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General structure of phospholipids and common head groups. PLs contain two fatty acids ester-linked to glycerol at C-1 and C-2, and a polar head group attached at C-3 via a phosphodiester bond. The fatty acids in PLs can vary in carbon group length and saturation degree. The different common polar head groups and charges are indicated. PA, phosphatidic acid; PE, phosphatidylethanolamine; PC, phosphatidylcholine; PS, phosphatidylserine; PG, phosphatidylglycerol; CL, cardiolipin; PI, phosphatidylinositol.
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Many cellular processes critically depend on the membrane composition. In this review, we focus on the biosynthesis and physiological roles of membrane lipids in the plant pathogen Agrobacterium tumefaciens. The major components of A. tumefaciens membranes are the phospholipids (PLs), phosphatidylethanolamine (PE), phosphatidylglycerol, phosphatidy...
Citations
... It has been suggested that signal transduction processes, such as the functionality of the sensor kinase VirA in A. tumefaciens, may be disrupted in PC-depleted mem branes (56), but this hypothesis requires further investigation. Additional support for the connection between PC and membrane-associated signal transduction processes comes from a recent suppressor screen conducted with the S. meliloti PC-deficient mutant (25). ...
Phosphatidylcholine (PC) is critical for the nitrogen-fixing symbiosis between rhizobia and legumes. We characterized three PC biosynthesis pathways in Rhizobium leguminosarum and evaluated their impact on nitrogen fixation in clover nodules. In the presence of choline, a PC synthase catalyzes the condensation of cytidine diphosphate-diacylglycerol with choline to produce PC. In the presence of lyso-PC, acyltransferases acylate this mono-acylated phospholipid to PC. The third pathway relies on phospholipid N-methyltransferases (Pmts), which sequentially methylate phosphatidylethanolamine (PE) through three rounds of methylation, yielding PC via the intermediates monomethyl-PE and dimethyl-PE. In R. leguminosarum, at least three Pmts participate in this methylation cascade. To elucidate the functions of these enzymes, we recombinantly produced and biochemically characterized them. We moved on to determine the phospholipid profiles of R. leguminosarum mutant strains harboring single and combinatorial deletions of PC biosynthesis genes. The cumulative results show that PC production occurs through the combined action of multiple enzymes, each with distinct substrate and product specificities. The methylation pathway emerges as the dominant PC biosynthesis route, and we pinpoint PmtS2, which catalyzes all three methylation steps, as the enzyme responsible for providing adequate PC amounts for a functional nitrogen-fixing symbiosis with clover.
IMPORTANCE
Understanding the molecular mechanisms of symbiotic nitrogen fixation has important implications for sustainable agriculture. The presence of the phospholipid phosphatidylcholine (PC) in the membrane of rhizobia is critical for the establishment of productive nitrogen-fixing root nodules on legume plants. The reasons for the PC requirement are unknown. Here, we employed Rhizobium leguminosarum and clover as model system for a beneficial plant-microbe interaction. We found that R. leguminosarum produces PC by three distinct pathways. The relative contribution of these pathways to PC formation was determined in an array of single, double, and triple mutant strains. Several of the PC biosynthesis enzymes were purified and biochemically characterized. Most importantly, we demonstrated the essential role of PC formation by R. leguminosarum in nitrogen fixation and pinpointed a specific enzyme indispensable for plant-microbe interaction. Our study offers profound insights into bacterial PC biosynthesis and its pivotal role in biological nitrogen fixation.
... The T-pilus is composed of VirB2 arranged in a five-start helical assembly with a positively charged lumen in association with the phosphatidylcholine lipid (2). Indeed, the biogenesis of phosphatidylcholine is critical for the stability of T4SS proteins (1). A mutant deficient in both pmtA and pcs, encoding phospholipid N-methyltransferase and phosphatidylcholine synthase, respectively, required for phosphatidylcholine biosynthesis is nonpathogenic (123). ...
Among plant-associated bacteria, agrobacteria occupy a special place. These bacteria are feared in the field as agricultural pathogens. They cause abnormal growth deformations and significant economic damage to a broad range of plant species. However, these bacteria are revered in the laboratory as models and tools. They are studied to discover and understand basic biological phenomena and used in fundamental plant research and biotechnology. Agrobacterial pathogenicity and capability for transformation are one and the same and rely on functions encoded largely on their oncogenic plasmids. Here, we synthesize a substantial body of elegant work that elucidated agrobacterial virulence mechanisms and described their ecology. We review findings in the context of the natural diversity that has been recently unveiled for agrobacteria and emphasize their genomics and plasmids. We also identify areas of research that can capitalize on recent findings to further transform our understanding of agrobacterial virulence and ecology.
