Recent Submissions

  • Journal Article

    Sequence heterochrony led to a gain of functionality in an immature stage of the central complex: A fly–beetle insight 

    Farnworth, Max S.; Eckermann, Kolja N.; Bucher, Gregor
    PLOS Biology 2020; 18(10) p.1-32: Art. e3000881
    Animal behavior is guided by the brain. Therefore, adaptations of brain structure and function are essential for animal survival, and each species differs in such adaptations. The brain of one individual may even differ between life stages, for instance, as adaptation to the divergent needs of larval and adult life of holometabolous insects. All such differences emerge during development, but the cellular mechanisms behind the diversification of brains between taxa and life stages remain enigmatic. In this study, we investigated holometabolous insects in which larvae differ dramatically from the adult in both behavior and morphology. As a consequence, the central complex, mainly responsible for spatial orientation, is conserved between species at the adult stage but differs between larvae and adults of one species as well as between larvae of different taxa. We used genome editing and established transgenic lines to visualize cells expressing the conserved transcription factor retinal homeobox, thereby marking homologous genetic neural lineages in both the fly Drosophila melanogaster and the beetle Tribolium castaneum. This approach allowed us for the first time to compare the development of homologous neural cells between taxa from embryo to the adult. We found complex heterochronic changes including shifts of developmental events between embryonic and pupal stages. Further, we provide, to our knowledge, the first example of sequence heterochrony in brain development, where certain developmental steps changed their position within the ontogenetic progression. We show that through this sequence heterochrony, an immature developmental stage of the central complex gains functionality in Tribolium larvae.
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  • Journal Article

    Quantitative Hormone Signaling Output Analyses of Arabidopsis thaliana Interactions With Virulent and Avirulent Hyaloperonospora arabidopsidis Isolates at Single-Cell Resolution 

    Ghareeb, Hassan; El-Sayed, Mohamed; Pound, Michael; Tetyuk, Olena; Hanika, Katharina; Herrfurth, Cornelia; Feussner, Ivo; Lipka, Volker
    Frontiers in Plant Science 2020; 11 p.1-15: Art. 603693
    The phytohormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) are central regulators of biotic and abiotic stress responses in Arabidopsis thaliana. Here, we generated modular fluorescent protein-based reporter lines termed COLORFUL-PR1pro, -VSP2pro, and -PDF1.2apro. These feature hormone-controlled nucleus-targeted transcriptional output sensors and the simultaneous constitutive expression of spectrally separated nuclear reference and plasma membrane-localized reporters. This set-up allowed the study of cell-type specific hormone activities, cellular viability and microbial invasion. Moreover, we developed a software-supported high-throughput confocal microscopy imaging protocol for output quantification to resolve the spatio-temporal dynamics of respective hormonal signaling activities at single-cell resolution. Proof-of-principle analyses in A. thaliana leaves revealed distinguished hormone sensitivities in mesophyll, epidermal pavement and stomatal guard cells, suggesting cell type-specific regulatory protein activities. In plant-microbe interaction studies, we found that virulent and avirulent Hyaloperonospora arabidopsidis (Hpa) isolates exhibit different invasion dynamics and induce spatio-temporally distinct hormonal activity signatures. On the cellular level, these hormone-controlled reporter signatures demarcate the nascent sites of Hpa entry and progression, and highlight initiation, transduction and local containment of immune signals.
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  • Journal Article

    The High Osmolarity Glycerol Mitogen-Activated Protein Kinase regulates glucose catabolite repression in filamentous fungi 

    de Assis, Leandro José; Silva, Lilian Pereira; Liu, Li; Schmitt, Kerstin; Valerius, Oliver; Braus, Gerhard H.; Ries, Laure Nicolas Annick; Goldman, Gustavo Henrique
    PLOS Genetics 2020; 16(8) p.1-27: Art. e1008996
    The utilization of different carbon sources in filamentous fungi underlies a complex regulatory network governed by signaling events of different protein kinase pathways, including the high osmolarity glycerol (HOG) and protein kinase A (PKA) pathways. This work unraveled cross-talk events between these pathways in governing the utilization of preferred (glucose) and non-preferred (xylan, xylose) carbon sources in the reference fungus Aspergillus nidulans. An initial screening of a library of 103 non-essential protein kinase (NPK) deletion strains identified several mitogen-activated protein kinases (MAPKs) to be important for carbon catabolite repression (CCR). We selected the MAPKs Ste7, MpkB, and PbsA for further characterization and show that they are pivotal for HOG pathway activation, PKA activity, CCR via regulation of CreA cellular localization and protein accumulation, as well as for hydrolytic enzyme secretion. Protein-protein interaction studies show that Ste7, MpkB, and PbsA are part of the same protein complex that regulates CreA cellular localization in the presence of xylan and that this complex dissociates upon the addition of glucose, thus allowing CCR to proceed. Glycogen synthase kinase (GSK) A was also identified as part of this protein complex and shown to potentially phosphorylate two serine residues of the HOG MAPKK PbsA. This work shows that carbon source utilization is subject to cross-talk regulation by protein kinases of different signaling pathways. Furthermore, this study provides a model where the correct integration of PKA, HOG, and GSK signaling events are required for the utilization of different carbon sources.
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  • Journal Article

