A Distinct Pathway for Polar Exocytosis in Plant Cell Wall Formation.

Hao Wang,Angus Ho Yin Law,Xiaohong Zhuang,Liwen Jiang,Xiangfeng Wang,Teng Zhao,Michael M.T Loy,Shengwang Du

doi:10.1104/pp.16.00754

Abstract

Post-Golgi protein sorting and trafficking to the plasma membrane (PM) is generally believed to occur via the trans-Golgi network (TGN). In this study using Nicotiana tabacum pectin methylesterase (NtPPME1) as a marker, we have identified a TGN-independent polar exocytosis pathway that mediates cell wall formation during cell expansion and cytokinesis. Confocal immunofluorescence and immunogold electron microscopy studies demonstrated that Golgi-derived secretory vesicles (GDSVs) labeled by NtPPME1-GFP are distinct from those organelles belonging to the conventional post-Golgi exocytosis pathway. In addition, pharmaceutical treatments, superresolution imaging, and dynamic studies suggest that NtPPME1 follows a polar exocytic process from Golgi-GDSV-PM/cell plate (CP), which is distinct from the conventional Golgi-TGN-PM/CP secretion pathway. Further studies show that ROP1 regulates this specific polar exocytic pathway. Taken together, we have demonstrated an alternative TGN-independent Golgi-to-PM polar exocytic route, which mediates secretion of NtPPME1 for cell wall formation during cell expansion and cytokinesis and is ROP1-dependent.

Highlights

Post-Golgi protein sorting and trafficking to the plasma membrane (PM) is generally believed to occur via the trans-Golgi network (TGN)
Nicotiana tabacum pollen-specific pectin methylesterase (NtPPME1), which is regulated by apical F-actin, plays a key role in pollen tube cell wall formation (Bosch et al, 2005; Bosch and Hepler, 2006; Wang et al, 2013)
The apical localization of NtPPME1-GFP was interrupted after the pharmaceutical treatments, which might be due to pollen tube growth arrest and loss of cell polarity, our results showed that NtPPME1-GFPpositive intracellular compartments were insensitive to Brefeldin A (BFA), wortmannin, and concanamycin A (ConcA) treatments (Fig. 2, A– D) when compared with the responses of the TGN (GFP-AtSCAMP4) and PVC (GFP-AtVSR2) markers (Fig. 2, E–J)

Summary

Introduction

Post-Golgi protein sorting and trafficking to the plasma membrane (PM) is generally believed to occur via the trans-Golgi network (TGN). The conventional view of pollen tube tip growth and cell plate formation is supported by polar exocytic secretion of numerous vesicles (diameter of 60– 100 nm) to the pollen tube tip and phragmoplast areas during cytokinesis These polar exocytic vesicles, which are generally believed to originate from the Golgi apparatus, are delivered to the site of secretion via the cytoskeleton and fuse with the target membrane with the aid of fusion factors (Jurgens, 2005; Backues et al, 2007). Whether these polar exocytic vesicles undergoing post-Golgi trafficking are part of the conventional Golgi-trans-Golgi network (TGN)-PM/CP exocytosis or are derived from some other unidentified exocytic secretion pathway remain unclear. Cell division requires precise regulation and spatial organization of the cytoskeleton for delivery of secretion vesicles to the expanding cell plate (Molendijk et al, 2001)

Methods

Results

Conclusion