A role for Arabidopsis dynamin related proteins DRP2A/B in endocytosis; DRP2 function is essential for plant growth

Antiviral Mx proteins have an ancient origin and widespread distribution among eukaryotes

Mx proteins, first identified in mammals, encode potent antiviral activity against a wide range of viruses. Mx proteins arose within the Dynamin superfamily of proteins (DSP), which mediate critical cellular processes, such as endocytosis and mitochondrial, plastid, and peroxisomal dynamics. Despite their crucial role, the evolutionary origins of Mx proteins are poorly understood. Through comprehensive phylogenomic analyses with progressively expanded taxonomic sampling, we demonstrate that Mx proteins predate the interferon signaling system in vertebrates. Our analyses find an ancient monophyletic DSP lineage in eukaryotes that groups vertebrate and invertebrate Mx proteins with fungal MxF proteins, the largely uncharacterized plant and algal Dynamin 4A/4C proteins, and representatives from several other eukaryotic lineages, suggesting that Mx-like proteins date back close to the origin of Eukarya. Our phylogenetic analyses also find host-encoded and nucleocytoplasmic large DNA viruses-encoded DSPs interspersed in four distinct DSP lineages, indicating recurrent viral theft of host DSPs. Our analyses thus reveal an ancient history of viral and antiviral functions encoded by the Dynamin superfamily in eukaryotes.

Unravelling DNA methylation dynamics during developmental stages in Quercus ilex subsp. ballota [Desf.] Samp

BACKGROUND

DNA methylation is a critical factor influencing plant growth, adaptability, and phenotypic plasticity. While extensively studied in model and crop species, it remains relatively unexplored in holm oak and other non-domesticated forest trees. This study conducts a comprehensive in-silico mining of DNA methyltransferase and demethylase genes within the holm oak genome to enhance our understanding of this essential process in these understudied species. The expression levels of these genes in adult and seedling leaves, as well as embryos, were analysed using quantitative real-time PCR (qRT-PCR). Global DNA methylation patterns were assessed through methylation-sensitive amplified polymorphism (MSAP) techniques. Furthermore, specific methylated genomic sequences were identified via MSAP sequencing (MSAP-Seq).

RESULT

A total of 13 DNA methyltransferase and three demethylase genes were revealed in the holm oak genome. Expression levels of these genes varied significantly between organs and developmental stages. MSAP analyses revealed a predominance of epigenetic over genetic variation among organs and developmental stages, with significantly higher global DNA methylation levels observed in adult leaves. Embryos exhibited frequent demethylation events, while de novo methylation was prevalent in seedling leaves. Approximately 35% of the genomic sequences identified by MSAP-Seq were methylated, predominantly affecting nuclear genes and intergenic regions, as opposed to repetitive sequences and chloroplast genes. Methylation was found to be more pronounced in the exonic regions of nuclear genes compared to their promoter and intronic regions. The methylated genes were predominantly associated with crucial biological processes such as photosynthesis, ATP synthesis-coupled electron transport, and defence response.

CONCLUSION

This study opens a new research direction in analysing variability in holm oak by evaluating the epigenetic events and mechanisms based on DNA methylation. It sheds light on the enzymatic machinery governing DNA (de)methylation, and the changes in the expression levels of methylases and demethylases in different organs along the developmental stages. The expression level was correlated with the DNA methylation pattern observed, showing the prevalence of de novo methylation and demethylation events in seedlings and embryos, respectively. Several methylated genes involved in the regulation of transposable element silencing, lipid biosynthesis, growth and development, and response to biotic and abiotic stresses are highlighted. MSAP-seq integrated with whole genome bisulphite sequencing and advanced sequencing technologies, such as PacBio or Nanopore, will bring light on epigenetic mechanisms regulating the expression of specific genes and its correlation with the phenotypic variability and the differences in the response to environmental cues, especially those related to climate change.

