Chloroplast Envelope Research Articles

Foliar Pectins and Physiology of Diploid and Autotetraploid Mango Genotypes under Water Stress.

The cultivation of mango in Mediterranean-type climates is challenged by the depletion of freshwater. Polyploids are alternative genotypes with potential greater water use efficiency, but field evaluations of the anatomy and physiology of conspecific adult polyploid trees under water stress remain poorly explored. We combined field anatomical evaluations with measurements of leaf water potential (Ψl) and stomatal conductance (Gs) comparing one diploid and one autotetraploid tree per treatment with and without irrigation during dry summers (when fruits develop). Autotetraploid leaves displayed lower Ψl and Gs in both treatments, but the lack of irrigation only affected Gs. Foliar cells of the adaxial epidermis and the spongy mesophyll contained linear pectin epitopes, whereas branched pectins were localized in the abaxial epidermis, the chloroplast membrane, and the sieve tube elements of the phloem. Cell and fruit organ size was larger in autotetraploid than in diploid mango trees, but the sugar content in the fruits was similar between both cytotypes. Specific cell wall hygroscopic pectins correlate with more stable Ψl of autotetraploid leaves under soil water shortage, keeping lower Gs compared with diploids. These preliminary results point to diploids as more susceptible to water deficits than tetraploids.

Allele-dependent expression and functionality of lipid enzyme phospholipid:diacylglycerol acyltransferase affect diatom carbon storage and growth.

In the acyl-CoA-independent pathway of triacylglycerol (TAG) synthesis unique to plants, fungi, and algae, TAG formation is catalyzed by the enzyme phospholipid:diacylglycerol acyltransferase (PDAT). The unique PDAT gene of the model diatom Phaeodactylum tricornutum strain CCMP2561 boasts 47 single nucleotide variants within protein coding regions of the alleles. To deepen our understanding of TAG synthesis, we observed the allele-specific expression of PDAT by the analysis of 87 published RNA-sequencing (RNA-seq) data and experimental validation. The transcription of one of the two PDAT alleles, Allele 2, could be specifically induced by decreasing nitrogen concentrations. Overexpression of Allele 2 in P. tricornutum substantially enhanced the accumulation of TAG by 44% to 74% under nutrient stress; however, overexpression of Allele 1 resulted in little increase of TAG accumulation. Interestingly, a more serious growth inhibition was observed in the PDAT Allele 1 overexpression strains compared with Allele 2 counterparts. Heterologous expression in yeast (Saccharomyces cerevisiae) showed that enzymes encoded by PDAT Allele 2 but not Allele 1 had TAG biosynthetic activity, and 7 N-terminal and 3 C-terminal amino acid variants between the 2 allele-encoded proteins substantially affected enzymatic activity. P. tricornutum PDAT, localized in the innermost chloroplast membrane, used monogalactosyldiacylglycerol and phosphatidylcholine as acyl donors as demonstrated by the increase of the 2 lipids in PDAT knockout lines, which indicated a common origin in evolution with green algal PDATs. Our study reveals unequal roles among allele-encoded PDATs in mediating carbon storage and growth in response to nitrogen stress and suggests an unsuspected strategy toward lipid and biomass improvement for biotechnological purposes.

Quantifying the Energy Spillover between Photosystems II and I in Cyanobacterial Thylakoid Membranes and Cells.

The spatial separation of photosystems I and II (PSI and PSII) is thought to be essential for efficient photosynthesis by maintaining a balanced flow of excitation energy between them. Unlike the thylakoid membranes of plant chloroplasts, cyanobacterial thylakoids do not form tightly appressed grana stacks that enforce strict lateral separation. The coexistence of the two photosystems provides a ground for spillover-excitation energy transfer from PSII to PSI. Spillover has been considered as a pathway of energy transfer from the phycobilisomes to PSI and may also play a role in state transitions as means to avoid overexcitation of PSII. Here, we demonstrate a significant degree of energy spillover from PSII to PSI in reconstituted membranes and isolated thylakoid membranes of Thermosynechococcus (Thermostichus) vulcanus and Synechocystis sp. PCC 6803 by steady-state and time-resolved fluorescence spectroscopy. The quantum yield of spillover in these systems was determined to be up to 40%. Spillover was also found in intact cells but to a considerably lower degree (20%) than in isolated thylakoid membranes. The findings support a model of coexistence of laterally separated microdomains of PSI and PSII in the cyanobacterial cells as well as domains where the two photosystems are energetically connected. The methodology presented here can be applied to probe spillover in other photosynthetic organisms.