    Protists and collembolans alter microbial community composition, C dynamics and soil aggregation in simplified consumer–prey systems 

    Erktan, Amandine; Rillig, Matthias C.; Carminati, Andrea; Jousset, Alexandre; Scheu, Stefan
    Biogeosciences 2020; 17(20) p.4961-4980
    Microbes play an essential role in soil functioning including biogeochemical cycling and soil aggregate formation. Yet, a major challenge is to link microbes to higher trophic levels and assess consequences for soil functioning. Here, we aimed to assess how microbial consumers modify microbial community composition (PLFA markers), as well as C dynamics (microbial C use, SOC concentration and CO$_2$ emission) and soil aggregation. We rebuilt two simplified soil consumer–prey systems: a bacterial-based system comprising amoebae (Acanthamoeba castellanii) feeding on a microbial community dominated by the free-living bacterium Pseudomonas fluorescens and a fungal-based system comprising collembolans (Heteromurus nitidus) grazing on a microbial community dominated by the saprotrophic fungus Chaetomium globosum. The amoeba A. castellanii did not affect microbial biomass and composition, but it enhanced the formation of soil aggregates and tended to reduce their stability. Presumably, the dominance of P. fluorescens, able to produce antibiotic toxins in response to the attack by A. castellanii, was the main cause of the unchanged microbial community composition, and the release of bacterial extracellular compounds, such as long-chained polymeric substances or proteases, in reaction to predation was responsible for the changes in soil aggregation as a side effect. In the fungal system, collembolans significantly modified microbial community composition via consumptive and non-consumptive effects including the transport of microbes on the body surface. As expected, fungal biomass promoted soil aggregation and was reduced in the presence of H. nitidus. Remarkably, we also found an unexpected contribution of changes in bacterial community composition to soil aggregation. In both the bacterial and fungal systems, bacterial and fungal communities mainly consumed C from soil organic matter (rather than the litter added). Increased fungal biomass was associated with an increased capture of C from added litter, and the presence of collembolans levelled off this effect. Neither amoebae nor collembolans altered SOC concentrations and CO$_2$ production. Overall, the results demonstrated that trophic interactions are important for achieving a mechanistic understanding of biological contributions to soil aggregation and may occur without major changes in C dynamics and with or without changes in the composition of the microbial community.
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  • Journal Article

    Selection markers for transformation of the sequenced reference monokaryon Okayama 7/#130 and homokaryon AmutBmut of Coprinopsis cinerea 

