Martin-Luther-Universität Halle-Wittenberg

Plant Nutrition 2019

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Abstracts

19/12/2023
Tonni Grube Andersen

The importance of barriers in a functional relationship

Casparian strips (CS) are famous apoplastic barriers situated in the endodermal cell walls where they facilitate control over nutrient uptake. In recent years we have gained a tremendous amount of mechanistic insight into how the CS barrier system is established and how its functions are executed. However, as most of this work is done in the model Arabidopsis thaliana, we know very little of the role of CS in other species. Of particular interest are plants that undergo specialized symbiotic relationships with microbes as this require tight communication with the vasculature – One interesting case are the nodule-forming, nitrogen-fixing legumes where the CS may influence the ability of the plant to respond to N stress. In pursuit to understand this, we investigated CS formation in the symbiosis model Lotus japonicus. Our work identifies and characterize Lotus mutants without CS. Through a number of analyses, we were able to gain detailed insights into how nodule formation is related to root-shoot communication in a barrier dependent manner. Moreover, since the nodules themselves were also devoid of vascular-associated CS, we performed correlative meta transcript- and metabolomic analysis to probe the status of nodule residing bacteriods in situations where flow to-and-from plant tissues were unrestricted. Combined, our work highlights an overlooked importance of CS in establishment of symbiotic relationships and thereby puts focus on the root barrier systems as an intriguing tool for engineered N-fixation.

05/12/2023
Iain Johnston

Avoiding mutational meltdown: dealing with damage to organelle DNA in plants and beyond

Mitochondria and chloroplasts power complex life. Due to their fascinating endosymbiotic history, they retain their own, internal, organelle DNA (oDNA - specifically, mtDNA and cpDNA). This oDNA encodes essential genes for energy transduction. But it's kept in the damaging environment of the organelle, packaged less robustly than nuclear DNA, and prone to replicative error. How do organisms avoid the buildup of mutational damage in oDNA over generations?

In  mammals, a "genetic bottleneck" acts to segregate mtDNA damage during female development. But plants and other eukaryotes don't have the luxury of implementing this bottleneck in the same way. I'll talk about our work exploring how oDNA damage is addressed in these other taxa, connecting bioinformatics and theory with experimental characterisation of organelle dynamics and genetics.

14/11/2023
Christian Schmitz-Linneweber

Granules in the chloroplast – Phase separation in plant organellar RNA metabolism

Phase separation facilitates temporary compartmentalization of biomolecules within cells or organelles by forming reversible, membrane-less granules that can exhibit liquid-like or gel-like properties. These granules often comprise RNA and proteins with intrinsically disordered regions. While phase-separated RNA granules have been characterized in nuclear, cytoplasmic, and mitochondrial compartments, their presence and functional significance in plant organelles remain largely unexplored.
Our research originated from the finding that the chloroplast-specific RNA-binding protein, CP29A, is essential for chloroplast biogenesis at low temperatures. We demonstrate that the prion-like domain (PLD) of CP29A mediates cold resistance and confers the ability to phase-separate, both in vitro and in vivo. These phase-separated droplets exhibit liquid-like properties and localize near chloroplast nucleoids. Importantly, the PLD is necessary for chloroplast RNA splicing and translation under cold conditions. Our results collectively suggest that chloroplast RNA metabolism is compartmentalized and that CP29A acts as a temperature-sensitive regulator to modulates chloroplast RNA metabolism through inducible phase separation. Further emerging examples for phase-separating organellar proteins are discussed.

