The conserved fission complex on peroxisomes and mitochondria

Peroxisome inter-organelle cooperation in Drosophila

Many cellular functions are compartmentalized within the optimized environments of organelles. However, processing or storage of metabolites from the same pathway can occur in multiple organelles. Thus, spatially separated organelles need to cooperate functionally. Coordination between organelles in different specialized cells is also needed, with shared metabolites passed via circulation. Peroxisomes are membrane-bounded organelles responsible for cellular redox and lipid metabolism in eukaryotic cells. Peroxisomes coordinate with other organelles including mitochondria, endoplasmic reticulum, lysosomes, and lipid droplets. This functional coordination requires, or is at least enhanced by, direct contact between peroxisomes and other organelles. Peroxisome dysfunction in humans leads to multiorgan effects including neurological, metabolic, developmental, and age-related diseases. Thus, increased understanding of peroxisome coordination with other organelles, especially cells in various organs is essential. Drosophila melanogaster (fruit fly) has emerged recently as an effective animal model for understanding peroxisomes. Here we review current knowledge of pathways regulating coordination between peroxisomes with other organelles in flies, speculating about analogous roles for conserved Drosophila genes encoding proteins with known organelle coordinating roles in other species.

Mdivi-1 Induced Mitochondrial Fusion as a Potential Mechanism to Enhance Stress Tolerance in Wheat

Simple Summary

Mitochondria play a key role in providing energy to cells. This paper is dedicated to elucidating mitochondria-dependent mechanisms that may enhance abiotic stress tolerance in wheat. Mitochondria are constantly undergoing dynamic processes of fusion and fission. In plants, stressful conditions tend to favor mitochondrial fusion processes. The role of mitochondrial fusion was studied by applying Mdivi-1, an inhibitor of mitochondrial fission, to wheat roots subjected to a wounding stress. Increased mitochondrial functional activity and upregulation of genes involved in energy metabolism suggest that mitochondrial fusion is associated with a general activation of energy metabolism. Controlling mitochondrial fusion rates could change the physiology of wheat plants by altering the energy status of the cell and helping to reduce the effects of stress.

Abstract

Mitochondria play a key role in providing energy to cells. These organelles are constantly undergoing dynamic processes of fusion and fission that change in stressful conditions. The role of mitochondrial fusion in wheat root cells was studied using Mdivi-1, an inhibitor of the mitochondrial fragmentation protein Drp1. The effect of the inhibitor was studied on mitochondrial dynamics in the roots of wheat seedlings subjected to a wounding stress, simulated by excision. Treatment of the stressed roots with the inhibitor increased the size of the mitochondria, enhanced their functional activity, and elevated their membrane potentials. Mitochondrial fusion was accompanied by a decrease in ROS formation and associated cell damage. Exposure to Mdivi-1 also upregulated genes encoding the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and an energy sensor AMP-dependent protein sucrose non-fermenting-related kinase (SnRK1), suggesting that mitochondrial fusion is associated with a general activation of energy metabolism. Controlling mitochondrial fusion rates could change the physiology of wheat plants by altering the energy status of the cell and helping to mitigate the effects of stress.

The isothiocyanate sulforaphane induces respiratory burst oxidase homologue D-dependent reactive oxygen species production and regulates expression of stress response genes

Sulforaphane (SFN) is an isothiocyanate-type phytomolecule present in crucifers, which is mainly synthesized in response to biotic stress. In animals, SFN incorporated in the diet has anticancer properties among others. The mechanism of action and signaling are well described in animals; however, little is known in plants. The goal in the present study is to elucidate components of the SFN signaling pathway, particularly the production of reactive oxygen species (ROS), and its effect on the transcriptome. Our results showed that in Arabidopsis, SFN causes ROS production exclusively through the action of the NADPH oxidase RBOH isoform D that requires calcium as a signaling component for the ROS production. To add to this, we also analyzed the effect of SFN on the transcriptome by RNAseq. We observed the highest expression increase for heat shock proteins (HSP) genes and also for genes associated with the response to oxidative stress. The upregulation of several genes linked to the biotic stress response confirms the interplay between SFN and this stress. In addition, SFN increases the levels of transcripts related to the response to abiotic stress, as well as phytohormones. Taken together, these results indicate that SFN induces an oxidative burst leading to signaling events. This oxidative burst may cause the increase of the expression of genes such as heat shock proteins to restore cellular homeostasis and genes that codify possible components of the signaling pathway and putative effectors.