Antiviral Mx proteins have an ancient origin and widespread distribution among eukaryotes

First identified in mammals, Mx proteins are potent antivirals against a broad swathe of viruses. Mx proteins arose within the Dynamin superfamily of proteins (DSP), mediating critical cellular processes, such as endocytosis and mitochondrial, plastid, and peroxisomal dynamics. And yet, the evolutionary origins of Mx proteins are poorly understood. Using a series of phylogenomic analyses with stepwise increments in taxonomic coverage, we show that Mx proteins predate the interferon signaling system in vertebrates. Our analyses find an ancient monophyletic DSP lineage in eukaryotes that groups vertebrate and invertebrate Mx proteins with previously undescribed fungal MxF proteins, the relatively uncharacterized plant and algal Dynamin 4A/4C proteins, and representatives from several early-branching eukaryotic lineages. Thus, Mx-like proteins date back close to the origin of Eukarya. Our phylogenetic analyses also reveal that host-encoded and NCLDV (nucleocytoplasmic large DNA viruses)-encoded DSPs are interspersed in four distinct DSP lineages, indicating recurrent viral theft of host DSPs. Our analyses thus reveal an ancient history of viral and antiviral functions encoded by the Dynamin superfamily in eukaryotes.

Arabidopsis Dynamin-Related Protein AtDRP2A Contributes to Late Flg22-Signaling and Effective Immunity Against Pseudomonas syringae Bacteria

In eukaryotes, dynamins and dynamin-related proteins (DRPs) are high-molecular weight GTPases responsible for mechanochemical fission of organelles or membranes. Of the six DRP subfamilies in Arabidopsis thaliana, AtDRP1 and AtDRP2 family members serve as endocytic accessory proteins in clathrin-mediated endocytosis. Most studies have focused on AtDRP1A and AtDRP2B as critical modulators of plant pattern-triggered immunity (PTI) against pathogenic, flagellated Pseudomonas syringae pv. tomato DC3000 bacteria and immune signaling in response to the bacterial flagellin peptide flg22. Much less is known about AtDRP2A, the closely related paralog of AtDRP2B. AtDRP2A and AtDRP2B are the only classical, or bona fide, dynamins in Arabidopsis, based on their evolutionary conserved domain structure with mammalian dynamins functioning in endocytosis. AtDRP2B but not AtDRP2A is required for robust ligand-induced endocytosis of the receptor kinase FLAGELLIN SENSING2 for dampening of early flg22 signaling. Here, we utilized Arabidopsis drp2a null mutants to identify AtDRP2A as a positive contributor to effective PTI against P. syringae pv. tomato DC3000 bacteria, consistent with reduced PATHOGEN RELATED1 (PR1) messenger RNA accumulation. We provide evidence that AtDRP2A is a novel modulator of late flg22 signaling, contributing positively to PR1 gene induction but negatively to polyglucan callose deposition. AtDRP2A has no apparent roles in flg22-elicited mitogen-activated protein kinase defense marker gene induction. In summary, this study adds the evolutionary conserved dynamin AtDRP2A to a small group of vesicular trafficking proteins with roles as non-canonical contributors in immune responses, likely due to modulating one or both the localization and activity of multiple different proteins with distinct contributions to immune signaling. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

An Update on the Key Factors Required for Plant Golgi Structure Maintenance

Plant Golgi apparatus serves as the central station of the secretory pathway and is the site where protein modification and cell wall matrix polysaccharides synthesis occur. The polarized and stacked cisternal structure is a prerequisite for Golgi function. Our understanding of Golgi structure maintenance and trafficking are largely obtained from mammals and yeast, yet, plant Golgi has many different aspects. In this review, we summarize the key players in Golgi maintenance demonstrated by genetic studies in plants, which function in ER-Golgi, intra-Golgi and post-Golgi transport pathways. Among these, we emphasize on players in intra-Golgi trafficking.