Expected final online publication date for the Annual Review of Phytopathology, Volume 61 is September 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Phosphatidylcholine (PC) synthase has also been identified as a critical virulence factor. 49 However, PC-deficient mutants did not produce T4SS machines and showed no sensitivity to acetosyringone, 50 suggesting that PC-deficiency has an upstream effect on VirA/VirG regulation of the vir operon. ...
Agrobacterium tumefaciens causes crown gall disease in plants by the horizontal transfer of oncogenic DNA. The conjugation is mediated by the VirB/D4 type 4 secretion system (T4SS) that assembles an extracellular filament, the T-pilus, and is involved in mating pair formation between A. tumefaciens and the recipient plant cell. Here, we present a 3 Å cryoelectron microscopy (cryo-EM) structure of the T-pilus solved by helical reconstruction. Our structure reveals that the T-pilus is a stoichiometric assembly of the VirB2 major pilin and phosphatidylglycerol (PG) phospholipid with 5-start helical symmetry. We show that PG head groups and the positively charged Arg 91 residues of VirB2 protomers form extensive electrostatic interactions in the lumen of the T-pilus. Mutagenesis of Arg 91 abolished pilus formation. While our T-pilus structure is architecturally similar to previously published conjugative pili structures, the T-pilus lumen is narrower and positively charged, raising questions of whether the T-pilus is a conduit for ssDNA transfer.
... Given that A. tumefaciens produces a range of unusual lipids (see Aktas et al., 2014;Sohlenkamp and Geiger, 2016 for reviews) and harbors the genetic repertoire for the de novo synthesis of polyisoprenoids and other sterol-related compounds, we raised the question whether its membranes exhibit a lateral segregation and are organized into distinct functional microdomains. By identification and utilization of putative SPFH proteins as markers, we established a protocol for the isolation of DRMs from A. tumefaciens membranes. ...
Cell membranes are not homogenous but compartmentalized into lateral microdomains, which are considered as biochemical reaction centers for various physiological processes in eukaryotes and prokaryotes. Due to their special lipid and protein composition, some of these microdomains are resistant to treatment with non-ionic detergents and can be purified as detergent-resistant membranes (DRMs). Here we report the proteome of DRMs from the Gram-negative phytopathogen Agrobacterium tumefaciens . Using label-free liquid chromatography-tandem mass spectrometry, we identified proteins enriched in DRMs isolated under normal and virulence-mimicking growth conditions. Prominent microdomain marker proteins such as the SPFH (stomatin/prohibitin/flotillin/HflKC) proteins HflK, HflC and Atu3772, along with the protease FtsH were highly enriched in DRMs isolated under any given condition. Moreover, proteins involved in cell envelope biogenesis, transport and secretion, as well as motility- and chemotaxis-associated proteins were overrepresented in DRMs. Most strikingly, we found virulence-associated proteins such as the VirA/VirG two-component system, and the membrane-spanning type IV and type VI secretion systems enriched in DRMs. Fluorescence microscopy of the cellular localization of both secretion systems and of marker proteins was in agreement with the results from the proteomics approach. These findings suggest that virulence traits are micro-compartmentalized into functional microdomains in A. tumefaciens .
... Furthermore, a blood meal containing B. burgdorferi resulted in significantly increased expression of PTDSS1 in the nymphal tick guts (p<0.05) ( Figure 2I), suggesting that PTDSS1 indeed has a critical role during B. burgdorferi colonization of the tick gut. PTDSS1 is involved in phospholipid metabolism and mainly uses L-serine as the phosphatidyl acceptor to generate the anionic lipid phosphatidylserine (PS), which serves as a precursor for phosphatidylethanolamine (PE) and phosphatidylcholine (PC) synthesis ( Figure 2J; Aktas et al., 2014). Importantly, PC is one of the main phospholipids on the cellular membrane of B. burgdorferi (Kerstholt et al., 2020). ...