Dynamic interplay between the co-opted Fis1 mitochondrial fission protein and membrane contact site proteins in supporting tombusvirus replication

Plus-stranded RNA viruses have limited coding capacity and have to co-opt numerous pro-viral host factors to support their replication. Many of the co-opted host factors support the biogenesis of the viral replication compartments and the formation of viral replicase complexes on subverted subcellular membrane surfaces. Tomato bushy stunt virus (TBSV) exploits peroxisomal membranes, whereas the closely-related carnation Italian ringspot virus (CIRV) hijacks the outer membranes of mitochondria. How these organellar membranes can be recruited into pro-viral roles is not completely understood. Here, we show that the highly conserved Fis1 mitochondrial fission protein is co-opted by both TBSV and CIRV via direct interactions with the p33/p36 replication proteins. Deletion of FIS1 in yeast or knockdown of the homologous Fis1 in plants inhibits tombusvirus replication. Instead of the canonical function in mitochondrial fission and peroxisome division, the tethering function of Fis1 is exploited by tombusviruses to facilitate the subversion of membrane contact site (MCS) proteins and peroxisomal/mitochondrial membranes for the biogenesis of the replication compartment. We propose that the dynamic interactions of Fis1 with MCS proteins, such as the ER resident VAP tethering proteins, Sac1 PI4P phosphatase and the cytosolic OSBP-like oxysterol-binding proteins, promote the formation and facilitate the stabilization of virus-induced vMCSs, which enrich sterols within the replication compartment. We show that this novel function of Fis1 is exploited by tombusviruses to build nuclease-insensitive viral replication compartment.

Peroxisomes: versatile organelles with diverse roles in plants

Peroxisomes are small, ubiquitous organelles that are delimited by a single membrane and lack genetic material. However, these simple-structured organelles are highly versatile in morphology, abundance and protein content in response to various developmental and environmental cues. In plants, peroxisomes are essential for growth and development and perform diverse metabolic functions, many of which are carried out coordinately by peroxisomes and other organelles physically interacting with peroxisomes. Recent studies have added greatly to our knowledge of peroxisomes, addressing areas such as the diverse proteome, regulation of division and protein import, pexophagy, matrix protein degradation, solute transport, signaling, redox homeostasis and various metabolic and physiological functions. This review summarizes our current understanding of plant peroxisomes, focusing on recent discoveries. Current problems and future efforts required to better understand these organelles are also discussed. An improved understanding of peroxisomes will be important not only to the understanding of eukaryotic cell biology and metabolism, but also to agricultural efforts aimed at improving crop performance and defense.

Genome-Wide Analysis of Dynamin Gene Family in cassava (Manihot esculenta Crantz) and Transcriptional Regulation of Family Members ARC5 in Hormonal Treatments

The Dynamin gene family play a significance role in many physiological processes, especially ARC5 (Accumulation and replication of chloroplasts 5) in the process of plastid division. We performed a genome-wide analysis of the cassava Dynamin family based on the published cassava genome sequence and identified ARC5. 23 cassava Dynamins (MeDynamins) were identified and renamed. 23 MeDynamins were further divided into five major groups based on their structural and phylogenetic characteristics. The segmental duplication events have a significant impact on the expansion of MeDynamins. ARC5 expression analysis showed that there were differences between leaves and roots of cassava at different developmental stages. The tissue-specific expression analysis of the MeDynamins showed that most of MeDynamins were expressed in stem apical meristem and embryogenesis, whereas ARC5 was mainly expressed in leaves. The processing of IAA (Indole-3-acetic Acid) and MeJA (Methyl Jasmonate) verified the prediction results of cis-elements, and ACR5 was closely related to plant growth and positively correlated. It also indicated that high concentrations of MeJA treatment caused the cassava defense mechanism to function in advance. In conclusion, these findings provide basic insights for functional validation of the ARC5 genes in exogenous hormonal treatments.

Peroxisomes in plant reproduction and seed-related development

Peroxisomes are small multi-functional organelles essential for plant development and growth. Plant peroxisomes play various physiological roles, including phytohormone biosynthesis, lipid catabolism, reactive oxygen species metabolism and many others. Mutant analysis demonstrated key roles for peroxisomes in plant reproduction, seed development and germination and post-germinative seedling establishment; however, the underlying mechanisms remain to be fully elucidated. This review summarizes findings that reveal the importance and complexity of the role of peroxisomes in the pertinent processes. The β-oxidation pathway plays a central role, whereas other peroxisomal pathways are also involved. Understanding the biochemical and molecular mechanisms of these peroxisomal functions will be instrumental to the improvement of crop plants.