Creativity comes from interactions: modules of protein interactions in plants

Protein interactions are the foundation of cell biology. For robust signal transduction to occur, proteins interact selectively and modulate their behavior to direct specific biological outcomes. Frequently, modular protein interaction domains are central to these processes. Some of these domains bind proteins bearing post-translational modifications, such as phosphorylation, whereas other domains recognize and bind to specific amino acid motifs. Other modules act as diverse protein interaction scaffolds or can be multifunctional, forming head-to-head homodimers and binding specific peptide sequences or membrane phospholipids. Additionally, the so-called head-to-tail oligomerization domains (SAM, DIX, and PB1) can form extended polymers to regulate diverse aspects of biology. Although the mechanism and structures of these domains are diverse, they are united by their modularity. Together, these domains are versatile and facilitate the evolution of complex protein interaction networks. In this review, we will highlight the role of select modular protein interaction domains in various aspects of plant biology.

Conditional destabilization of the TPLATE complex impairs endocytic internalization

In plants, endocytosis is essential for many developmental and physiological processes, including regulation of growth and development, hormone perception, nutrient uptake, and defense against pathogens. Our toolbox to modulate this process is, however, rather limited. Here, we report a conditional tool to impair endocytosis. We generated a partially functional TPLATE allele by substituting the most conserved domain of the TPLATE subunit of the endocytic TPLATE complex (TPC). This substitution destabilizes TPC and dampens the efficiency of endocytosis. Short-term heat treatment increases TPC destabilization and reversibly delocalizes TPLATE from the plasma membrane to aggregates in the cytoplasm. This blocks FM uptake and causes accumulation of various known endocytic cargoes at the plasma membrane. Short-term heat treatment therefore transforms the partially functional TPLATE allele into an effective conditional tool to impair endocytosis. Next to their role in endocytosis, several TPC subunits are also implicated in actin-regulated autophagosomal degradation. Inactivating TPC via the WDX mutation, however, does not impair autophagy, thus enabling specific and reversible modulation of endocytosis in planta.

Never Walk Alone: Clathrin-Coated Vesicle (CCV) Components in Plant Immunity

At the host-pathogen interface, the protein composition of the plasma membrane (PM) has important implications for how a plant cell perceives and responds to invading microbial pathogens. A plant's ability to modulate its PM composition is critical for regulating the strength, duration, and integration of immune responses. One mechanism by which plant cells reprogram their cell surface is vesicular trafficking, including secretion and endocytosis. These trafficking processes add or remove cargo proteins (such as pattern-recognition receptors, transporters, and other proteins with immune functions) to or from the PM via small, membrane-bound vesicles. Clathrin-coated vesicles (CCVs) that form at the PM and trans-Golgi network/early endosomes have emerged as the prominent vesicle type in the regulation of plant immune responses. In this review, we discuss the roles of the CCV core, adaptors, and accessory components in plant defense signaling and immunity against various microbial pathogens.

Tomato Dynamin Related Protein 2A Associates With LeEIX2 and Enhances PRR Mediated Defense by Modulating Receptor Trafficking

The endocytic trafficking pathway is employed by the plant to regulate immune responses, and is often targeted by pathogen effectors to promote virulence. The model system of the tomato receptor-like protein (RLP) LeEIX2 and its ligand, the elicitor EIX, employs endocytosis to transmit receptor-mediated signals, with some of the signaling events occurring directly from endosomal compartments. Here, to explore the trafficking mechanism of LeEIX2-mediated immune signaling, we used a proteomic approach to identify LeEIX2-associating proteins. We report the identification of SlDRP2A, a dynamin related protein, as an associating partner for LeEIX2. SlDRP2A localizes at the plasma membrane. Overexpression of SlDRP2A increases the sub-population of LeEIX2 in VHAa1 endosomes, and enhances LeEIX2- and FLS2-mediated defense. The effect of SlDRP2A on induction of plant immunity highlights the importance of endomembrane components and endocytosis in signal propagation during plant immune responses.

Genetic Architecture of Soybean Yield and Agronomic Traits

Soybean is the world's leading source of vegetable protein and demand for its seed continues to grow. Breeders have successfully increased soybean yield, but the genetic architecture of yield and key agronomic traits is poorly understood. We developed a 40-mating soybean nested association mapping (NAM) population of 5,600 inbred lines that were characterized by single nucleotide polymorphism (SNP) markers and six agronomic traits in field trials in 22 environments. Analysis of the yield, agronomic, and SNP data revealed 23 significant marker-trait associations for yield, 19 for maturity, 15 for plant height, 17 for plant lodging, and 29 for seed mass. A higher frequency of estimated positive yield alleles was evident from elite founder parents than from exotic founders, although unique desirable alleles from the exotic group were identified, demonstrating the value of expanding the genetic base of US soybean breeding.