Adiponectin-mediated pathways contribute to mammalian homeostasis; however, little is known about adiponectin and adiponectin receptor signaling in arthropods. In this study, we demonstrate that Ixodes scapularis ticks have an adiponectin receptor-like protein (ISARL) but lack adiponectin - suggesting activation by alternative pathways. ISARL expression is significantly upregulated in the tick gut after Borrelia burgdorferi infection suggesting that ISARL-signaling may be co-opted by the Lyme disease agent. Consistent with this, RNA interference (RNAi)-mediated silencing of ISARL significantly reduced the B. burgdorferi burden in the tick. RNA-seq-based transcriptomics and RNAi assays demonstrate that ISARL-mediated phospholipid metabolism by phosphatidylserine synthase I is associated with B. burgdorferi survival. Furthermore, the tick complement C1q-like protein 3 interacts with ISARL, and B. burgdorferi facilitates this process. This study identifies a new tick metabolic pathway that is connected to the life cycle of the Lyme disease spirochete.
... Phospholipids, as the principle component of the plasma membrane, maintain cellular fluidity and permeability and play an important role in the maintenance of regular physiological metabolism. As a major phospholipid, PC undergoes hydrolysis and transfer under the action of PLD during fruit senescence, producing PA and another phospholipid, resulting in changes in cell membrane structure and function (Aktas et al., 2014). Intermittent temperature treatment effectively inhibits the degradation of PC, which means that the cell membrane structure can be better protected from damage. ...
Lipids are not only the building blocks of cellular membranes, but also play fundamental roles in photosynthesis, protection, environmental and cellular communication, and energy storage. Lipid metabolism is a dynamic and complicated process that includes lipid biosynthesis, transport, accumulation, turnover, and excretion, acting to regulate plant development and tolerance to various environmental stresses. Understanding how lipid metabolism regulates the development and growth in response to the adverse conditions raises an interesting question. Communication between membrane and storage lipids has been observed during the process, for example, membrane degradation accompanied by oil body accumulation. Recently autophagy has been connected with lipid metabolism in plants under stress conditions. Understanding lipid processes is crucial for engineering crops for better agronomic traits such as biomass and stress tolerance/resilience.
This Research Topic is focused on the function and regulation of lipid metabolism during development and stress response in photosynthetic organisms including plants, algae, and cyanobacteria.
1) Function of lipid metabolism during development and growth:
- Lipid hormones such as steroids regulating development and growth.
- Formation and degradation of lipid droplet, oil body, and plastoglobule.
- Regulatory mechanisms of autophagy in relation to plant growth.
2) Function of lipid metabolism in environmental stress:
- Synthesis and function of lipid messengers under stress.
- Membrane lipid remodeling (e.g. chloroplast and plasma membrane) under stress.
- Biosynthesis and turnover of storage lipids.
- Lipid homeostasis under stress.
- The role of autophagy in lipid remodeling under stress.
3) Biotechnology for engineering lipid-dependent traits in crops and algae:
- Novel techniques for genetic engineering of plant and alga oil products.
- High-throughput methods for lipid or lipid-dependent traits.
- Advanced microscopy for lipid research.
- Polyunsaturated fatty acid synthesis especially w-3 and -6 fatty acids.
... As member of the rhizosphere, A. tumefaciens is commonly known for its ability to infect plants by the transfer of a segment of its own DNA causing crown gall disease (Chilton et al., 1977). In addition to PE, PG and CL, A. tumefaciens displays a rather complex lipid repertoire featuring atypical PLs like PC, amino acid-containing lipids such as ornithine lipids (OLs) and lysyl-PG, and various glycolipids (Wessel et al., 2006;Geske et al., 2013;Aktas et al., 2014;Czolkoss et al., 2016;Groenewold et al., 2019). Importantly, the exact membrane lipid composition plays a critical role in the interaction with the host plant. ...
The bacterial membrane is constantly remodelled in response to environmental conditions and the external supply of precursor molecules. Some bacteria are able to acquire exogenous lyso‐phospholipids and convert them to the corresponding phospholipids. Here we report that some soil‐dwelling bacteria have alternative options to metabolize lyso‐phosphatidylglycerol (L‐PG). We find that the plant‐pathogen Agrobacterium tumefaciens takes up this mono‐acylated phospholipid and converts it to two distinct isoforms of the non‐canonical lipid bis(monoacylglycero)phosphate (BMP). Chromatographic separation and Q‐TOF MS/MS analysis revealed the presence of two possible BMP stereo configurations acylated at either of the free hydroxyl groups of the glycerol head group. BMP accumulated in the inner membrane and did not visibly alter cell morphology and growth behaviour. The plant‐associated bacterium Sinorhizobium meliloti was also able to convert externally provided L‐PG to BMP. Other bacteria like Pseudomonas fluorescens and Escherichia coli metabolized L‐PG after cell disruption, suggesting that BMP production in the natural habitat relies both on dedicated uptake systems and on head‐group acylation enzymes. Overall, our study adds two previously overlooked phospholipids to the repertoire of bacterial membrane lipids and provides evidence for the remarkable condition‐responsive adaptation of bacterial membranes. This article is protected by copyright. All rights reserved.