OsPML2, a chloroplast envelope localized transporter is involved in manganese homeostasis in rice

Manganese (Mn), a vital element, plays crucial roles in various biochemical and physiological processes by serving as an essential cofactor for numerous enzymes and acting as a catalytically active metal within biological clusters. In this study, we investigate the role of PHOTOSYNTHESIS-AFFECTED MUTANT 71-LIKE 2 (OsPML2), a member of the UNCHARACTERIZED PROTEIN FAMILY 0016 (UPF0016) family, in regulating Mn homeostasis in rice. OsPML2 was highly expressed in young leaves, ovaries, and stigmas. Cross sections from young leaves revealed that OsPML2 was mainly expressed in the phloem region and mesophyll cells. Furthermore, heterologous expression of OsPML2 restored the growth of Mn uptake-defective yeast strain Δsmf1 under Mn-limited conditions. Subcellular localization analysis demonstrated that OsPML2 was specifically localized in the chloroplast envelope. Knockdown of OsPML2 resulted in reduced chloroplast Mn content, significantly affecting plant growth under Mn deficiency. Furthermore, analysis of isolated thylakoid membranes using blue native gels indicated a compromised accumulation of photosystem II (PSII) complexes in OsPML2 knockdown lines. Additionally, grain yield, grain length, and width were significantly reduced in OsPML2 knockdown plants. Collectively, our findings provide insights into the transport function of OsPML2, which facilitates Mn transport from the cytosol to chloroplast stroma and influences the accumulation of PSII complexes in rice.

Amyloplast sedimentation repolarizes LAZYs to achieve gravity sensing in plants

Gravity controls directional growth of plants, and the classical starch-statolith hypothesis proposed more than a century ago postulates that amyloplast sedimentation in specialized cells initiates gravity sensing, but the molecular mechanism remains uncharacterized. The LAZY proteins are known as key regulators of gravitropism, and lazy mutants show striking gravitropic defects. Here, we report that gravistimulation by reorientation triggers mitogen-activated protein kinase (MAPK) signaling-mediated phosphorylation of Arabidopsis LAZY proteins basally polarized in root columella cells. Phosphorylation of LAZY increases its interaction with several translocons at the outer envelope membrane of chloroplasts (TOC) proteins on the surface of amyloplasts, facilitating enrichment of LAZY proteins on amyloplasts. Amyloplast sedimentation subsequently guides LAZY to relocate to the new lower side of the plasma membrane in columella cells, where LAZY induces asymmetrical auxin distribution and root differential growth. Together, this study provides a molecular interpretation for the starch-statolith hypothesis: the organelle-movement-triggered molecular polarity formation.

Red-Light Transmittance Changes in Variegated Pelargonium zonale-Diurnal Variation in Chloroplast Movement and Photosystem II Efficiency.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark-light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

Bidens pilosa root exudates modulate Pteris multifida gametophyte development: A proteomic investigation

Invasive plant species pose a major threat to native flora, in part due to the allelopathic effects of root exudates. The Novel Weapon Hypothesis (NWH) implicates root exudates as a primary factor for successful take over and destruction of native flora by invasive species. However, the precise mechanisms by which invasive species root exudates mediate this impact are unclear. This study aims to compare and evaluate the specific allelochemical impacts of root exudates from the invasive Bidens pilosa on the native fern Pteris multifida under invasive pressure. Specifically, after 10 days’ exposure, label-free proteomics was applied to analyze the proteins and responsive pathway in Pteris multifida Poir. gametophytes upon exposure to two major Bidens pilosa L. root exudates, undecane and palmitic acid. The data show that 2183 proteins were detected in the untreated Pteris multifida gametophyte; 1911 proteins in the gametophyte treated with the undecane, and 2148 proteins in the gametophyte treated with palmitic acid. After exposure for 10 days, undecane treated gametophytes exhibited morphological anomalies and chlorosis; palmitic acid exposure induced no such effects, although development was delayed relative to the control. Using GO functional protein analysis and KEGG pathways detection, we found that the root exudates played different roles on gammopathy growth. Undecane down regulated fatty acid biosynthesis, damaging the cell and chloroplast membrane, and ultimately leading to cell death. Palmitic acid down regulated flavonoid biosynthesis, compromising the gametophyte photosystem and increasing oxidative stress risk. The specific exudate profiles likely facilitate Bidens pilosa invasion, indicating targeted management of key allelochemicals may mitigate invasive impacts on native species.