14/07/2023
Ana Laxalt

Phospholipase C in plant stress and development

Phosphoinositide-specific phospholipase C (PI-PLC) plays an important role in signal transduction during plant development and in the response to various biotic and abiotic stresses. However, how PI-PLCs are regulated and how they control these processes remains to be fully understood. Gene families encode PLC enzymes. The hypothesis is that different PLCs participate in signaling induced by different types stress and during development.
In Arabidopsis, the PI-PLC gene family is composed of nine members (AtPLC1 to AtPLC9), being AtPLC2 the most abundant isoform that gets rapidly phosphorylated upon pathogen recognition. We showed that AtPLC2 is involved in plant defense responses, stomatal closure, gametophyte development and embryogenesis. To unravel the regulatory networks associated with PLCs, we performed an interactome analysis of AtPLC2 using TurboID proximity-dependent biotin labeling. A total of 167 candidates were enriched. Pathway analysis showed a significantly enriched in protein modification, calcium regulation and receptor kinases.
In tomato, the PI-PLC gene family is composed of seven members (SlPLC1 to SlPLC7). Tomato plants transiently silenced in different PLC isoforms showed different susceptibility to pathogens such as Botrytis cinerea, Phytophthora infestans, Cladosporium fulvum, Verticillium dahliae and Pseudomonas syringae. Specifically, virus-induced gene silencing (VIGS) of SlPLC2 resulted in reduced reactive oxygen species (ROS) levels, altered expression of defense-related genes, decreased susceptibility to Botrytis cinerea and Phytophthora infestans, while susceptibility to Pseudomonas syringae remained unchanged. However, assessing the overall plant fitness was limited in transiently silenced plants. Consequently, we employed CRISPR/Cas9 technology to generate transgene-free loss-of-function SlPLC2 mutants in tomatoes. These mutants will allow us to investigate the role of each PLC isoform in plant stress responses and development, aiming to enhance plant resistance against pathogens. Our aim is to generate transgene-free PLC loss-of-function tomato mutants, in order to improve plant resistance to pathogens and to study the role of each PLC on plant stress and development.

04/07/2023
Marc Knight

Calcium signalling in response to stress in plants

Abiotic and biotic environmental stimuli are sensed and transduced by signalling networks in plants leading to an appropriate pattern of protective gene expression.  My lab is interested in how calcium, involved in response to so many different primary signals, can encode specific information to elicit the correct downstream responses.  The calcium signature hypothesis states that different external stimuli elicit unique spatiotemporal patterns of elevations in cellular calcium concentration and thus encode stimulus-specific information that is “read” by plant cells. Through a combination of experimental and mathematical approaches, we have determined how calcium signatures are “decoded” by specific transcription factors to lead to appropriate specific gene expression responses. Our most recent work has found that unique calcium signatures occur when different stresses are applied simultaneously or sequentially, or when a single stress is applied under different environmental conditions. These signatures represent integrated information obtained from different environmental cues together, and are decoded to produce unique gene expression “decisions”.

27/06/2023
Amanda Souza Camara

Rediscovering the chromonema

The definition of the chromonema dates back to the first observations of chromosomes under compound microscopes in the late 19th century. It is a coiled thread of chromatin that compacts chromosomes into little rods. This model of compaction, based solely on light microscopy, endured for several decades and strengthened from the resolution of the DNA double helix, when it seemed reasonable that the DNA would further coil to a more compact structure. But it later received several disbelieves as the old observations seemed to be an artefact of shearing, and the coiling mechanism too elaborate to encompass several length scales. It also disregarded other structural components as topoisomerases and condensin protein complexes, which became as evident as chromatin loops in the organization of chromosomes. Renewing the interest, chromosome conformation capture sequencing (Hi-C) clearly indicated a helical organization of mitotic chromosomes. With polymer simulation, a bottle-brush model was suggested, in which chromatin loops branch out from a helical protein scaffold. After reviewing Hi-C data from mitotic chromosomes of different species and polymer models of loop extrusion and considering the lack of a continuous protein scaffold (as yet unobserved), we propose a refurbished definition of the chromonema as an entity formed by chromatin loops and rather plastic. We hypothesize that a self-coiling mechanism, depending on the properties of the chromonema, can be general to many eukaryotic species, while accounting for its dissimilarities. Our hypothesis relies on entropic effects already known to guide chromosome organization, but further evidence still needs to be collected.