Combined 15N-Labeling and TandemMOAC Quantifies Phosphorylation of MAP Kinase Substrates Downstream of MKK7 in Arabidopsis

Reversible protein phosphorylation is a widespread posttranslational modification that plays a key role in eukaryotic signal transduction. Due to the dynamics of protein abundance, low stoichiometry and transient nature of protein phosphorylation, the detection and accurate quantification of substrate phosphorylation by protein kinases remains a challenge in phosphoproteome research. Here, we combine tandem metal-oxide affinity chromatography (tandemMOAC) with stable isotope ¹⁵N metabolic labeling for the measurement and accurate quantification of low abundant, transiently phosphorylated peptides by mass spectrometry. Since tandemMOAC is not biased toward the enrichment of acidophilic, basophilic, or proline-directed kinase substrates, the method is applicable to identify targets of all these three types of protein kinases. The MKK7-MPK3/6 module, for example, is involved in the regulation of plant development and plant basal and systemic immune responses, but little is known about downstream cascade components. Using our here described phosphoproteomics approach we identified several MPK substrates downstream of the MKK7-MPK3/6 phosphorylation cascade in Arabidopsis. The identification and validation of dynamin-related protein 2 as a novel phosphorylation substrate of the MKK7-MPK3/6 module establishes a novel link between MPK signaling and clathrin-mediated vesicle trafficking.

NtDRP is necessary for accurate zygotic division orientation and differentiation of basal cell lineage toward suspensor formation

Plant embryogenesis begins with an asymmetric division of the zygote, producing apical and basal cells with distinct cell fates. The asymmetric zygote division is thought to be critical for embryo pattern formation; however, the molecular mechanisms regulating this process, especially maintaining the accurate position and proper orientation of cell division plane, remain poorly understood. Here, we report that a dynamin-related protein in Nicotiana tabacum, NtDRP, plays a critical role in maintaining orientation of zygotic division plane. Down-regulation of NtDRP caused zygotic cell division to occur in different, incorrect orientations and resulted in disruption of suspensor formation, and even development of twin embryos. The basal cell lineage totally integrated with the apical cell lineage into an embryo-like structure, suggesting that NtDRP is essential to accurate zygotic division orientation and differentiation of basal cell lineage toward suspensor formation. We also reveal that NtDRP plays its role by modulating microtubule spatial organization and spindle orientation during early embryogenesis. Thus, we revealed that NtDRP is involved in orientation of the asymmetric zygotic division and differentiation of distinct suspensor and embryo domains, as well as subsequent embryo pattern formation.

ER network homeostasis is critical for plant endosome streaming and endocytosis

Eukaryotic cells internalize cargo at the plasma membrane via endocytosis, a vital process that is accomplished through a complex network of endosomal organelles. In mammalian cells, the ER is in close association with endosomes and regulates their fission. Nonetheless, the physiological role of such interaction on endocytosis is yet unexplored. Here, we probed the existence of ER–endosome association in plant cells and assayed its physiological role in endocytosis. Through live-cell imaging and electron microscopy studies, we established that endosomes are extensively associated with the plant ER, supporting conservation of interaction between heterotypic organelles in evolutionarily distant kingdoms. Furthermore, by analyzing ER–endosome dynamics in genetic backgrounds with defects in ER structure and movement, we also established that the ER network integrity is necessary for homeostasis of the distribution and streaming of various endosome populations as well as for efficient endocytosis. These results support a novel model that endocytosis homeostasis depends on a spatiotemporal control of the endosome dynamics dictated by the ER membrane network.