Chloroplast clustering around the nucleus induced by OMP24 overexpression unexpectedly promoted PSTVd infection in Nicotiana benthamiana.

Chloroplast clustering around the nucleus is a well-known mechanism that occurs in response to various biotic and abiotic stresses and is believed to be a mechanism of defence against pathogens in plants. This phenomenon is accompanied by increased production of reactive oxygen species (ROS), which can help to destroy invading pathogens. However, the function of chloroplast clustering during viroid infection is unclear. Here, we report that, although the infection by potato spindle tuber viroid (PSTVd) failed to induce chloroplast clustering, chloroplast clustering caused by the overexpression of the Nicotiana benthamiana chloroplast outer membrane protein 24 (NbOMP24) promoted the infection by PSTVd, a viroid pathogen, in N. benthamiana. Interestingly, H2 O2 treatment, which caused increased ROS accumulation, showed no significant effects on PSTVd infection. Moreover, NbOMP24 protein showed no direct interaction with PSTVd. We propose that perinuclear chloroplast clustering induced by NbOMP24 provides a favourable environment for PSTVd infection. These findings highlight the complexity of chloroplast clustering-mediated plant-pathogen interactions and the need for further research to fully understand these mechanisms.

Chloroplast import motor subunits FtsHi1 and FtsHi2 are located on opposite sides of the inner envelope membrane

Protein import into chloroplasts is powered by ATP hydrolysis in the stroma. Establishing the identity and functional mechanism of the stromal ATPase motor that drives import is critical for understanding chloroplast biogenesis. Recently, a complex consisting of Ycf2, FtsHi1, FtsHi2, FtsHi4, FtsHi5, FtsH12, and malate dehydrogenase was shown to be important for chloroplast protein import, and it has been proposed to act as the motor driving protein translocation across the chloroplast envelope into the stroma. To gain further mechanistic understanding of how the motor functions, we performed membrane association and topology analyses on two of its subunits, FtsHi1 and FtsHi2. We isolated cDNA clones encoding FtsHi1 and FtsHi2 preproteins to perform in vitro import experiments in order to determine the exact size of each mature protein. We also generated antibodies against the C-termini of the proteins, i.e., where their ATPase domains reside. Protease treatments and alkaline and high-salt extractions of chloroplasts with imported and endogenous proteins revealed that FtsHi1 is an integral membrane protein with its C-terminal portion located in the intermembrane space of the envelope, not the stroma, whereas FtsHi2 is a soluble protein in the stroma. We further complemented an FtsHi1-knockout mutant with a C-terminally tagged FtsHi1 and obtained identical results for topological analyses. Our data indicate that the model of a single membrane-anchored pulling motor at the stromal side of the inner membrane needs to be revised and suggest that the Ycf2-FtsHi complex may have additional functions.

Effect of NaCl on the Lipid Profile of Detergent-Resistant membranes of the Chloroplasts and Mitochondria of Euhalophyte Plants

The effect of 1 M NaCl on the lipid profile of detergent-resistant chloroplast membranes was studied. sts and mitochondria of salt-accumulating halophyte plants – Salicornia perennans Willd. And Suaeda salsa (L.) Pall. (family Amaranthaceae). The composition of lipids and fatty acids in detergent-resistant membranes differs from the membrane lipids of chloroplasts and mitochondria by a large number of cerebrosides and sterols. Under the given salinity conditions, S. perennans experienced many a fold increase in the proportion of cerebrosides in the composition of detergent-resistant chloroplast membranes, and in S. salsa is found in detergent-resistant mitochondrial membranes. The opposite effect was observed in relation to sterols: a decrease in their relative content under the action of salt. Received data indicate the participation of detergent-resistant membranes in the interaction of chloroplast cells and mitochondria in the cellular response of halophytes to salinity.