13/06/2023
Alex Costa

Long-distance turgor pressure changes induce local activation of plant glutamate receptor-like channels

In Arabidopsis thaliana, local wounding and herbivore feeding provoke leaf-to-leaf propagating Ca2+ waves that are dependent on the activity of members of the glutamate receptor-like channels (GLRs). In systemic tissues, GLRs are needed to sustain the synthesis of jasmonic acid (JA) with the subsequent activation of JA-dependent signalling response required for the plant acclimation to the perceived stress. Even if the role of GLRs is well established, the mechanism through which they are activated remains unclear. Here we report that in vivo the amino acid-dependent activation of the AtGLR3.3 channel and systemic responses require a functional ligand-binding domain. By combining imaging and genetics we show that leaf mechanical injury, such as wound, burn as well as hypo-osmotic stress in root cells induce the systemic apoplastic increase of L-Glutamate which is largely independent of AtGLR3.3 that is instead required for systemic cytosolic Ca2+ elevation. Moreover, by using a bioelectronic approach we show that the local release of minute concentrations of L-Glutamate in the leaf lamina fails to induce any long-distance Ca2+ waves.

30/05/2023
Markus Teige

Novel roles for Ca2+ as regulator of chloroplast development?

Chloroplasts contain significant amounts of calcium but, so far, the only well-known function of calcium in chloroplasts is the stabilization of the manganese cluster in the oxygen evolving complex at photosystem II. Moreover, the total and free Ca2+ concentration can vary considerably, thus calling for a potential regulatory role. Using a targeted proteomics approach for chloroplast Ca2+-binding proteins, we identified two small chloroplast proteins of unknown function, which are characterized by a remarkable glutamate-rich C-terminal domain. These proteins are highly conserved in the entire green lineage and mutants of those exhibit strong phenotypes related to chloroplast development. Screening for interacting proteins point to a role in RNA metabolism.

23/05/2023
Ralf Oelmüller

Response of the plant cell to degradation of its wall

Cell wall integrity (CWI) maintenance is central for plant cells. Mechanical or chemical distortions, pH changes, or breakdown products of cell wall polysaccharides activate plasma membrane-localized receptors and induce appropriate downstream responses. Microbial interactions alter or destroy the structure of the plant cell wall, connecting CWI maintenance to immune responses. Cellulose is the major polysaccharide in the primary and secondary cell wall, and its breakdown generates short-chain cellooligomers. One of them, cellotriose, activates the malectin domain-containing CELLOOLIGOMER-RECEPTOR KINASE 1 (CORK1) in Arabidopsis. The activated CORK1 induces cytoplasmic Ca2+ elevation, reactive oxygen species (ROS) production, membrane depolarization, mitogen associated protein kinase (MAPK) activation, cellulose synthase phosphorylation, and the regulation of CWI-related genes. Phosphoproteome analyses identified early targets involved in signaling, cellulose synthesis, the endoplasmatic reticulum/Golgi secretory pathway, cell wall repair and immune responses. I will discuss the early phosphorylation events induced by the novel receptor kinase, compare its malectin domain with those of other malectin-receptor kinases, and propose that they might be crucial for balancing CWI/immune and growth responses.

19/04/2023
Christian Fankhauser

Air channels create a directional light signal to regulate hypocotyl phototropism

Phototropism reorients aerial organs towards the light to improve photosynthesis. This response is initiated by blue light receptors called phototropins. A gradient of phototropin activation is believed to trigger asymmetric growth leading to growth re-orientation. However, how a light gradient is established across the stem to initiate phototropism is unclear. Here we show that intercellular air channels are required for an efficient phototropic response. Air channels enhance light scattering in Arabidopsis hypocotyls thereby steepening the light gradient across this photosensitive organ. We identify an embryonically expressed ABC transporter, which shapes the properties of cell walls surrounding air channels. Air channels contribute to efficient gas exchange with the atmosphere, but details about their development are scarce. We identify a key factor in the development of intercellular air channels and establishes the functional importance of these structures in phototropism.