... The membrane asymmetry presents a constant state of non-equilibrium which is maintained by continuous active processes [25]. Phospholipids are amphiphilic molecules possessing a hydrophilic headgroup and two hydrophobic fatty acid chains [26]. This amphiphilic structure enables their selfassembly whenever dispersed in a polar-apolar medium [27]. ...
The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often accomplished by recreating model membranes that approximate the structure of cellular membranes in a controlled environment, formed using self-assembly principles. The selected method for membrane creation influences the properties of the membrane assembly, including their response to electric fields used for characterizing transmembrane exchanges. When these self-assembled model membranes are combined with electrophysiology, it is possible to exploit their non-physiological mechanics to enable additional measurements of membrane interactions and phenomena. This review describes several common model membranes including liposomes, pore-spanning membranes, solid supported membranes, and emulsion-based membranes, emphasizing their varying structure due to the selected mode of production. Next, electrophysiology techniques that exploit these structures are discussed, including conductance measurements, electrowetting and electrocompression analysis, and electroimpedance spectroscopy. The focus of this review is linking each membrane assembly technique to the properties of the resulting membrane, discussing how these properties enable alternative electrophysiological approaches to measuring membrane characteristics and interactions.
... Phospholipids, as the principle component of the plasma membrane, maintain cellular fluidity and permeability and play an important role in the maintenance of regular physiological metabolism. As a major phospholipid, PC undergoes hydrolysis and transfer under the action of PLD during fruit senescence, producing PA and another phospholipid, resulting in changes in cell membrane structure and function (Aktas et al., 2014). Intermittent temperature treatment effectively inhibits the degradation of PC, which means that the cell membrane structure can be better protected from damage. ...
The change of lipid metabolism is a key point of blueberry fruit after refrigeration. This study was conducted to evaluate the effects of intermittent warming (IW) of “DuKe” blueberry fruit on its shelf life at 20 ± 0.5°C following 30 days of refrigeration. IW-treated fruit showed higher contents of phosphatidylcholine, linoleic acid, and oleic acid but lower contents of phosphatidic acid and palmitic acid compared to controls. Protective effects on the cell membrane were also reflected as inhibition of the activity of phospholipase D and lipoxygenase. The blueberry fruit showed a lower decay and pitting incidence with higher firmness than control. Interestingly, IW increased C-repeat binding transcription factor gene expression, which can induce the expression of genes related to hypothermia tolerance in plant cells at low temperature. These results indicate that IW can prevent damage to the membrane lipids, which occurs by senescence at a low temperature of blueberry fruit.
... Metabolic pathways with more than three reactions were listed here. They included 19 reactions involved in the biosynthesis of odd-carbon acids and cardiolipin (Aktas et al., 2014). ...
The plant pathogen Agrobacterium tumefaciens causes crown gall disease and is a widely used tool for generating transgenic plants owing to its virulence. The pathogenic process involves a shift from an independent to a living form within a host plant. However, comprehensive analyses of metabolites, genes, and reactions contributing to this complex process are lacking. To gain new insights about the pathogenicity from the viewpoints of physiology and cellular metabolism, a genome-scale metabolic model (GSMM) was reconstructed for A. tumefaciens. The model, referred to as iNX1344, contained 1,344 genes, 1,441 reactions, and 1,106 metabolites. It was validated by analyses of in silico cell growth on 39 unique carbon or nitrogen sources and the flux distribution of carbon metabolism. A. tumefaciens metabolic characteristics under three ecological niches were modelled. A high capacity to access and metabolize nutrients is more important for rhizosphere colonization than in the soil, and substantial metabolic changes were detected during the shift from the rhizosphere to tumour environments. Furthermore, by integrating transcriptome data for tumour conditions, significant alterations in central metabolic pathways and secondary metabolite metabolism were identified. Overall, the GSMM and constraint-based analysis could decode the physiological and metabolic features of A. tumefaciens as well as interspecific interactions with hosts, thereby improving our understanding of host adaptation and infection mechanisms.