Comparative leaf structural analysis of Nepeta nuda l. Plantlets, regenerated from cryopreserved shoot meristem and ex vitro-adapted plants

The leaf anatomy and chloroplast ultrastructure of Nepeta nuda L. plantlets regenerated in vitro from cryopreserved shoot apical meristem and in vitro-micropropagated plantlets were studied comparatively to assess whether cryoprocedure affected leaf morphogenesis. Both postcryo and in vitro plantlets failed to develop a distinguishable palisade layer, making the mesophyll appear homogeneous. Significant damage to the chloroplast envelope and substantial thylakoid ruptures were also observed. We assumed that the specific in vitro conditions more likely affected the structures than the cryotreatment itself. Light and transmission electron microscopy observations were also carried out on newly formed leaves of ex vitro-adapted plants. The examined leaf features were similar to those in the in situ plants – bifacial leaf lamina, double-layered palisade parenchyma, loosely arranged spongy parenchyma cells, and chloroplasts with intact envelope and evenly distributed throughout the stroma internal membrane system. The obtained histological and ultrastructural results revealed the retained morphogenetic potential of N. nuda plants and proved cryopreservation as a suitable method for long-term storage.

Chloroplast-related host proteins interact with NIb and NIa-Pro of soybeans mosaic virus and induce resistance in the susceptible cultivar

To gain a deeper understanding of the molecular mechanisms involved in viral infection and the corresponding plant resistance responses, it is essential to investigate the interactions between viral and host proteins. In the case of viral infections in plants, a significant portion of the affected gene products are closely associated with chloroplasts and photosynthesis. However, the molecular mechanisms underlying the interplay between the virus and host chloroplast proteins during replication remain poorly understood. In our previous study, we made an interesting discovery regarding soybean mosaic virus (SMV) infection in resistant and susceptible soybean cultivars. We found that the photosystem I (PSI) subunit (PSaC) and ATP synthase subunit α (ATPsyn-α) genes were up-regulated in the resistant cultivar following SMV-G7H and SMV-G5H infections compared to the susceptible cultivar. Overexpression of these two genes within the SMV-G7H genome in the susceptible cultivar Lee74 (rsv3-null) reduced SMV accumulation, whereas silencing of the PSaC and ATPsyn-α genes promoted SMV accumulation. We have also found that the PSaC and ATPsyn-α proteins are present in the chloroplast envelope, nucleus, and cytoplasm. Building on these findings, we now characterized protein-protein interactions between PSaC and ATPsyn-α with two viral proteins, NIb and NIa-Pro, respectively, of SMV. Through co-immunoprecipitation (Co-IP) experiments, we confirmed the interactions between these proteins. Moreover, when the C-terminal region of either PSaC or ATPsyn-α was overexpressed in the SMV-G7H genome, we observed a reduction in viral accumulation and systemic infection in the susceptible cultivar. Based on these results, we propose that the PSaC and ATPsyn-α genes play a modulatory role in conferring resistance to SMV infection by influencing the function of NIb and NIa-Pro-in SMV replication and movement. The identification of these photosynthesis-related genes as key players in the interplay between the virus and the host provides valuable insights for developing more targeted control strategies against SMV. Additionally, by utilizing these genes, it may be possible to genetically engineer plants with improved photosynthetic efficiency and enhanced resistance to SMV infection.

Drought and heat stress mediated activation of lipid signaling in plants: a critical review.

Lipids are a principal component of plasma membrane, acting as a protective barrier between the cell and its surroundings. Abiotic stresses such as drought and temperature induce various lipid-dependent signaling responses, and the membrane lipids respond differently to environmental challenges. Recent studies have revealed that lipids serve as signal mediators forreducing stress responses in plant cells and activating defense systems. Signaling lipids, such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, and N-acylethanolamines, are generated in response to stress. Membrane lipids are essential for maintaining the lamellar stack of chloroplasts and stabilizing chloroplast membranes under stress. However, the effects of lipid signaling targets in plants are not fully understood. This review focuses on the synthesis of various signaling lipids and their roles in abiotic stress tolerance responses, providing an essential perspective for further investigation into the interactions between plant lipids and abiotic stress.

Sink-source imbalance triggers delayed photosynthetic induction: Transcriptomic and physiological evidence.