Artificial import substrates reveal an omnivorous peroxisomal importomer

The peroxisome matrix protein importomer has the remarkable ability to transport oligomeric protein substrates across the bilayer. However, the selectivity and relation between import and overall peroxisome homeostasis remain unclear. Here, we microinject artificial import substrates and employ quantitative microscopy to probe limits and capabilities of the importomer. DNA and polysaccharides are "piggyback" imported when noncovalently bound by a peroxisome targeting signal (PTS)-bearing protein. A dimerization domain that can be tuned to systematically vary the binding dissociation constant (Kd ) shows that a Kd in the millimolar range is sufficient to promote piggyback import. Microinjection of import substrate at high levels results in peroxisome growth and a proportional accumulation of peroxisome membrane proteins (PMPs). However, corresponding PMP mRNAs do not accumulate, suggesting that this response is posttranscriptionally regulated. Together, our data show that the importomer can tolerate diverse macromolecular species. Coupling between matrix import and membrane biogenesis suggests that matrix protein expression levels can be sufficient to regulate peroxisome size.

Proteome of Plant Peroxisomes

Plant peroxisomes are required for a number of fundamental physiological processes, such as primary and secondary metabolism, development and stress response. Indexing the dynamic peroxisome proteome is prerequisite to fully understanding the importance of these organelles. Mass Spectrometry (MS)-based proteome analysis has allowed the identification of novel peroxisomal proteins and pathways in a relatively high-throughput fashion and significantly expanded the list of proteins and biochemical reactions in plant peroxisomes. In this chapter, we summarize the experimental proteomic studies performed in plants, compile a list of ~200 confirmed Arabidopsis peroxisomal proteins, and discuss the diverse plant peroxisome functions with an emphasis on the role of Arabidopsis MS-based proteomics in discovering new peroxisome functions. Many plant peroxisome proteins and biochemical pathways are specific to plants, substantiating the complexity, plasticity and uniqueness of plant peroxisomes. Mapping the full plant peroxisome proteome will provide a knowledge base for the improvement of crop production, quality and stress tolerance.

Fission and Fusion of Plant Mitochondria, and Genome Maintenance

Dynamic changes maintain a multipartite mitochondrial genome meets the changing needs of plant cells.

Unbalanced lipolysis results in lipotoxicity and mitochondrial damage in peroxisome-deficient Pex19 mutants

Peroxisomal dysfunction is often associated with mitochondrial abnormalities for unknown reasons. We found that peroxisomal loss upon Pex19 mutation in Drosophila results in Hnf4 hyperactivation with free fatty acid accumulation and mitochondrial damage as a consequence. Genetic reduction of Hnf4 in Pex19 mutants improves all phenotypes, including lethality.

Inherited peroxisomal biogenesis disorders (PBDs) are characterized by the absence of functional peroxisomes. They are caused by mutations of peroxisomal biogenesis factors encoded by Pex genes, and result in childhood lethality. Owing to the many metabolic functions fulfilled by peroxisomes, PBD pathology is complex and incompletely understood. Besides accumulation of peroxisomal educts (like very-long-chain fatty acids [VLCFAs] or branched-chain fatty acids) and lack of products (like bile acids or plasmalogens), many peroxisomal defects lead to detrimental mitochondrial abnormalities for unknown reasons. We generated Pex19 Drosophila mutants, which recapitulate the hallmarks of PBDs, like absence of peroxisomes, reduced viability, neurodegeneration, mitochondrial abnormalities, and accumulation of VLCFAs. We present a model of hepatocyte nuclear factor 4 (Hnf4)-induced lipotoxicity and accumulation of free fatty acids as the cause for mitochondrial damage in consequence of peroxisome loss in Pex19 mutants. Hyperactive Hnf4 signaling leads to up-regulation of lipase 3 and enzymes for mitochondrial β-oxidation. This results in enhanced lipolysis, elevated concentrations of free fatty acids, maximal β-oxidation, and mitochondrial abnormalities. Increased acid lipase expression and accumulation of free fatty acids are also present in a Pex19-deficient patient skin fibroblast line, suggesting the conservation of key aspects of our findings.

