The Actin Cytoskeleton: Functional Arrays for Cytoplasmic Organization and Cell Shape Control

Actin Cytoskeleton as Actor in Upstream and Downstream of Calcium Signaling in Plant Cells

In plant cells, calcium (Ca²⁺) serves as a versatile intracellular messenger, participating in several fundamental and important biological processes. Recent studies have shown that the actin cytoskeleton is not only an upstream regulator of Ca²⁺ signaling, but also a downstream regulator. Ca²⁺ has been shown to regulates actin dynamics and rearrangements via different mechanisms in plants, and on this basis, the upstream signaling encoded within the Ca²⁺ transient can be decoded. Moreover, actin dynamics have also been proposed to act as an upstream of Ca²⁺, adjust Ca²⁺ oscillations, and establish cytosolic Ca²⁺ ([Ca²⁺]_cyt) gradients in plant cells. In the current review, we focus on the advances in uncovering the relationship between the actin cytoskeleton and calcium in plant cells and summarize our current understanding of this relationship.

NHX-type Na+(K+)/H+ antiporters are required for TGN/EE trafficking and endosomal ion homeostasis in Arabidopsis

The regulation of ion and pH homeostasis of endomembrane organelles is critical for functional protein trafficking, sorting and modification in eukaryotic cells. pH homeostasis is maintained through the activity of vacuolar H+-ATPases (V-ATPases) pumping protons (H+) into the endomembrane lumen, and counter-action by cation/proton exchangers such as the NHX family of Na+(K+)/H+ exchangers. In plants, V-ATPase activity at the trans-Golgi network/early endosome (TGN/EE) is important for secretory and endocytic trafficking, however the role of the endosomal antiporters NHX5 and NHX6 in endomembrane trafficking is unclear. Here we show through genetic, pharmacological, and live-cell imaging approaches that double knockout of NHX5 and NHX6 results in the impairment of endosome motility, protein recycling at the TGN/EE, but not in the secretion of integral membrane proteins. Furthermore, we report that nhx5 nhx6 mutants are partially insensitive to osmotic swelling of TGN/EE induced by the monovalent cation ionophore monensin, and to late endosomal swelling by the phosphatidylinositol 3/4-kinase inhibitor wortmannin, demonstrating that NHX5 and NHX6 function to regulate the luminal cation composition of endosomes.

Quantitative moss cell biology

Research on mosses has provided answers to many fundamental questions in the life sciences, with the model moss Physcomitrella patens spearheading the field. Recent breakthroughs in cell biology were obtained in the quantification of chlorophyll fluorescence, signalling via calcium waves, the creation of designer organelles, gene identification in cellular reprogramming, reproduction via motile sperm and egg cells, asymmetric cell division, visualization of the actin cytoskeleton, identification of genes responsible for the shift from 2D to 3D growth, the structure and importance of the cell wall, and in the live imaging and modelling of protein networks in general. Highly standardized growth conditions, simplicity of most moss tissues, and an outstandingly efficient gene editing facilitate quantitative moss cell biology.

Actin Bundles in The Pollen Tube

The angiosperm pollen tube delivers two sperm cells into the embryo sac through a unique growth strategy, named tip growth, to accomplish fertilization. A great deal of experiments have demonstrated that actin bundles play a pivotal role in pollen tube tip growth. There are two distinct actin bundle populations in pollen tubes: the long, rather thick actin bundles in the shank and the short, highly dynamic bundles near the apex. With the development of imaging techniques over the last decade, great breakthroughs have been made in understanding the function of actin bundles in pollen tubes, especially short subapical actin bundles. Here, we tried to draw an overall picture of the architecture, functions and underlying regulation mechanism of actin bundles in plant pollen tubes.

Cytoskeletal discoveries in the plant lineage using the moss Physcomitrella patens

Advances in cell biology have been largely driven by pioneering work in model systems, the majority of which are from one major eukaryotic lineage, the opisthokonts. However, with the explosion of genomic information in many lineages, it has become clear that eukaryotes have incredible diversity in many cellular systems, including the cytoskeleton. By identifying model systems in diverse lineages, it may be possible to begin to understand the evolutionary origins of the eukaryotic cytoskeleton. Within the plant lineage, cell biological studies in the model moss, Physcomitrella patens, have over the past decade provided key insights into how the cytoskeleton drives cell and tissue morphology. Here, we review P. patens attributes that make it such a rich resource for cytoskeletal cell biological inquiry and highlight recent key findings with regard to intracellular transport, microtubule-actin interactions, and gene discovery that promises for many years to provide new cytoskeletal players.

Neurokinin 1 receptor promotes rat airway smooth muscle cell migration in asthmatic airway remodelling by enhancing tubulin expression

Background

Airway remodelling is a major contributor to hyper-responsiveness leading to chronic asthma; however, the underlying mechanisms remain unclear. This study aimed to investigate the effects of a neurokinin 1 receptor (NK1R) antagonist (WIN62577) on the migration of airway smooth muscle cells (ASMCs) and the expression of NK1R and alpha-tubulin in airway remodelling using young rats with asthma.

Methods

Sprague-Dawley rats were randomly divided into a control group and airway remodelling group. Rats in the model group were stimulated with ovalbumin for 8 weeks. Primary ASMCs were cultured and purified from all rats, and then treated with different doses of WIN62577. The expression of NK1R and α-tubulin in ASMCs was assessed using immunofluorescence, real-time quantitative polymerase chain reaction, and western blotting. Changes in ASMC migration were detected by a transwell chamber assay.

Results

The transwell assay showed that the number of migrating ASMCs in the asthmatic airway remodelling group was significantly greater than that in the control group (P<0.01), which was inhibited by WIN62577 in a dose-dependent manner, with peak inhibition detected at 10^-8 mol/L. The mRNA and protein expression levels of NK1R and α-tubulin were significantly higher in the asthmatic airway remodelling group than in the control group (P<0.05 and P<0.01, respectively), and were significantly decreased after treatment with WIN62577 (P<0.01 and P<0.05, respectively).

Conclusions

NK1R antagonists may suppress ASMC migration in a rat model of airway remodelling by inhibiting tubulin expression, indicating a new potential target for the treatment and control of chronic asthma.

Diffuse Growth of Plant Cell Walls

Structural and functional roles of cellulose, xyloglucan, and pectins in cell wall enlargement are reappraised with insights from mechanics, atomic force microscopy, and other methods.

Finite Element Modeling of Shape Changes in Plant Cells

Mechanical modeling of plant cells using finite element methods serves to simulate the behavior of complex cell shapes with the aim to understand biological functioning

Interplay between Ions, the Cytoskeleton, and Cell Wall Properties during Tip Growth

Tip growth is a focused and tightly regulated apical explosion that depends on the interconnected activities of ions, the cytoskeleton, and the cell wall.