Sink-source imbalance causes accumulation of nonstructural carbohydrates (NSCs) and photosynthetic downregulation. However, despite numerous studies, it remains unclear whether NSC accumulation or N deficiency more directly decreases steady-state maximum photosynthesis and photosynthetic induction, as well as underlying gene expression profiles. We evaluated the relationship between photosynthetic capacity and NSC accumulation induced by cold girdling, sucrose feeding, and low nitrogen treatment in Glycine max and Phaseolus vulgaris. In G. max, changes in transcriptome profiles were further investigated, focusing on the physiological processes of photosynthesis and NSC accumulation. NSC accumulation decreased the maximum photosynthetic capacity and delayed photosynthetic induction in both species. In G. max, such photosynthetic downregulation was explained by coordinated downregulation of photosynthetic genes involved in the Calvin cycle, Rubisco activase, photochemical reactions, and stomatal opening. Furthermore, sink-source imbalance may have triggered a change in the balance of sugar-phosphate translocators in chloroplast membranes, which may have promoted starch accumulation in chloroplasts. Our findings provide an overall picture of photosynthetic downregulation and NSC accumulation in G. max, demonstrating that photosynthetic downregulation is triggered by NSC accumulation and cannot be explained solely by N deficiency.

Gating of β-Barrel Protein Pores, Porins, and Channels: An Old Problem with New Facets.

β barrels are ubiquitous proteins in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. These transmembrane proteins (TMPs) execute a wide variety of tasks. For example, they can serve as transporters, receptors, membrane-bound enzymes, as well as adhesion, structural, and signaling elements. In addition, multimeric β barrels are common structural scaffolds among many pore-forming toxins. Significant progress has been made in understanding the functional, structural, biochemical, and biophysical features of these robust and versatile proteins. One frequently encountered fundamental trait of all β barrels is their voltage-dependent gating. This process consists of reversible or permanent conformational transitions between a large-conductance, highly permeable open state and a low-conductance, solute-restrictive closed state. Several intrinsic molecular mechanisms and environmental factors modulate this universal property of β barrels. This review article outlines the typical signatures of voltage-dependent gating. Moreover, we discuss recent developments leading to a better qualitative understanding of the closure dynamics of these TMPs.

Excess manganese increases photosynthetic activity via enhanced reducing center and antenna plasticity in Chlorella vulgaris

Photosynthesis relies on many easily oxidizable/reducible transition metals found in the metalloenzymes that make up much of the photosynthetic electron transport chain (ETC). One of these is manganese, an essential cofactor of photosystem II (PSII) and a component of the oxygen-evolving complex, the only biological entity capable of oxidizing water. Additionally, manganese is a cofactor in enzymatic antioxidants, notably the superoxide dismutases—which are localized to the chloroplastic membrane. However, unlike other metals found in the photosynthetic ETC, previous research has shown exposure to excess manganese enhances photosynthetic activity rather than diminishing it. In this study, the impact of PSII heterogeneity on overall performance was investigated using chlorophyll fluorescence, a rapid, non-invasive technique that probed for overall photosynthetic efficiency, reducing site activity, and antenna size and distribution. These measurements unveiled an enhanced plasticity of PSII following excess manganese exposure, in which overall performance and reducing center activity increased while antenna size and proportion of PSIIβ centers decreased. This enhanced activity suggests manganese may hold the key to improving photosynthetic efficiency beyond that which is observed in nature.

Ferredoxin C2 is required for chlorophyll biosynthesis and accumulation of photosynthetic antennae in Arabidopsis.

Ferredoxins (Fd) are small iron-sulphur proteins, with sub-types that have evolved for specific redox functions. Ferredoxin C2 (FdC2) proteins are essential Fd homologues conserved in all photosynthetic organisms and a number of different FdC2 functions have been proposed in angiosperms. Here we use RNAi silencing in Arabidopsis thaliana to generate a viable fdC2 mutant line with near-depleted FdC2 protein levels. Mutant leaves have ~50% less chlorophyll a and b, and chloroplasts have poorly developed thylakoid membrane structure. Transcriptomics indicates upregulation of genes involved in stress responses. Although fdC2 antisense plants show increased damage at photosystem II (PSII) when exposed to high light, PSII recovers at the same rate as wild type in the dark. This contradicts literature proposing that FdC2 regulates translation of the D1 subunit of PSII, by binding to psbA transcript. Measurement of chlorophyll biosynthesis intermediates revealed a build-up of Mg-protoporphyrin IX, the substrate of the aerobic cyclase. We localise FdC2 to the inner chloroplast envelope and show that the FdC2 RNAi line has a disproportionately lower protein abundance of antennae proteins, which are nuclear-encoded and must be refolded at the envelope after import.

