The exocyst complex contributes to PIN auxin efflux carrier recycling and polar auxin transport in Arabidopsis

Abstract

SUMMARYIn land plants polar auxin transport is one of the substantial processes guiding whole plant polarity and morphogenesis. Directional auxin fluxes are mediated by PIN auxin efflux carriers, polarly localized at the plasma membrane. The polarization of exocytosis in yeast and animals is assisted by the exocyst: an octameric vesicle-tethering complex and an effector of Rab and Rho GTPases. Here we show that rootward polar auxin transport is compromised in roots of Arabidopsis thaliana loss-of-function mutants in the EXO70A1 exocyst subunit. The recycling of PIN1 and PIN2 proteins from brefeldin-A compartments is delayed after the brefeldin-A washout in exo70A1 and sec8 exocyst mutants. Relocalization of PIN1 and PIN2 proteins after prolonged brefeldin-A treatment is largely impaired in these mutants. At the same time, however, plasma membrane localization of GFP:EXO70A1, and the other exocyst subunits studied (GFP:SEC8 and YFP:SEC10), is resistant to brefeldin-A treatment. In root cells of the exo70A1 mutant, a portion of PIN2 is internalized and retained in specific, abnormally enlarged, endomembrane compartments that are distinct from VHA-a1-labelled early endosomes or the trans-Golgi network, but are RAB-A5d positive. We conclude that the exocyst is involved in PIN1 and PIN2 recycling, and thus in polar auxin transport regulation.

Analysis of Exocyst Subunit EXO70 Family Reveals Distinct Membrane Polar Domains in Tobacco Pollen Tubes

“…The small area of NtEXO70A1a localization corresponds to the previously described area of exocytosis maximum in the pollen tube (Bove et al, 2008;Idilli et al, 2013;Luo et al, 2016). This localization is in accordance with previous characterizations of Arabidopsis EXO70A1 as the isoform generally responsible for exocytosis in many plant tissues (Synek et al, 2006;Hála et al, 2008;Samuel et al, 2009;Kulich et al, 2010;Drdová et al, 2013;Fendrych et al, 2013;Zhang et al, 2016;Vukašinovi c et al, 2017). In accordance with the published observations, NtEXO70A1a localizes both to the cytoplasm and to the specific area of the PM.…”

Endosidin2 targets conserved exocyst complex subunit EXO70 to inhibit exocytosis

“…1 I and J), indicating that ES2 treatment reduced PIN2 recycling through endosomes. Similar delayed PIN2 recycling has been observed in mutants that are defective in exocytosis (23).…”

Exploring exocytosis using chemical genomics

“…Intriguingly, although the overall phenotypic effect of long-term ES2 treatment matches that of EXO70A1 knockout mutants, short-term treatments with ES2 reveals novel facets of EXO70 action. Notably, with short-term treatment of ES2, a significantly greater quantity of PIN2 was found to accumulate in the prevacuolar compartments compared with the loss-of-function mutants described earlier (16). This observation brings forth the unique advantage of transient inhibition by chemical effectors, which is often phenotypically more prominent than the equilibrated cellular conditions of genetic knockouts.…”