Arabidopsis Forkhead-Associated Domain Protein 3 negatively regulates peroxisome division

Peroxisomes are ubiquitous and dynamic eukaryotic organelles capable of altering their abundance in response to environmental and developmental cues, yet the regulatory mechanism of plant peroxisome division/proliferation is unclear. To identify transcriptional regulators of the peroxisome division factor gene PEX11b, we performed a nuclear pull-down experiment and identified Arabidopsis Forkhead-Associated Domain Protein 3 (FHA3) as a novel protein that binds to the promoter of PEX11b. Our data supported the conclusion that, in contrast to the previously identified HY5 HOMOLOG (HYH) protein that promotes the transcription of PEX11b, FHA3 is a negative regulator of PEX11b expression and peroxisome division.

Sequence and biochemical analysis of Arabidopsis SP1 protein, a regulator of organelle biogenesis

Peroxisomes, chloroplasts, and mitochondria are essential eukaryotic organelles that host a suite of metabolic processes crucial to energy metabolism and development. Regulatory mechanisms of the dynamics and biogenesis of these important organelles have begun to be discovered in plants. We recently showed that, aside from its previously reported role in targeting chloroplast protein import proteins, the Arabidopsis ubiquitin E3 ligase SP1 (suppressor of ppi1 locus1) negatively regulates peroxisome matrix protein import by promoting the ubiquitination and destabilization of PEX13 and possibly PEX14 and other components of the peroxisome protein import apparatus. Here, we compared protein sequence and domain structure of SP1-like proteins in Arabidopsis and their human homolog, Mitochondrial-Anchored Protein Ligase (MAPL). We further characterized SP1 protein in respect to its membrane topology and ubiquitin E3 ligase activity.

An Interactome-Centered Protein Discovery Approach Reveals Novel Components Involved in Mitosome Function and Homeostasis in Giardia lamblia

Protozoan parasites of the genus Giardia are highly prevalent globally, and infect a wide range of vertebrate hosts including humans, with proliferation and pathology restricted to the small intestine. This narrow ecological specialization entailed extensive structural and functional adaptations during host-parasite co-evolution. An example is the streamlined mitosomal proteome with iron-sulphur protein maturation as the only biochemical pathway clearly associated with this organelle. Here, we applied techniques in microscopy and protein biochemistry to investigate the mitosomal membrane proteome in association to mitosome homeostasis. Live cell imaging revealed a highly immobilized array of 30–40 physically distinct mitosome organelles in trophozoites. We provide direct evidence for the single giardial dynamin-related protein as a contributor to mitosomal morphogenesis and homeostasis. To overcome inherent limitations that have hitherto severely hampered the characterization of these unique organelles we applied a novel interaction-based proteome discovery strategy using forward and reverse protein co-immunoprecipitation. This allowed generation of organelle proteome data strictly in a protein-protein interaction context. We built an initial Tom40-centered outer membrane interactome by co-immunoprecipitation experiments, identifying small GTPases, factors with dual mitosome and endoplasmic reticulum (ER) distribution, as well as novel matrix proteins. Through iterative expansion of this protein-protein interaction network, we were able to i) significantly extend this interaction-based mitosomal proteome to include other membrane-associated proteins with possible roles in mitosome morphogenesis and connection to other subcellular compartments, and ii) identify novel matrix proteins which may shed light on mitosome-associated metabolic functions other than Fe-S cluster biogenesis. Functional analysis also revealed conceptual conservation of protein translocation despite the massive divergence and reduction of protein import machinery in Giardia mitosomes.

Organelles with endosymbiotic origin are present in virtually all extant eukaryotes and have undergone considerable remodeling during > 1 billion years of evolution. Highly diverged organelles such as mitosomes or plastids in some parasitic protozoa are the product of extensive secondary reduction. They are sufficiently unique to generate interest as targets for pharmacological intervention, in addition to providing a rich ground for evolutionary cell biologists. The so-called mitochondria-related organelles (MROs) comprise mitosomes and hydrogenosomes, with the former having lost any role in energy metabolism along with the organelle genome. The mitosomes of the intestinal pathogen Giardia lamblia are the most highly reduced MROs known and have proven difficult to investigate because of their extreme divergence and their unique biophysical properties. Here, we implemented a novel strategy aimed at systematic analysis of the organelle proteome by iterative expansion of a protein-protein interaction network. We combined serial forward and reverse co-immunoprecipitations with mass spectrometry analysis, data mining, and validation by subcellular localization and/or functional analysis to generate an interactome network centered on a giardial Tom40 homolog. This iterative ab initio proteome reconstruction provided protein-protein interaction data in addition to identifying novel organelle proteins and functions. Building on this data we generated information on organelle replication, mitosome morphogenesis and organelle dynamics in living cells.