18/04/2023
Hélène Zuber

mRNA uridylation: a multitasking modification in plant RNA metabolism

mRNA uridylation, i. e. uridine addition at mRNA 3’ end, is a prevalent post-transcriptional modification that promotes mRNA degradation. mRNA uridylation is a highly conserved mechanism present in most eukaryotes, from fission yeast to plants and humans. Over the last decade, our team has shown in Arabidopsis that uridylation is a frequent modification that tags the vast majority of mRNAs and that UTP:RNA URIDYLYLTRANSFERASE 1 (URT1) is the main enzyme uridylating mRNAs. URT1 participates in a molecular network connecting several translational repressors/decapping activators and directly interacts with DCP5, a protein that promotes mRNA decapping and participates in the repression of translation. Interestingly, by using Oxford Nanopore Technologies sequencing, we revealed an unsuspected global role of URT1 in shaping poly(A) tail length. URT1 uridylation prevents the accumulation of excessively deadenylated mRNAs, possibly by both favoring their 5’ to 3’ degradation and hindering deadenylation. Importantly, uridylation prevents mRNAs to become a source of illegitimate siRNAs that silence endogenous mRNAs and, therefore protects plants from the severe impact of an uncontrolled siRNA production on growth and development. We are currently investigating the mechanisms underlying mRNA uridylation in developing seeds to understand its consequences on RNA metabolism and seed physiology. Our first results highlight the importance of URT1-dependent mRNA uridylation in shaping the transcriptome during seed maturation. Hence mRNA uridylation may contribute to the establishment of seed agronomical traits.

11/04/2023
Harvey Millar

Stoking the Fire: tracking the
transport, production and use of
pyruvate as it fuels plant respiration

Plant mitochondria must maintain a consistent flow of metabolic substrates to fuel the TCA cycle and the electron transport chain and at the same time enable the characteristic flexibility of central plant metabolism by linking respiratory metabolism with cytosolic biosynthetic pathways. Dozens of mitochondria inner membrane carriers facilitate these interconnections but our understanding of their functions remain limited. For some we give names suggesting we know what they transport based on homology to other eukaryotes or on transport properties of heterologous expressed proteins in artificial lipid bilayers under non-physiological conditions. For many others we have no information indicating their substrates at all. To show just how complicated the real situation is we consider the transport and metabolism of the most fundamental of respiratory substrates - pyruvate. We show how detailed studies of substrate transport, isolated mitochondrial metabolism, in planta metabolomics and metabolic flux studies and interconnected studies of knockout mutants are all needed to understand the mitochondrial pyruvate carrier (MPC) and its role in respiration. We show that MPC1 is not just one of a family of pyruvate transporters but the essential subunit of all plant mitochondrial pyruvate transport complexes in Arabidopsis. But it is only one of three pathways to provide pyruvate for the TCA cycle. Removal of each by mutation shows the flexibility of plant metabolism to ensure respiratory rate and plant growth. Following up on our studies of MPC1, we have discovered two metabolically separate pools of pyruvate appear to exist inside plant mitochondria, one derived from pyruvate import via MPC1 and destined for pyruvate dehydrogenase complex and the TCA cycle, and another pyruvate pool produced by matrix enzymes and destined for export from plant mitochondria. Understanding the ‘mitochondrial transportome’ in planta and how it constrains mitochondrial function within compartmented central metabolism remains a significant task for the years ahead.