    Dörnte, Bastian; Peng, Can; Fang, Zemin; Kamran, Aysha; Yulvizar, Cut; Kües, Ursula
    Fungal Biology and Biotechnology. 2020 Oct 12;7(1):15
    Abstract Background Two reference strains have been sequenced from the mushroom Coprinopsis cinerea, monokaryon Okayama 7/#130 (OK130) and the self-compatible homokaryon AmutBmut. An adenine-auxotrophy in OK130 (ade8-1) and a para-aminobenzoic acid (PABA)-auxotrophy in AmutBmut (pab1-1) offer selection markers for transformations. Of these two strains, homokaryon AmutBmut had been transformed before to PABA-prototrophy and with the bacterial hygromycin resistance marker hph, respectively. Results Gene ade8 encodes a bifunctional enzyme with an N-terminal glycinamide ribonucleotide synthase (GARS) and a C-terminal aminoimidazole ribonucleotide synthase (AIRS) domain required for steps 2 and 5 in the de novo biosynthesis of purines, respectively. In OK130, a missense mutation in ade8-1 rendered residue N231 for ribose recognition by the A loop of the GARS domain into D231. The new ade8+ vector pCcAde8 complements the auxotrophy of OK130 in transformations. Transformation rates with pCcAde8 in single-vector and co-transformations with ade8+-selection were similarly high, unlike for trp1+ plasmids which exhibit suicidal feedback-effects in single-vector transformations with complementation of tryptophan synthase defects. As various other plasmids, unselected pCcAde8 helped in co-transformations of trp1 strains with a trp1+-selection vector to overcome suicidal effects by transferred trp1+. Co-transformation rates of pCcAde8 in OK130 under adenine selection with nuclear integration of unselected DNA were as high as 80% of clones. Co-transformation rates of expressed genes reached 26–42% for various laccase genes and up to 67% with lcc9 silencing vectors. The bacterial gene hph can also be used as another, albeit less efficient, selection marker for OK130 transformants, but with similarly high co-transformation rates. We further show that the pab1-1 defect in AmutBmut is due to a missense mutation which changed the conserved PIKGT motif for chorismate binding in the C-terminal PabB domain to PIEGT in the mutated 4-amino-4-deoxychorismate synthase. Conclusions ade8-1 and pab1-1 auxotrophic defects in C. cinerea reference strains OK130 and AmutBmut for complementation in transformation are described. pCcAde8 is a new transformation vector useful for selection in single and co-transformations of the sequenced monokaryon OK130 which was transformed for the first time. The bacterial gene hph can also be used as an additional selection marker in OK130, making in combination with ade8+ successive rounds of transformation possible.
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  • Journal Article

    Mycoparasite Hypomyces odoratus infests Agaricus xanthodermus fruiting bodies in nature 

    Lakkireddy, Kiran; Khonsuntia, Weeradej; Kües, Ursula
    AMB Express. 2020 Aug 13;10(1):141
    Abstract Mycopathogens are serious threats to the crops in commercial mushroom cultivations. In contrast, little is yet known on their occurrence and behaviour in nature. Cobweb infections by a conidiogenous Cladobotryum-type fungus identified by morphology and ITS sequences as Hypomyces odoratus were observed in the year 2015 on primordia and young and mature fruiting bodies of Agaricus xanthodermus in the wild. Progress in development and morphologies of fruiting bodies were affected by the infections. Infested structures aged and decayed prematurely. The mycoparasites tended by mycelial growth from the surroundings to infect healthy fungal structures. They entered from the base of the stipes to grow upwards and eventually also onto lamellae and caps. Isolated H. odoratus strains from a diseased standing mushroom, from a decaying overturned mushroom stipe and from rotting plant material infected mushrooms of different species of the genus Agaricus while Pleurotus ostreatus fruiting bodies were largely resistant. Growing and grown A. xanthodermus and P. ostreatus mycelium showed degrees of resistance against the mycopathogen, in contrast to mycelium of Coprinopsis cinerea. Mycelial morphological characteristics (colonies, conidiophores and conidia, chlamydospores, microsclerotia, pulvinate stroma) and variations of five different H. odoratus isolates are presented. In pH-dependent manner, H. odoratus strains stained growth media by pigment production yellow (acidic pH range) or pinkish-red (neutral to slightly alkaline pH range).
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  • Journal Article

    The integrated stress response induces R-loops and hinders replication fork progression 

    Choo, Josephine Ann Mun Yee; Schlösser, Denise; Manzini, Valentina; Magerhans, Anna; Dobbelstein, Matthias
    Cell Death & Disease 2020; 11(7) p.1-16: Art. 538
    The integrated stress response (ISR) allows cells to rapidly shutdown most of their protein synthesis in response to protein misfolding, amino acid deficiency, or virus infection. These stresses trigger the phosphorylation of the translation initiation factor eIF2alpha, which prevents the initiation of translation. Here we show that triggering the ISR drastically reduces the progression of DNA replication forks within 1 h, thus flanking the shutdown of protein synthesis with immediate inhibition of DNA synthesis. DNA replication is restored by compounds that inhibit eIF2alpha kinases or re-activate eIF2alpha. Mechanistically, the translational shutdown blocks histone synthesis, promoting the formation of DNA:RNA hybrids (R-loops), which interfere with DNA replication. R-loops accumulate upon histone depletion. Conversely, histone overexpression or R-loop removal by RNaseH1 each restores DNA replication in the context of ISR and histone depletion. In conclusion, the ISR rapidly stalls DNA synthesis through histone deficiency and R-loop formation. We propose that this shutdown mechanism prevents potentially detrimental DNA replication in the face of cellular stresses.
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  • Journal Article