Mosaic nature of the mitochondrial proteome: Implications for the origin and evolution of mitochondria

Comparative studies of the mitochondrial proteome have identified a conserved core of proteins descended from the α-proteobacterial endosymbiont that gave rise to the mitochondrion and was the source of the mitochondrial genome in contemporary eukaryotes. A surprising result of phylogenetic analyses is the relatively small proportion (10-20%) of the mitochondrial proteome displaying a clear α-proteobacterial ancestry. A large fraction of mitochondrial proteins typically has detectable homologs only in other eukaryotes and is presumed to represent proteins that emerged specifically within eukaryotes. A further significant fraction of the mitochondrial proteome consists of proteins with homologs in prokaryotes, but without a robust phylogenetic signal affiliating them with specific prokaryotic lineages. The presumptive evolutionary source of these proteins is quite different in contending models of mitochondrial origin.

Role of Pex11p in Lipid Homeostasis in Yarrowia lipolytica

Peroxisomes are essential organelles in the cells of most eukaryotes, from yeasts to mammals. Their role in β-oxidation is particularly essential in yeasts; for example, in Saccharomyces cerevisiae, fatty acid oxidation takes place solely in peroxisomes. In this species, peroxisome biogenesis occurs when lipids are present in the culture medium, and it involves the Pex11p protein family: ScPex11p, ScPex25p, ScPex27p, and ScPex34p. Yarrowia lipolytica has three Pex11p homologues, which are YALI0C04092p (YlPex11p), YALI0C04565p (YlPex11C), and YALI0D25498p (Pex11/25p). We found that these genes are regulated by oleic acid, and as has been observed in other organisms, YlPEX11 deletion generated giant peroxisomes when mutant yeast were grown in oleic acid medium. Moreover, ΔYlpex11 was unable to grow on fatty acid medium and showed extreme dose-dependent sensitivity to oleic acid. Indeed, when the strain was grown in minimum medium with 0.5% glucose and 3% oleic acid, lipid body lysis and cell death were observed. Cell death and lipid body lysis may be partially explained by an imbalance in the expression of the genes involved in lipid storage, namely, DGA1, DGA2, and LRO1, as well as that of TGL4, which is involved in lipid remobilization. TGL4 deletion and DGA2 overexpression resulted in decreased oleic acid sensitivity and delayed cell death of ΔYlpex11, which probably stemmed from the release of free fatty acids into the cytoplasm. All these results show that YlPex11p plays an important role in lipid homeostasis in Y. lipolytica.

The neomuran revolution and phagotrophic origin of eukaryotes and cilia in the light of intracellular coevolution and a revised tree of life

Three kinds of cells exist with increasingly complex membrane-protein targeting: Unibacteria (Archaebacteria, Posibacteria) with one cytoplasmic membrane (CM); Negibacteria with a two-membrane envelope (inner CM; outer membrane [OM]); eukaryotes with a plasma membrane and topologically distinct endomembranes and peroxisomes. I combine evidence from multigene trees, palaeontology, and cell biology to show that eukaryotes and archaebacteria are sisters, forming the clade neomura that evolved ~1.2 Gy ago from a posibacterium, whose DNA segregation and cell division were destabilized by murein wall loss and rescued by the evolving novel neomuran endoskeleton, histones, cytokinesis, and glycoproteins. Phagotrophy then induced coevolving serial major changes making eukaryote cells, culminating in two dissimilar cilia via a novel gliding-fishing-swimming scenario. I transfer Chloroflexi to Posibacteria, root the universal tree between them and Heliobacteria, and argue that Negibacteria are a clade whose OM, evolving in a green posibacterium, was never lost.

Peroxisomes take shape

Peroxisomes carry out various oxidative reactions that are tightly regulated to adapt to the changing needs of the cell and varying external environments. Accordingly, they are remarkably fluid and can change dramatically in abundance, size, shape and content in response to numerous cues. These dynamics are controlled by multiple aspects of peroxisome biogenesis that are coordinately regulated with each other and with other cellular processes. Ongoing studies are deciphering the diverse molecular mechanisms that underlie biogenesis and how they cooperate to dynamically control peroxisome utility. These important challenges should lead to an understanding of peroxisome dynamics that can be capitalized upon for bioengineering and the development of therapies to improve human health.