Responses of differentially expressed proteins and endogenous hormones in winter rapeseed (Brassica rapa L.) roots under water deficit stress

AbstractWinter rapeseed (Brassica rapa L.) can well‐adapt to environmental conditions such as barrenness, water deficit and low temperature in arid and semi‐arid planting regions and is the preferred rapeseed type. In this study, we analysed changes of root system morphology, antioxidant enzyme activity, endogenous hormone contents and differentially expressed proteins (DEPs) under control (CK), slight water deficit (SWD, 50–55% of maximum field water capacity), moderate water deficit (MWD, 40–45% of maximum field water capacity) and high water deficit (HWD, 30–35% of maximum field water capacity) conditions. Winter rapeseed experienced taproot elongation, decreased taproot diameter and increased lateral root number, under water deficit stress. The accumulation of reactive oxygen species (ROS) can cause membrane system peroxidation, and antioxidant enzyme activity increases to remove ROS. Changes in jasmonic acid (JA), salicylic acid (SA), cytokinin (CTK), auxin (IAA) and gibberellin (GA) levels promote the absorption of water and minerals by driving changes in the root system architecture to resist water deficit stress. A proteomic analysis has shown that DEPs are involved in energy metabolism, antioxidation response, osmotic regulation, hormone signal transduction, protein metabolism and the stress response, and these proteins are located in the peroxisome, chloroplast, mitochondrion, cell wall, vacuole, cytoplasm, extracellular space and cell membrane. In this study, multiple DEPs (malate dehydrogenase cytoplasmic 1 OS, 14‐3‐3‐like protein GF14 Psi, GA 3‐beta‐dioxygenase, glutathione reductase and jasmonate‐inducible protein) were involved in the root system architecture, revealing the complexity of the root response to water deficit. Significant/extremely significant synergistic relationships were observed between antioxidant enzyme activity and endogenous hormone contents. In conclusion, ROS, endogenous hormones and stress‐related proteins work synergistically to control the root system architecture of winter rapeseed roots in response to water deficit stress.

Membrane insertases at a glance.

Protein translocases, such as the bacterial SecY complex, the Sec61 complex of the endoplasmic reticulum (ER) and the mitochondrial translocases, facilitate the transport of proteins across membranes. In addition, they catalyze the insertion of integral membrane proteins into the lipid bilayer. Several membrane insertases cooperate with these translocases, thereby promoting the topogenesis, folding and assembly of membrane proteins. Oxa1 and BamA family members serve as core components in the two major classes of membrane insertases. They facilitate the integration of proteins with α-helical transmembrane domains and of β-barrel proteins into lipid bilayers, respectively. Members of the Oxa1 family were initially found in the internal membranes of bacteria, mitochondria and chloroplasts. Recent studies, however, also identified several Oxa1-type insertases in the ER, where they serve as catalytically active core subunits in the ER membrane protein complex (EMC), the guided entry of tail-anchored (GET) and the GET- and EMC-like (GEL) complex. The outer membrane of bacteria, mitochondria and chloroplasts contain β-barrel proteins, which are inserted by members of the BamA family. In this Cell Science at a Glance article and the accompanying poster, we provide an overview of these different types of membrane insertases and discuss their function.

Arabidopsis mutants lacking DLDG1 and non-photochemical quenching-related proteins reveal the regulatory role of DLDG1 in chloroplast pH homeostasis.

The control of pH in chloroplasts is important to regulate photosynthesis, although details of the precise regulatory mechanisms of H+ homeostasis in chloroplasts are not fully understood. We recently found that the cyanobacterial PxcA homolog DLDG1 is involved in plastidial pH control. PxcA and DLDG1 have been thought to control light-dependent H+ extrusion across the cyanobacterial cytoplasmic and chloroplast envelope membranes, respectively. To investigate DLDG1-dependent pH control in chloroplasts, we crossed the dldg1 mutant with various mutants lacking known non-photochemical quenching (NPQ)-related proteins, such as fluctuating-light acclimation protein 1 (FLAP1), PsbS/NPQ4, and proton gradient regulation 5 (PGR5). Phenotypes of these double mutants revealed that PsbS works upstream of DLDG1, PGR5 affects NPQ independently from DLDG1, and the ΔpH regulation by FLAP1 and DLDG1 are independent of each other.