A Distinct Pathway for Polar Exocytosis in Plant Cell Wall Formation  

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.

Exocytosis and Endocytosis: Yin-Yang Crosstalk for Sculpting a Dynamic Growing Pollen Tube Tip

“…A recent study of Nicotiana tabacum pollen specific pectin methylesterase 1 (NtPPME1), a key pectin modification enzyme regulating the rigidity of cell wall ( Bosch et al, 2005 ; Wang et al, 2013 , 2016 ), reveals that the polar exocytosis and apical targeting of NtPPME1 are directly mediated Golgi-derived secretion vesicles (GDSVs) which by-pass the TGN in growing pollen tubes. Additionally, the fluorescent signal intensity and apical targeting of NtPPME1-GFP are closely associated with the growth oscillation and polarity switch during the pollen tube growth as illustrated in Figure 2A ( Wang et al, 2013 , 2016 ). Therefore, GDSV is believed to be an alternative type of apical exocytic vesicle governing the polar growth of pollen tubes.…”

“… The yin-yang crosstalk of apical exocytosis and endocytosis during pollen tube tip growth oscillation and guidance. (A) A model of time-lapse images of apical subcellular localization of NtPPME1-GFP during with pollen tube growth oscillation and polarity shift based on the results from previous studies ( Bosch et al, 2005 ; Wang et al, 2013 , 2016 ). (B) A model of time lapse images of tip-focused endocytosis stained by FM4-64 which is derived from previous studies shows that apical endocytosis is closely associated with growth oscillation and polarity re-orientation during pollen tube growth ( Zonia and Munnik, 2008 ; Onelli and Moscatelli, 2013 ).…”

“…Recently, several independent studies using fluorescence recovery after photobleaching (FRAP) of different types of exocytic proteins has demonstrated that exocytosis takes place in the apex region, the same region as for endocytosis ( Lee et al, 2008 ; Luo et al, 2016 ; Wang et al, 2016 ; Campanale et al, 2017 ; Li et al, 2018 ; Grebnev et al, 2020 ). For example, NtPPME1, a pectic cell wall modification enzyme, is exocytosed and deposited in the apoplast of the pollen tube tip to regulate the rigidity of pollen tube tip cell wall.…”

Once for All: A Novel Robust System for Co-expression of Multiple Chimeric Fluorescent Fusion Proteins in Plants

“…The DNA templates are derived from previous studies (Wang et al, 2011b, 2016). Then, the first-round PCR products above were mixed and subjected to the optimized isothermal assembly reaction at 50°C for 60 min, followed by amplifying the entire expression cassette using the reaction product as template with the outermost primers (e.g., 1-FP35S and 1-RNOS for expression cassette 1).…”

Phragmoplast microtubule dynamics – a game of zones

“…Many oligosaccharide-modifying enzymes are also located in the midzone, which indicates that oligosaccharides like the membraneundergo remodeling in the course of cell plate shaping. These enzymes include the endo-1,4-β-glucanase KORRIGAN, which digests cellulose fibers (Zuo et al, 2000), and endoxyloglucan transferase that remodels the hemicellulose network by catalyzing splitting and grafting of xyloglucan polymers (Nishitani, 1995), as well as pectin methylesterase, which controls stiffness of the cell wall by modifying pectin (Wang et al, 2016). The main function of the transition zone is therefore to advance cell plate biogenesis from its initiation to the tubular network stage (Segui-Simarro et al, 2004).…”