Interdependence of Endomembrane Trafficking and Actin Dynamics during Polarized Growth of Arabidopsis Pollen Tubes

Yan Zhang,Junmin He,David Lee,Sheila Mccormick

doi:10.1104/pp.109.142349

Abstract

During polarized growth of pollen tubes, endomembrane trafficking and actin polymerization are two critical processes that establish membrane/wall homeostasis and maintain growth polarity. Fine-tuned interactions between these two processes are therefore necessary but poorly understood. To better understand such cross talk in the model plant Arabidopsis (Arabidopsis thaliana), we first established optimized concentrations of drugs that interfere with either endomembrane trafficking or the actin cytoskeleton, then examined pollen tube growth using fluorescent protein markers that label transport vesicles, endosomes, or the actin cytoskeleton. Both brefeldin A (BFA) and wortmannin disturbed the motility and structural integrity of ARA7- but not ARA6-labeled endosomes, suggesting heterogeneity of the endosomal populations. Disrupting endomembrane trafficking by BFA or wortmannin perturbed actin polymerization at the apical region but not in the longitudinal actin cables in the shank. The interference of BFA/wortmannin with actin polymerization was progressive rather than rapid, suggesting an indirect effect, possibly due to perturbed endomembrane trafficking of certain membrane-localized signaling proteins. Both the actin depolymerization drug latrunculin B and the actin stabilization drug jasplakinolide rapidly disrupted transport of secretory vesicles, but each drug caused distinct responses on different endosomal populations labeled by ARA6 or ARA7, indicating that a dynamic actin cytoskeleton was critical for some steps in endomembrane trafficking. Our results provide evidence of cross talk between endomembrane trafficking and the actin cytoskeleton in pollen tubes.

Highlights

During polarized growth of pollen tubes, endomembrane trafficking and actin polymerization are two critical processes that establish membrane/wall homeostasis and maintain growth polarity
The growth of pollen tubes is both polar and directional (Hepler et al, 2001); many cellular activities contribute to such growth, the most important being the dynamics of the actin cytoskeleton system, targeted exocytosis, and endocytosis (Hepler et al, 2001)
We show that perturbing actin dynamics by latrunculin B (LatB) or Jas treatments disrupted the V-shaped distribution of transport vesicles, caused aggregation, and dissipation of a subpopulation of endosomes, indicating that actin dynamics are critical at some steps of endomembrane trafficking

Summary

Introduction

During polarized growth of pollen tubes, endomembrane trafficking and actin polymerization are two critical processes that establish membrane/wall homeostasis and maintain growth polarity. We analyzed the effects of drug treatments on Arabidopsis pollen tubes expressing fluorescent protein probes for transport vesicles, endosomes, or the actin cytoskeleton. To study the dynamics of endomembrane trafficking and actin polymerization in Arabidopsis pollen tubes, we generated constructs expressing yellow fluorescent protein (YFP)-fused markers.

Results

Conclusion