Single-membrane-bounded peroxisome division revealed by isolation of dynamin-based machinery

Peroxisomes (microbodies) are ubiquitous single-membrane-bounded organelles and fulfill essential roles in the cellular metabolism. They are found in virtually all eukaryotic cells and basically multiply by division. However, the mechanochemical machinery involved in peroxisome division remains elusive. Here, we first identified the peroxisome-dividing (POD) machinery. We isolated the POD machinery from Cyanidioschyzon merolae, a unicellular red alga containing a single peroxisome. Peroxisomal division in C. merolae can be highly synchronized by light/dark cycles and the microtubule-disrupting agent oryzalin. By proteomic analysis based on the complete genome sequence of C. merolae, we identified a dynamin-related protein 3 (DRP3) ortholog, CmDnm1 (Dnm1), that predominantly accumulated with catalase in the dividing-peroxisome fraction. Immunofluorescence microscopy demonstrated that Dnm1 formed a ring at the division site of the peroxisome. The outlines of the isolated dynamin rings were dimly observed by phase-contrast microscopy and clearly stained for Dnm1. Electron microscopy revealed that the POD machinery was formed at the cytoplasmic side of the equator. Immunoelectron microscopy showed that the POD machinery consisted of an outer dynamin-based ring and an inner filamentous ring. Down-regulation of Dnm1 impaired peroxisomal division. Surprisingly, the same Dnm1 serially controlled peroxisomal division after mitochondrial division. Because genetic deficiencies of Dnm1 orthologs in multiperoxisomal organisms inhibited both mitochondrial and peroxisomal proliferation, it is thought that peroxisomal division by contraction of a dynamin-based machinery is universal among eukaryotes. These findings are useful for understanding the fundamental systems in eukaryotic cells.

Phosphorylation-dependent Pex11p and Fis1p interaction regulates peroxisome division

Pex11p plays a conserved role in peroxisome division. Although Pex11p is phosphorylated, the exact role of this modification was either unknown or confusing. Phosphorylation of Pichia pastoris Pex11p at serine 173 occurs at the peroxisome and is necessary for its interaction with Fis1p, a key protein of the peroxisome division complex.

Peroxisome division is regulated by the conserved peroxin Pex11p. In Saccharomyces cerevisiae (Sc), induction of the phosphoprotein ScPex11p coincides with peroxisome biogenesis. We show that the ScPex11p homologue in Pichia pastoris (PpPex11p) is phosphorylated at serine 173. PpPex11p expression and phosphorylation are induced in oleate and coordinated with peroxisome biogenesis. PpPex11p transits to peroxisomes via the endoplasmic reticulum (ER). PpPex11p is unstable and ER restricted gin pex3Δ and pex19Δ cells, which are impaired in peroxisomal membrane protein biogenesis. In oleate medium, the P. pastoris mutants pex11A (constitutively unphosphorylated; S173A) and pex11D (constitutively phosphorylated; S173D) exhibit juxtaposed elongated peroxisomes (JEPs) and hyperdivided forms, respectively, although protein levels remain unchanged. In contrast with ScPex11p, the ER-to-peroxisome translocation in P. pastoris is phosphorylation independent, and the phosphorylation occurs at the peroxisome. We show that PpPex11p interacts with the peroxisome fission machinery via PpFis1p and is regulated by phosphorylation because PpPex11p and PpPex11Dp interact more strongly with PpFis1p than PpPex11Ap. Neither PpPex11p nor PpFis1p is necessary for peroxisome division in methanol medium. We propose a model for the role of PpPex11p in the regulation of peroxisome division through a phosphorylation-dependent interaction with the fission machinery, providing novel insights into peroxisome morphogenesis.

Fission and proliferation of peroxisomes

Peroxisomes are remarkably dynamic, multifunctional organelles, which react to physiological changes in their cellular environment and adopt their morphology, number, enzyme content and metabolic functions accordingly. At the organelle level, the key molecular machinery controlling peroxisomal membrane elongation and remodeling as well as membrane fission is becoming increasingly established and defined. Key players in peroxisome division are conserved in animals, plants and fungi, and key fission components are shared with mitochondria. However, the physiological stimuli and corresponding signal transduction pathways regulating and modulating peroxisome maintenance and proliferation are, despite a few exceptions, largely unexplored. There is emerging evidence that peroxisomal dynamics and proper regulation of peroxisome number and morphology are crucial for the physiology of the cell, as well as for the pathology of the organism. Here, we discuss several key aspects of peroxisomal fission and proliferation and highlight their association with certain diseases. We address signaling and transcriptional events resulting in peroxisome proliferation, and focus on novel findings concerning the key division components and their interplay. Finally, we present an updated model of peroxisomal growth and division. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of Peroxisomes in Health and Disease.