Phytophthora infestans RXLR-WY Effector AVR3a Associates with Dynamin-Related Protein 2 Required for Endocytosis of the Plant Pattern Recognition Receptor FLS2

Pathogens utilize effectors to suppress basal plant defense known as PTI (Pathogen-associated molecular pattern-triggered immunity). However, our knowledge of PTI suppression by filamentous plant pathogens, i.e. fungi and oomycetes, remains fragmentary. Previous work revealed that the co-receptor BAK1/SERK3 contributes to basal immunity against the potato pathogen Phytophthora infestans. Moreover BAK1/SERK3 is required for the cell death induced by P. infestans elicitin INF1, a protein with characteristics of PAMPs. The P. infestans host-translocated RXLR-WY effector AVR3a is known to supress INF1-mediated cell death by binding the plant E3 ligase CMPG1. In contrast, AVR3aKI-Y147del, a deletion mutant of the C-terminal tyrosine of AVR3a, fails to bind CMPG1 and does not suppress INF1-mediated cell death. Here, we studied the extent to which AVR3a and its variants perturb additional BAK1/SERK3-dependent PTI responses in N. benthamiana using the elicitor/receptor pair flg22/FLS2 as a model. We found that all tested variants of AVR3a suppress defense responses triggered by flg22 and reduce internalization of activated FLS2. Moreover, we discovered that AVR3a associates with the Dynamin-Related Protein 2 (DRP2), a plant GTPase implicated in receptor-mediated endocytosis. Interestingly, silencing of DRP2 impaired ligand-induced FLS2 internalization but did not affect internalization of the growth receptor BRI1. Our results suggest that AVR3a associates with a key cellular trafficking and membrane-remodeling complex involved in immune receptor-mediated endocytosis. We conclude that AVR3a is a multifunctional effector that can suppress BAK1/SERK3-mediated immunity through at least two different pathways.

Vesicular trafficking and salinity responses in plants

Research spanning three decades has demonstrated that vesicles pinch off from the plasma membrane and traffic through the cytoplasm of plant cells, much as previously reported in animal cells. Although the well-conserved clathrin-mediated mechanism of endocytosis has been well characterized, relatively little is known about clathrin-independent pathways in plants. Modulation of endocytosis by both physical stimuli and chemical ligands has been reported in plants. Here, we review the effect of salinity-one of the most deleterious environmental assaults-on endocytosis and intracellular trafficking.

Arabidopsis dynamin-related protein 1E in sphingolipid-enriched plasma membrane domains is associated with the development of freezing tolerance

The freezing tolerance of Arabidopsis thaliana is enhanced by cold acclimation, resulting in changes in the compositions and function of the plasma membrane. Here, we show that a dynamin-related protein 1E (DRP1E), which is thought to function in the vesicle trafficking pathway in cells, is related to an increase in freezing tolerance during cold acclimation. DRP1E accumulated in sphingolipid and sterol-enriched plasma membrane domains after cold acclimation. Analysis of drp1e mutants clearly showed that DRP1E is required for full development of freezing tolerance after cold acclimation. DRP1E fused with green fluorescent protein was visible as small foci that overlapped with fluorescent dye-labelled plasma membrane, providing evidence that DRP1E localizes non-uniformly in specific areas of the plasma membrane. These results suggest that DRP1E accumulates in sphingolipid and sterol-enriched plasma membrane domains and plays a role in freezing tolerance development during cold acclimation.

Loss of Arabidopsis thaliana Dynamin-Related Protein 2B reveals separation of innate immune signaling pathways