26/01/2023
Gesa Hoffmann

Stress & Granules - the regulation of Cauliflower mosaic virus disease in Arabidopsis thaliana

Cytoplasmic  mRNAs are channelled between ribosomes and phase-separated RNA granules  in a triage between translation, storage, and degradation. Several  types of RNA granules were identified, with the prominent processing  bodies (PBs) and stress granules (SGs) emerging as essential hubs for  RNA regulation during viral infections. Plant viruses impose  extraordinary RNA stress on cells, challenging the RNA surveillance  machineries through their massive production of RNAs during replication  and manipulating the number and nature of RNA granules. We use  Cauliflower mosaic virus (CaMV) to study the role of PBs and SGs during  DNA virus infection and examine how CaMV manoeuvres between RNA  decapping, RNA silencing, nonsense-mediated decay, and translation. CaMV  produces distinct inclusion bodies where viral translation and  replication occurs. Several canonical RNA granule proteins are coopted  into these viral inclusions during infection where they shape disease  outcomes. Among the re-localized proteins are components of the  decapping machinery. Surprisingly, their canonical functions of  decapping and RNA degradation are not acting on the viral RNA. On the  contrary, they enhance the translation efficiency of viral RNA through  an unconventional way.

13/12/2022
Barry D. Bruce

Evolution of Photosystem I: Symmetry, Serendipity, and Speculation

Many, if not most, membrane proteins occur in some oligomeric form. This was first observed for bacteriorhodopsin, the first protein to have its structure determined. In photosynthesis, all the major protein complexes have been observed to form multimers, with the PSII, b6/f, and ATPase complexes all observed as dimers. This organization seems to be conserved from prokaryotes to eukaryotes. However, Photosystem I has been observed to exist in two alternative forms: a trimeric structure in cyanobacteria and a monomeric structure in plants and algae. Although this general observation held for almost 30 years, novel tetrameric forms of PSI were recently detected in two unrelated cyanobacteria, Anabaena sp. PCC 7120 (Nostoc) and Chroococcidiopsis p. TS-821. We have expanded this investigation to over 60 cyanobacteria and shown that tetrameric organization is widespread and found in a large group of cyanobacteria we call the Heterocyst-forming cyanobacteria Close Relatives (HCR). Genomic analysis of HCR indicates an alternative organization of the PSI genes and some subtle changes in the PsaL protein sequence. In some organisms, more than one PsaL gene exists, suggesting multiple PSI forms may co-exist in a single cyanobacterium. We were the first to show that the tetramer is a dimer-ofdimers. We have also demonstrated that growth in high induces a shift from the dimeric to tetrameric, as well as an increase in the synthesis of novel carotenoids. The light-induced change suggests that the tetrameric form may be an early adaptation to growing in high-light habitats. The recent observation that the Glaucophyte, Cyanophora paradoxa, contains a tetrameric structure of PSI suggests that this transition from trimer to tetramer may be an early adaption that preceded chloroplast evolution.

29/11/2022
Mayank Sharma

MFP1 and the coiled-coil saga of starch granule initiation

Starch is one of the major carbohydrate storage compounds in plants. The biogenesis of starch granules can be subdivided into two sequential processes: 1., the formation of granule initials and 2., their subsequent expansion. While much is known about the mechanisms of starch biosynthesis, ultimately leading to granule expansion, the phenomenon of granule initiation is still being explored. Recently, several plastidial coiled-coil domain-containing proteins have been discovered and implicated with the process of starch granule initiation. Mutant plants lacking one or more of these proteins produce fewer starch granules per chloroplast, and the granules are often abnormal in size and/or morphology compared to those of wild-type plants. It is still poorly understood how these proteins organize themselves and coordinate with each other to synthesize granule initials within the chloroplasts. MAR-binding filament protein 1 (MFP1) is one such protein involved in this granule initiation process. MFP1 is the only initiation protein directly associated with the thylakoids and also regulates the membrane association of its partner Protein targeted to starch 2 (PTST2), another crucial protein involved in starch granule initiation. To test if MFP1 determines the location of starch granule biogenesis, we designed and expressed a series of MFP1 variants 'mis'targeted to distinct chloroplast sub-compartments. The results will be presented and signify that MFP1 is indeed one of the main factors responsible for the formation of starch granules at specific locations within the chloroplasts.

