concentration gradients are maintained by directional intercellular transport via PIN-FORMED (PIN) auxin efflux carriers. Although the structure-function properties of PINs have been described, it is still unclear whether individual members of PIN family could localize differently within the plasma membrane (PM) and whether their nanodomain distribution defines their function. To address this, we used cultured tobacco cells ( Nicotiana tabacum L., cv. BY-2) and revealed by RNA-seq and RT-qPCR the cell stage-specific presence of transcripts of tobacco PIN homologs. We used high-resolution light microscopy and two independent immunoelectron microscopy techniques in cell lines expressing functional GFP-tagged inducible versions of Nt PIN11T, Nt PIN2T and Nt PIN3bT. We show that Nt PINs are distributed within specific PM nanodomains and that removal of the cell wall alters their appearance. By a series of in vivo microscopic observations, we provide evidence that Nt PIN11T is the most homogenously distributed and the least mobile Nt PIN. Pharmacological treatments suggested that the immobilization of Nt PIN11T depends on the actin and microtubular cytoskeleton and the cell wall composition. Using comparative co-immunoprecipitation (co-IP) analysis of isolated membrane fractions for all three Nt PINs we finally identified several novel interaction partners indicating a preferential association of Nt PIN11T with cell wall GPI-anchored arabinogalactan proteins. In conclusion, our results suggest a model in which specific immobilization of PINs through interactions with the cell wall affects their function.