Vesicular trafficking has emerged as an important means by which eukaryotes modulate responses to microbial pathogens, likely by contributing to the correct localization and levels of host components necessary for effective immunity. However, considering the complexity of membrane trafficking in plants, relatively few vesicular trafficking components with functions in plant immunity are known. Here we demonstrate that Arabidopsis thaliana Dynamin-Related Protein 2B (DRP2B), which has been previously implicated in constitutive clathrin-mediated endocytosis (CME), functions in responses to flg22 (the active peptide derivative of bacterial flagellin) and immunity against flagellated bacteria Pseudomonas syringae pv. tomato (Pto) DC3000. Consistent with a role of DRP2B in Pattern-Triggered Immunity (PTI), drp2b null mutant plants also showed increased susceptibility to Pto DC3000 hrcC-, which lacks a functional Type 3 Secretion System, thus is unable to deliver effectors into host cells to suppress PTI. Importantly, analysis of drp2b mutant plants revealed three distinct branches of the flg22-signaling network that differed in their requirement for RESPIRATORY BURST OXIDASE HOMOLOGUE D (RBOHD), the NADPH oxidase responsible for flg22-induced apoplastic reactive oxygen species production. Furthermore, in drp2b, normal MAPK signaling and increased immune responses via the RbohD/Ca2+-branch were not sufficient for promoting robust PR1 mRNA expression nor immunity against Pto DC3000 and Pto DC3000 hrcC-. Based on live-cell imaging studies, flg22-elicited internalization of the plant flagellin-receptor, FLAGELLIN SENSING 2 (FLS2), was found to be partially dependent on DRP2B, but not the closely related protein DRP2A, thus providing genetic evidence for a component, implicated in CME, in ligand-induced endocytosis of FLS2. Reduced trafficking of FLS2 in response to flg22 may contribute in part to the non-canonical combination of immune signaling defects observed in drp2b. In conclusion, this study adds DRP2B to the relatively short list of known vesicular trafficking proteins with roles in flg22-signaling and PTI in plants.

Arabidopsis dynamin-related proteins, DRP2A and DRP2B, function coordinately in post-Golgi trafficking

Dynamin-related proteins (DRPs) are large GTPases involved in a wide range of cellular membrane remodeling processes. In Arabidopsis thaliana, two paralogous land plant-specific type DRPs, DRP2A and DRP2B, are thought to participate in the regulation of post-Golgi trafficking. Here, we examined their molecular properties and functional relationships. qRT-PCR and GUS assays showed that DRP2A and DRP2B were expressed ubiquitously, although their expressions were strongest around root apical meristems and vascular bundles. Yeast two-hybrid, bi-molecular fluorescent complementation, and co-immunoprecipitation mass spectrometry analyses revealed that DRP2A and DRP2B interacted with each other. In observations with confocal laser scanning microscopy and variable incidence angle fluorescent microscopy, fluorescent fusions of DRP2A and DRP2B almost completely co-localized and were mainly localized to endocytic vesicle formation sites of the plasma membrane, clathrin-enriched trans-Golgi network and the cell plate in root epidermal cells. Treatments with wortmannin, an inhibitor of phosphatidylinositol 3-/4-kinases, latrunculin B, an inhibitor of actin polymerization, and oryzalin, an inhibitor of microtubule polymerization, increased the resident time of DRP2A and DRP2B on the plasma membrane. These results show that DRP2A and DRP2B function coordinately in multiple pathways of post-Golgi trafficking in phosphatidylinositol 3- or 4-kinase and cytoskeleton polymerization-dependent manners.

Dynamin-related proteins in plant post-Golgi traffic

Membrane traffic between two organelles begins with the formation of transport vesicles from the donor organelle. Dynamin-related proteins (DRPs), which are large multidomain GTPases, play crucial roles in vesicle formation in post-Golgi traffic. Numerous in vivo and in vitro studies indicate that animal dynamins, which are members of DRP family, assemble into ring- or helix-shaped structures at the neck of a bud site on the donor membrane, where they constrict and sever the neck membrane in a GTP hydrolysis-dependent manner. While much is known about DRP-mediated trafficking in animal cells, little is known about it in plant cells. So far, two structurally distinct subfamilies of plant DRPs (DRP1 and DRP2) have been found to participate in various pathways of post-Golgi traffic. This review summarizes the structural and functional differences between these two DRP subfamilies, focusing on their molecular, cellular and developmental properties. We also discuss the molecular networks underlying the functional machinery centering on these two DRP subfamilies. Furthermore, we hope that this review will provide direction for future studies on the mechanisms of vesicle formation that are not only unique to plants but also common to eukaryotes.