13/09/2022
Doron Shkolnik

Calcium-mediated mechanisms of plant response to salt stress during germination and seedling establishment

Salinity impairs plant seed germination and seedling establishment. The calcium ion (Ca2+) which functions as a ubiquitous second messenger in multiple plant responses to various internal and external stimuli, including exposure to salt (NaCl), is known to improve seed germination and seedling growth and development under salt stress conditions. However, the Ca2+-mediated mechanism that underlies the improved tolerance to salt stress is yet to be deciphered. The research focuses on the involvement of the Arabidopsis Na+/K+ transporter HKT1;1 in germinating seedlings response to salt stress. In contrast to wild type, seeds of hkt1 mutants were found as non-responsive to CaCl2 treatment under salt stress conditions, suggesting a role of HKT1;1 in Ca2+-mediated improved tolerance. Promoter activity assay using the GUS reporter gene (HKT1;1promoter-GUS) of seedlings that were treated with NaCl or NaCl + CaCl2 showed enhanced expression of HKT1;1 in the radicle in response to the combined treatment. Ion content analysis revealed higher concentration of K+ in seedlings, that were treated with the combined treatment than just with NaCl, suggesting that the Ca2+- mediated tolerance involves improved accumulation of K+. By employing transcriptome analysis, we identified the Type 2C protein phosphatase PP2C49 that is known to regulate the activity of HKT1;1, as upregulated in response to CaCl2 treatment. Collectively, the findings suggest that Ca2+ enhances the expression of HKT1;1 in the emerging radicle that results in improved accumulation of K+ which allows germination in the presence of relatively high concentrations of salt.

28/06/2022
Martina Ried

Early signaling events in plant root endosymbioses

A tightly regulated nutrient homeostasis is vital for every cell. Plants have evolved elaborate systems to sense and signal extracellular and intracellular e.g. phosphate and nitrogen levels and to regulate cellular nutrient concentrations. Most land plants establish Arbuscular Mycorrhiza with phosphate-acquiring fungi, and selected members of the Fabales, Fagales, Cucurbitales and Rosales engage in root nodule symbiosis with diazotrophic bacteria. While many genes involved in symbiont perception and subsequent genetic reprogramming have been identified and well characterized, the signaling events that take place between the plasma membrane and the nucleus during the establishment of a successful symbiosis and the signaling hubs connecting symbiosis with nutrient homeostasis remain largely obscure. There is accumulating evidence that nutrient homeostasis is regulated by negatively charged inositol pyrophosphates (PP-InsPs). PP-InsPs serve as ligands for SPX domains - eukaryotic sensors that contain a large positively charged surface - and binding of PP-InsPs to SPX enables them to interact with their target proteins, which regulate e.g. phosphate homeostasis. It is our goal to scrutinize the role of PP-InsP ligands and putative precursors during symbiosis and nutrient homeostasis in Lotus japonicus and thus to illuminate the interplay of these different plant strategies to overcome nutrient limitations.


14/06/2022
Iris Finkemeier

Shedding new light on protein modifications in plant metabolism

Dark-to-light transitions, as plants regularly experience, have a profound impact on their metabolic fluxes. With the onset of photosynthesis during dawn, pyruvate-driven TCA cycle activity is inhibited due to the phosphorylation-dependent inactivation of the mitochondrial pyruvate dehydrogenase complex. At the same time glycolysis is inhibited and photorespiratory metabolism may be induced. The mitochondrial tricarboxylic acid cycle is then required to support nitrogen assimilation in chloroplasts. While several key metabolic enzymes are already known to be regulated by light-dependent redox regulation and phosphorylation, the larger picture of metabolic regulation through post-translational modifications (PTM) changes remains fragmentary. Here I will present an overview our most recent insights in the light-dependent PTMome changes in Arabidopsis leaves.