    Probing the Environment of Emerin by Enhanced Ascorbate Peroxidase 2 (APEX2)-Mediated Proximity Labeling 

    Müller, Marret; James, Christina; Lenz, Christof; Urlaub, Henning; Kehlenbach, Ralph H.
    Cells 2020; 9(3) p.1-18: Art. 605
    Emerin is one of the best characterized proteins of the inner nuclear membrane, but can also occur at the level of the endoplasmic reticulum. We now use enhanced ascorbate peroxidase 2 (APEX2) to probe the environment of emerin. APEX2 can be used as a genetic tag that produces short-lived yet highly reactive biotin species, allowing the modification of proteins that interact with or are in very close proximity to the tagged protein. Biotinylated proteins can be isolated using immobilized streptavidin and analyzed by mass spectrometry. As an alternative to the standard approach with a genetic fusion of APEX2 to emerin, we also used RAPIDS (rapamycin- and APEX-dependent identification of proteins by SILAC), a method with improved specificity, where the peroxidase interacts with the protein of interest (i.e., emerin) only upon addition of rapamycin to the cells. We compare these di erent approaches, which, together, identify well-known interaction partners of emerin like lamin A and the lamina associated polypeptide 1 (LAP1), as well as novel proximity partners.
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  • Journal Article

    Dbp5/DDX19 between Translational Readthrough and Nonsense Mediated Decay 

    Beißel, Christian; Grosse, Sebastian; Krebber, Heike
    International Journal of Molecular Sciences 2020; 21(3) p.1-13: Art. 1085
    The DEAD-box protein Dbp5 (human DDX19) remodels RNA-protein complexes. Dbp5 functions in ribonucleoprotein export and translation termination. Termination occurs, when the ribosome has reached a stop codon through the Dbp5 mediated delivery of the eukaryotic termination factor eRF1. eRF1 contacts eRF3 upon dissociation of Dbp5, resulting in polypeptide chain release and subsequent ribosomal subunit splitting. Mutations in DBP5 lead to stop codon readthrough, because the eRF1 and eRF3 interaction is not controlled and occurs prematurely. This identifies Dbp5/DDX19 as a possible potent drug target for nonsense suppression therapy. Neurodegenerative diseases and cancer are caused in many cases by the loss of a gene product, because its mRNA contained a premature termination codon (PTC) and is thus eliminated through the nonsense mediated decay (NMD) pathway, which is described in the second half of this review. We discuss translation termination andNMDin the light of Dbp5/DDX19 and subsequently speculate on reducing Dbp5/DDX19 activity to allow readthrough of the PTC and production of a full-length protein to detract the RNA from NMD as a possible treatment for diseases.
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  • Journal Article

    The number of k-mer matches between two DNA sequences as a function of k and applications to estimate phylogenetic distances 

    Röhling, Sophie; Linne, Alexander; Schellhorn, Jendrik; Hosseini, Morteza; Dencker, Thomas; Morgenstern, Burkhard
    PLOS ONE 2020; 15(2) p.1-18: Art. e0228070
    We study the number $N_k$ of length-k word matches between pairs of evolutionarily related DNA sequences, as a function of k. We show that the Jukes-Cantor distance between two genome sequences—i.e. the number of substitutions per site that occurred since they evolved from their last common ancestor—can be estimated from the slope of a function $F$ that depends on $N_k$ and that is affine-linear within a certain range of $k$. Integers kmin and $k_{max}$ can be calculated depending on the length of the input sequences, such that the slope of $F$ in the relevant range can be estimated from the values $F(k_{min})$ and $F(k_{max})$. This approach can be generalized to so-called Spaced-word Matches (SpaM), where mismatches are allowed at positions specified by a user-defined binary pattern. Based on these theoretical results, we implemented a prototype software program for alignment-free sequence comparison called Slope-SpaM. Test runs on real and simulated sequence data show that Slope-SpaM can accurately estimate phylogenetic distances for distances up to around 0.5 substitutions per position. The statistical stability of our results is improved if spaced words are used instead of contiguous words. Unlike previous alignment-free methods that are based on the number of (spaced) word matches, Slope-SpaM produces accurate results, even if sequences share only local homologies.
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  • Journal Article