Label-free quantitative proteomic analysis of systemic responses to local wounding and virus infection in Arabidopsis thaliana

Plants are continuously exposed to changing environmental conditions and must, as sessile organisms, possess sophisticated acclimative mechanisms. To gain insight into systemic responses to local virus infection or wounding, we performed comparative LC-MS/MS protein profiling of distal, virus-free leaves four and five days after local inoculation of Arabidopsis thaliana plants with either Oilseed rape mosaic virus (ORMV) or inoculation buffer alone. Our study revealed biomarkers for systemic signaling in response to wounding and compatible virus infection in Arabidopsis, which should prove useful in further addressing the trigger-specific systemic response network and the elusive systemic signals. We observed responses common to ORMV and mock treatment as well as protein profile changes that are specific to local virus infection or mechanical wounding (mock treatment) alone, which provides evidence for the existence of more than one systemic signal to induce these distinct changes. Comparison of the systemic responses between time points indicated that the responses build up over time. Our data indicate stress-specific changes in proteins involved in jasmonic and abscisic acid signaling, intracellular transport, compartmentalization of enzyme activities, protein folding and synthesis, and energy and carbohydrate metabolism. In addition, a virus-triggered systemic signal appears to suppress antiviral host defense.

Cytoskeletal and membrane dynamics during higher plant cytokinesis

Following mitosis, cytoplasm, organelles and genetic material are partitioned into daughter cells through the process of cytokinesis. In somatic cells of higher plants, two cytoskeletal arrays, the preprophase band and the phragmoplast, facilitate the positioning and de novo assembly of the plant-specific cytokinetic organelle, the cell plate, which develops across the division plane and fuses with the parental plasma membrane to yield distinct new cells. The coordination of cytoskeletal and membrane dynamics required to initiate, assemble and shape the cell plate as it grows toward the mother cell cortex is dependent upon a large array of proteins, including molecular motors, membrane tethering, fusion and restructuring factors and biosynthetic, structural and regulatory elements. This review focuses on the temporal and molecular requirements of cytokinesis in somatic cells of higher plants gleaned from recent studies using cell biology, genetics, pharmacology and biochemistry.

Conserved and plant-unique mechanisms regulating plant post-Golgi traffic

Membrane traffic plays crucial roles in diverse aspects of cellular and organelle functions in eukaryotic cells. Molecular machineries regulating each step of membrane traffic including the formation, tethering, and fusion of membrane carriers are largely conserved among various organisms, which suggests that the framework of membrane traffic is commonly shared among eukaryotic lineages. However, in addition to the common components, each organism has also acquired lineage-specific regulatory molecules that may be associated with the lineage-specific diversification of membrane trafficking events. In plants, comparative genomic analyses also indicate that some key machineries of membrane traffic are significantly and specifically diversified. In this review, we summarize recent progress regarding plant-unique regulatory mechanisms for membrane traffic, with a special focus on vesicle formation and fusion components in the post-Golgi trafficking pathway.

Clathrin-mediated endocytosis: the gateway into plant cells

Endocytosis in plants has an essential role not only for basic cellular functions but also for growth and development, hormonal signaling and communication with the environment including nutrient delivery, toxin avoidance, and pathogen defense. The major endocytic mechanism in plants depends on the coat protein clathrin. It starts by clathrin-coated vesicle formation at the plasma membrane, where specific cargoes are recognized and packaged for internalization. Recently, genetic, biochemical and advanced microscopy studies provided initial insights into mechanisms and roles of clathrin-mediated endocytosis in plants. Here we summarize the present state of knowledge and compare mechanisms of clathrin-mediated endocytosis in plants with animal and yeast paradigms as well as review plant-specific regulations and roles of this process.

Membrane traffic and fusion at post-Golgi compartments

Complete sequencing of the Arabidopsis genome a decade ago has facilitated the functional analysis of various biological processes including membrane traffic by which many proteins are delivered to their sites of action and turnover. In particular, membrane traffic between post-Golgi compartments plays an important role in cell signaling, taking care of receptor-ligand interaction and inactivation, which requires secretion, endocytosis, and recycling or targeting to the vacuole for degradation. Here, we discuss recent studies that address the identity of post-Golgi compartments, the machinery involved in traffic and fusion or functionally characterized cargo proteins that are delivered to or pass through post-Golgi compartments. We also provide an outlook on future challenges in this area of research.