24/05/2022
Piotr Ziolkowski

Many faces of the crossover control in Arabidopsis meiosis

During meiosis homologous chromosomes pair and reciprocally exchange their fragments in a process called crossover. This is required for proper chromosome segregation and for reshuffling of genetic information from both parents. Due to its significance, crossover number and spatial distribution along the chromosome are tightly controlled. In my talk I will discuss current progress on our understanding of the crossover control in eukaryotes with a special focus on Arabidopsis. I will present our data on identification of crossover modifiers – genes, which can affect the crossover frequency or distribution in a genome-wide scale. I will also show how DNA polymorphisms between the homologous chromosomes affect crossover distribution at the chromosome and fine scale. Finally, I will briefly discuss the perspective of application of this knowledge for developing of new plant breeding strategies.


07/06/2022
Patrick Bienert

Metalloids: The Yin and Yang for crop production and healthy nutrition – molecular mechanisms regulating metalloid efficiency

Metalloids encompass a group of biologically important elements ranging from the essential (boron, B) to the highly toxic (arsenic, As). Consequently, all organisms require efficient regulatory systems to control their mineral metalloid status. Boron, Si and As share the same Nodulin26-like Intrinsic Protein (NIP)-mediated transport pathways. We aim at generating NIP transporters which are permeable to B but not to the toxic mineral As. To this aim, we are employing targeted and non-targeted mutational approaches and allele mining combined with transport studies in heterologous expression systems. Excitingly, we identified a NIP isoform which is B specific. In this context, we were able to unravel the functional evolution of NIPs along the phylogeny of land plants. We provided genetic and functional evidence that the horizontal gene transfer of NIP genes from bacteria to plants allowed for a subsequent stepwise functional diversification and neo- functionalization which finally turned bacterial As efflux channels into essential plant B/Si nutrient importers.

Identifying transport-unrelated B efficiency mechanisms in plants has historically proven difficult, largely because of experimental difficulties. In response, we developed systems to study genotypic effects on plant development in repeatable B-deficient conditions. Precise tailoring of this system enabled us to identify B-efficiency mechanisms and their underlying loci in the highly B demanding plants, oilseed-rape (B. napus) and Arabidopsis by QTL and GWAS analyses respectively.


09/05/2022
Roland Lill

Mechanisms of Fe/S protein biogenesis in mitochondria and cytosol of eukaryotes

Iron-sulfur (Fe/S) proteins are involved in numerous important cellular processes such as respiration, metabolism, genome maintenance, protein translation and antiviral response. The synthesis of Fe/S clusters and their assembly into apoproteins in (non-green) eukaryotes is a complex process involving more than 30 proteins located in mitochondria and cytosol. Biogenesis of mitochondrial [2Fe-2S] and [4Fe-4S] proteins is accomplished by the iron-sulfur cluster assembly (ISC) machinery which was inherited from bacteria during evolution [1]. Cytosolic and nuclear Fe/S protein assembly also depends on the function of this machinery, yet additionally requires the mitochondrial ABC exporter ABCB7 and the cytosolic iron-sulfur protein assembly (CIA) machinery [2]. Interestingly, mitochondrial Fe/S protein biogenesis co-evolved with the existence of the entire organelle, defining this process as both the minimal and essential function of mitochondria or related mitosomes and hydrogenosomes [3]. A combination of in vivo and in vitro studies provided a decent picture of the general outline of Fe/S protein biogenesis. Detailed molecular mechanisms underlying the individual reaction steps are currently elucidated by using cell biological, biochemical, biophysical, and ultrastructural approaches. The presentation will provide some of our recent insights into the molecular mechanisms of cellular Fe/S protein maturation and function. This will include i) the de novo synthesis of the [2Fe-2S] cluster on the mitochondrial scaffold protein ISCU2, ii) the mechanisms underlying reductive fusion of two [2Fe-2S] to one [4Fe-4S] cluster on the mitochondrial ISCA proteins, and iii) the role of mitochondria in Fe/S cluster assembly on cytosolic and nuclear apoproteins by the CIA system. These mechanistic insights may eventually help improving our molecular understanding of the biochemical consequences of numerous “Fe/S diseases” linked to most ISC and recently also some CIA gene mutations [1].