    Gene content evolution in the arthropods 

    Thomas, Gregg W. C.; Dohmen, Elias; Hughes, Daniel S. T.; Murali, Shwetha C.; Poelchau, Monica; Glastad, Karl; Anstead, Clare A.; Ayoub, Nadia A; Batterham, Phillip; Bellair, Michelle; et al.
    Binford, Greta J.Chao, HsuChen, Yolanda H.Childers, ChristopherDinh, HuyenDoddapaneni, Harsha V.Duan, Jian J.Dugan, ShannonEsposito, Lauren A.Friedrich, MarkusGarb, JessicaGasser, Robin B.Goodisman, Michael A. D.Gundersen-Rindal, Dawn E.Han, YiHandler, Alfred M.Hatakeyama, MasatsuguHering, LarsHunter, Wayne B.Ioannidis, PanagiotisJayaseelan, Joy C.Kalra, DivyaKhila, AbderrahmanKorhonen, Pasi K.Lee, Carol E.Lee, Sandra L.Li, YiyuanLindsey, Amelia R. I.Mayer, GeorgMcGregor, Alistair P.McKenna, Duane D.Misof, BernhardMunidasa, MalaMunoz-Torres, MonicaMuzny, Donna M.Niehuis, OliverOsuji-Lacy, NkechinyerePalli, Subba R.Panfilio, Kristen A.Pechmann, MatthiasPerry, TrentPeters, Ralph S.Poynton, Helen C.Prpic, Nikola-MichaelQu, JiaxinRotenberg, DorithSchal, CobySchoville, Sean D.Scully, Erin D.Skinner, EvetteSloan, Daniel B.Stouthamer, RichardStrand, Michael R.Szucsich, Nikolaus U.Wijeratne, AselaYoung, Neil D.Zattara, Eduardo E.Benoit, Joshua B.Zdobnov, Evgeny M.Pfrender, Michael E.Hackett, Kevin J.Werren, John H.Worley, Kim C.Gibbs, Richard A.Chipman, Ariel D.Waterhouse, Robert M.Bornberg-Bauer, ErichHahn, Matthew W.Richards, Stephen
    Genome Biology. 2020 Jan 23;21(1):15
    Background Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. Results Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. Conclusions These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity.
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  • Journal Article

    Transcriptome of pleuropodia from locust embryos supports that these organs produce enzymes enabling the larva to hatch 

    Konopová, Barbora; Buchberger, Elisa; Crisp, Alastair
    Frontiers in Zoology. 2020 Jan 16;17(1):4
    Background Pleuropodia are limb-derived glandular organs that transiently appear on the first abdominal segment in embryos of insects from majority of “orders”. They are missing in the genetic model Drosophila and little is known about them. Experiments carried out on orthopteran insects 80 years ago indicated that the pleuropodia secrete a “hatching enzyme” that digests the serosal cuticle to enable the larva to hatch, but evidence by state-of-the-art molecular methods is missing. Results We used high-throughput RNA-sequencing to identify the genes expressed in the pleuropodia of the locust Schistocerca gregaria (Orthoptera). First, using transmission electron microscopy we studied the development of the pleuropodia during 11 stages of the locust embryogenesis. We show that the glandular cells differentiate and start secreting just before the definitive dorsal closure of the embryo and the secretion granules outside the cells become more abundant prior to hatching. Next, we generated a comprehensive embryonic reference transcriptome for the locust and used it to study genome wide gene expression across ten morphologicaly defined stages of the pleuropodia. We show that when the pleuropodia have morphological markers of functional organs and produce secretion, they are primarily enriched in transcripts associated with transport functions. They express genes encoding enzymes capable of digesting cuticular protein and chitin. These include the potent cuticulo-lytic Chitinase 5, whose transcript rises just before hatching. Unexpected finding was the enrichment in transcripts for immunity-related enzymes. This indicates that the pleuropodia are equipped with epithelial immunity similarly as barrier epithelia in postembryonic stages. Conclusions These data provide transcriptomic support for the historic hypothesis that pleuropodia produce cuticle-degrading enzymes and function in hatching. They may also have other functions, such as facilitation of embryonic immune defense. By the genes that they express the pleuropodia are specialized embryonic organs and apparently an important though neglected part of insect physiology.
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  • Journal Article

    Enhanced genome assembly and a new official gene set for Tribolium castaneum 

    Herndon, Nicolae; Shelton, Jennifer; Gerischer, Lizzy; Ioannidis, Panos; Ninova, Maria; Dönitz, Jürgen; Waterhouse, Robert M; Liang, Chun; Damm, Carsten; Siemanowski, Janna; et al.
    Kitzmann, PeterUlrich, JuliaDippel, StefanOberhofer, GeorgHu, YonggangSchwirz, JonasSchacht, MagdalenaLehmann, SabrinaMontino, AlicePosnien, NicoGurska, DanielaHorn, ThorstenSeibert, JanVargas Jentzsch, Iris MPanfilio, Kristen ALi, JianweiWimmer, Ernst AStappert, DominikRoth, SiegfriedSchröder, ReinhardPark, YoonseongSchoppmeier, MichaelChung, Ho-RyunKlingler, MartinKittelmann, SebastianFriedrich, MarkusChen, RuiAltincicek, BoranVilcinskas, AndreasZdobnov, EvgenyGriffiths-Jones, SamRonshaugen, MatthewStanke, MarioBrown, Sue JBucher, Gregor
    BMC Genomics. 2020 Jan 14;21(1):47
    Background The red flour beetle Tribolium castaneum has emerged as an important model organism for the study of gene function in development and physiology, for ecological and evolutionary genomics, for pest control and a plethora of other topics. RNA interference (RNAi), transgenesis and genome editing are well established and the resources for genome-wide RNAi screening have become available in this model. All these techniques depend on a high quality genome assembly and precise gene models. However, the first version of the genome assembly was generated by Sanger sequencing, and with a small set of RNA sequence data limiting annotation quality. Results Here, we present an improved genome assembly (Tcas5.2) and an enhanced genome annotation resulting in a new official gene set (OGS3) for Tribolium castaneum, which significantly increase the quality of the genomic resources. By adding large-distance jumping library DNA sequencing to join scaffolds and fill small gaps, the gaps in the genome assembly were reduced and the N50 increased to 4753kbp. The precision of the gene models was enhanced by the use of a large body of RNA-Seq reads of different life history stages and tissue types, leading to the discovery of 1452 novel gene sequences. We also added new features such as alternative splicing, well defined UTRs and microRNA target predictions. For quality control, 399 gene models were evaluated by manual inspection. The current gene set was submitted to Genbank and accepted as a RefSeq genome by NCBI. Conclusions The new genome assembly (Tcas5.2) and the official gene set (OGS3) provide enhanced genomic resources for genetic work in Tribolium castaneum. The much improved information on transcription start sites supports transgenic and gene editing approaches. Further, novel types of information such as splice variants and microRNA target genes open additional possibilities for analysis.
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  • Journal Article

    Disruption of Arabidopsis neutral ceramidases 1 and 2 results in specific sphingolipid imbalances triggering different phytohormone‐dependent plant cell death programmes 

    Zienkiewicz, Agnieszka; Gömann, Jasmin; König, Stefanie; Herrfurth, Cornelia; Liu, Yi‐Tse; Meldau, Dorothea; Feussner, Ivo
    New Phytologist p.1-19
    Sphingolipids act as regulators of programmed cell death (PCD) and the plant defence response. The homeostasis between long-chain base (LCB) and ceramide (Cer) seems to play an important role in executions of PCD. Therefore, deciphering the role of neutral ceramidases (NCER) is crucial to identify the sphingolipid compounds that trigger and execute PCD. We performed comprehensive sphingolipid and phytohormone analyses of Arabidopsis ncer mutants, combined with gene expression profiling and microscopic analyses. While ncer1 exhibited early leaf senescence (developmentally controlled PCD - dPCD) and an increase in hydroxyceramides, ncer2 showed spontaneous cell death (pathogen-triggered PCD-like - pPCD) accompanied by an increase in LCB t18:0 at 35 d, respectively. Loss of NCER1 function resulted in accumulation of jasmonoyl-isoleucine (JA-Ile) in the leaves, whereas disruption of NCER2 was accompanied by higher levels of salicylic acid (SA) and increased sensitivity to Fumonisin B1 (FB1 ). All mutants were also found to activate plant defence pathways. These data strongly suggest that NCER1 hydrolyses ceramides whereas NCER2 functions as a ceramide synthase. Our results reveal an important role of NCER in the regulation of both dPCD and pPCD via a tight connection between the phytohormone and sphingolipid levels in these two processes.
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  • Journal Article

    Conditional gene expression reveals stage‐specific functions of the unfolded protein response in the Ustilago maydis– maize pathosystem 