Recent reviews:

1. Lill, R. and S.A. Freibert, Mechanisms of Mitochondrial Iron-Sulfur Protein Biogenesis. Annu Rev Biochem, 2020. 89: p. 471-499.

2. Lill, R., From the discovery to molecular understanding of cellular iron-sulfur protein biogenesis. Biol Chem, 2020. 401(6-7): p. 855-876.

3. Braymer, J.J., et al., Mechanistic concepts of iron-sulfur protein biogenesis in Biology. Biochim Biophys Acta Mol Cell Res, 2021. 1868(1): p. 118863.


14/12/2021
Tonni Grube Andersen

Passage cells and the outer xylem pole: an overlooked highway for root communication?

Most agricultural traits are based on above-ground features (amount of seeds, plant height, weight, etc.). However, the plant-associated underground contains many traits that influence overall plant health. Roots are faced with constant stress both regarding nutrient/water availability and biotic factors such as pathogenic microbes and needs to respond accordingly to survive. The root needs to create the right response at a cellular level, and the amplitude of stress factors varies dramatically across the root system. This requires continuous integration with high resolution. While we have some understanding on how these incredibly complex emerging outputs are coordinated within entire root system, we still don’t understand how this is coordinated on a single-cell-level.

The xylem pole of roots contains specific cells termed “passage cells” which respond to environmental fluctuations and nutrient deficiencies. This suggests that the xylem pole of roots might play an important role in how plants sense and interact with their surroundings in the soil.  In our group, we are intrigued by the function of passage cells as well as the adjacent xylem pole and use this as a model to study how a plastic developmental pattern emerges from (a)biotic communication.

In our group we employ and develop microscopical techniques, near-native physiological setups, microfluidics, single-cell transcript- and translatomics as well as microbiome-based and binary microbiome studies. This allow us to unravel novel spatial aspects of how specialized and multi-partite communication occur between plants, the soil and the associated microbiota.


13/07/2021
Axel Mithöfer

The same dance - different couples: Plant signaling in defense against herbivores and carnivory

Plants belong to the most successful organisms on earth. They are able to recognize, respond to and interact with their (a)biotic environment. Among others, plants react to insect herbivore attack, thereby employing an array of defense strategies. A prerequisite for the onset of such appropriate reactions is the perception of insect-derived cues followed by well-coordinated local and systemic signaling processes. Ca2+-ions and jasmonate phytohormones have been implicated as key messenger in many plant signaling pathways, and step by step we learn more about their specific roles in the regulation of defense against herbivory. The same holds true for systemic signals that can be detected within the plant.

Some plant taxa were able to turn the sword around: They became carnivorous. Although known for 150 years, our knowledge concerning the physiology, biochemistry, and molecular biology of plant carnivory is still limited. Only in recent years, -omics analyses have been started, signaling pathways have been identified. I will present data about prey recognition, signaling, composition of digestive fluids concerning proteins as well as secondary metabolites; finally I will discuss general aspects of the plant carnivorous syndrome with respect to plant defense mechanisms.


13/04/2021
Till Ischebeck

Identification of a lipid droplet-plasma membrane tethering complex in Arabidopsis

Lipid droplets (LDs, also referred to as oleosomes or oil bodies) are unique subcellular compartments consisting of a phospholipidmonolayer surrounding a hydrophobic core of predominantly triacylglycerol and sterol esters. We are using proteomics and microscopy to identify proteins associated with LDs and to study their function. This way we aim to learn more about the subcellular and physiological functions of LDs.

One aspect that we are especially interested in are how LDs interact with other subcellular structures to fulfil their function. One mode of interaction are membrane contact sites (MCS) that allow for the direct exchange of molecules, such as lipids between compartments, but can also serve to tether compartments at specific locations in cells.

We found such a MCS between LDs and the plasma membrane and identified three proteins important for its constitution.


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