    Schmitz, Lara; Kronstad, James W.; Heimel, Kai
    Molecular Plant Pathology
    Ustilago maydis is a model organism for the study of biotrophic plant-pathogen interactions. The sexual and pathogenic development of the fungus are tightly connected since fusion of compatible haploid sporidia is prerequisite for infection of the host plant, maize (Zea mays). After plant penetration, the unfolded protein response (UPR) is activated and required for biotrophic growth. The UPR is continuously active throughout all stages of pathogenic development in planta. However, since development of UPR deletion mutants stops directly after plant penetration, the role of an active UPR at later stages of development remained to be determined. Here, we establish a gene expression system for U. maydis that uses endogenous, conditionally active promoters to either induce or repress expression of a gene of interest during different stages of plant infection. Integration of the expression constructs into the native genomic locus and removal of resistance cassettes were required to obtain a wild-type-like expression pattern. This indicates that genomic localization and chromatin structure are important for correct promoter activity and gene expression. By conditional expression of the central UPR regulator, Cib1, in U. maydis, we show that a functional UPR is required for continuous plant defence suppression after host infection and that U. maydis relies on a robust control system to prevent deleterious UPR hyperactivation.
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  • Journal Article

    A key role for foxQ2 in anterior head and central brain patterning in insects 

    Kitzmann, Peter; Weißkopf, Matthias; Schacht, Magdalena Ines; Bucher, Gregor
    Development 2017; 144(16) p.2969-2981
    Anterior patterning of animals is based on a set of highly conserved transcription factors but the interactions within the protostome anterior gene regulatory network (aGRN) remain enigmatic. Here, we identify the red flour beetle Tribolium castaneum ortholog of foxQ2 (Tc-foxQ2) as a novel upstream component of the aGRN. It is required for the development of the labrum and higher order brain structures, namely the central complex and the mushroom bodies. We reveal Tc-foxQ2 interactions by RNAi and heat shock-mediated misexpression. Surprisingly, Tc-foxQ2 and Tc-six3 mutually activate each other, forming a novel regulatory module at the top of the aGRN. Comparisons of our results with those of sea urchins and cnidarians suggest that foxQ2 has acquired more upstream functions in the aGRN during protostome evolution. Our findings expand the knowledge on foxQ2 gene function to include essential roles in epidermal development and central brain patterning.
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  • Journal Article

    Specific expression and function of the Six3 optix in Drosophila serially homologous organs 

    Al Khatib, Amer; Siomava, Natalia; Iannini, Antonella; Posnien, Nico; Casares, Fernando
    Biology Open 2017; 6(8) p.1155-1164
    Organ size and pattern results from the integration of two positional information systems. One global information system, encoded by the Hox genes, links organ type with position along the main body axis. Within specific organs, local information is conveyed by signaling molecules that regulate organ growth and pattern. The mesothoracic (T2) wing and the metathoracic (T3) haltere of Drosophila represent a paradigmatic example of this coordination. The Hox gene Ultrabithorax (Ubx), expressed in the developing T3, selects haltere identity by, among other processes, modulating the production and signaling efficiency of Dpp, a BMP2-like molecule that acts as a major regulator of size and pattern. However, the mechanisms of the Hox-signal integration in this well-studied system are incomplete. Here, we have investigated this issue by studying the expression and function of the Six3 transcription factor optix during Drosophila wing and haltere development. We find that in both organs, Dpp defines the expression domain of optix through repression, and that the specific position of this domain in wing and haltere seems to reflect the differential signaling profile among these organs. We show that optix expression in wing and haltere primordia is conserved beyond Drosophila in other higher diptera. In Drosophila, optix is necessary for the growth of wing and haltere. In the wing, optix is required for the growth of the most anterior/proximal region (the 'marginal cell') and for the correct formation of sensory structures along the proximal anterior wing margin; the halteres of optix mutants are also significantly reduced. In addition, in the haltere, optix is necessary for the suppression of sensory bristles.
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  • Journal Article

    An ancestral apical brain region contributes to the central complex under the control of foxQ2 in the beetle Tribolium 

    He, Bicheng; Buescher, Marita; Farnworth, Max Stephen; Strobl, Frederic; Stelzer, Ernst HK; Koniszewski, Nikolaus DB; Muehlen, Dominik; Bucher, Gregor
    eLife 2019; 8: Art. e49065
    The genetic control of anterior brain development is highly conserved throughout animals. For instance, a conserved anterior gene regulatory network specifies the ancestral neuroendocrine center of animals and the apical organ of marine organisms. However, its contribution to the brain in non-marine animals has remained elusive. Here, we study the function of the Tc-foxQ2 forkhead transcription factor, a key regulator of the anterior gene regulatory network of insects. We characterized four distinct types of Tc-foxQ2 positive neural progenitor cells based on differential co-expression with Tc-six3/optix, Tc-six4, Tc-chx/vsx, Tc-nkx2.1/scro, Tc-ey, Tc-rx and Tc-fez1. An enhancer trap line built by genome editing marked Tc-foxQ2 positive neurons, which projected through the primary brain commissure and later through a subset of commissural fascicles. Eventually, they contributed to the central complex. Strikingly, in Tc-foxQ2 RNAi knock-down embryos the primary brain commissure did not split and subsequent development of midline brain structures stalled. Our work establishes foxQ2 as a key regulator of brain midline structures, which distinguish the protocerebrum from segmental ganglia. Unexpectedly, our data suggest that the central complex evolved by integrating neural cells from an ancestral anterior neuroendocrine center.
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  • Journal Article

    Improvement and use of CRISPR/Cas9 to engineer a sperm-marking strain for the invasive fruit pest Drosophila suzukii 

    Ahmed, Hassan M. M.; Hildebrand, Luisa; Wimmer, Ernst A.
    BMC Biotechnology. 2019 Dec 05;19(1):85
    Background The invasive fruit pest Drosophila suzukii was reported for the first time in Europe and the USA in 2008 and has spread since then. The adoption of type II clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) as a tool for genome manipulation provides new ways to develop novel biotechnologically-based pest control approaches. Stage or tissue-specifically expressed genes are of particular importance in the field of insect biotechnology. The enhancer/promoter of the spermatogenesis-specific beta-2-tubulin (β2t) gene was used to drive the expression of fluorescent proteins or effector molecules in testes of agricultural pests and disease vectors for sexing, monitoring, and reproductive biology studies. Here, we demonstrate an improvement to CRISPR/Cas-based genome editing in D. suzukii and establish a sperm-marking system. Results To improve genome editing, we isolated and tested the D. suzukii endogenous promoters of the small nuclear RNA gene U6 to drive the expression of a guide RNA and the Ds heat shock protein 70 promoter to express Cas9. For comparison, we used recombinant Cas9 protein and in vitro transcribed gRNA as a preformed ribonucleoprotein. We demonstrate the homology-dependent repair (HDR)-based genome editing efficiency by applying a previously established transgenic line that expresses DsRed ubiquitously as a target platform. In addition, we isolated the Ds_β2t gene and used its promoter to drive the expression of a red fluorescence protein in the sperm. A transgenic sperm-marking strain was then established by the improved HDR-based genome editing. Conclusion The deployment of the endogenous promoters of the D. suzukii U6 and hsp70 genes to drive the expression of gRNA and Cas9, respectively, enabled the effective application of helper plasmid co-injections instead of preformed ribonucleoproteins used in previous reports for HDR-based genome editing. The sperm-marking system should help to monitor the success of pest control campaigns in the context of the Sterile Insect Technique and provides a tool for basic research in reproductive biology of this invasive pest. Furthermore, the promoter of the β2t gene can be used in developing novel transgenic pest control approaches and the CRISPR/Cas9 system as an additional tool for the modification of previously established transgenes.
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  • Journal Article

    Genome sequencing of evolved aspergilli populations reveals robust genomes, transversions in A. flavus, and sexual aberrancy in non-homologous end-joining mutants 

    Álvarez-Escribano, Isidro; Sasse, Christoph; Bok, Jin W; Na, Hyunsoo; Amirebrahimi, Mojgan; Lipzen, Anna; Schackwitz, Wendy; Martin, Joel; Barry, Kerrie; Gutiérrez, Gabriel; et al.
    Cea-Sánchez, SaraMarcos, Ana TGrigoriev, Igor VKeller, Nancy PBraus, Gerhard HCánovas, David
    BMC Biology. 2019 Nov 11;17(1):88
    Abstract Background Aspergillus spp. comprises a very diverse group of lower eukaryotes with a high relevance for industrial applications and clinical implications. These multinucleate species are often cultured for many generations in the laboratory, which can unknowingly propagate hidden genetic mutations. To assess the likelihood of such events, we studied the genome stability of aspergilli by using a combination of mutation accumulation (MA) lines and whole genome sequencing. Results We sequenced the whole genomes of 30 asexual and 10 sexual MA lines of three Aspergillus species (A. flavus, A. fumigatus and A. nidulans) and estimated that each MA line accumulated mutations for over 4000 mitoses during asexual cycles. We estimated mutation rates of 4.2 × 10−11 (A. flavus), 1.1 × 10−11 (A. fumigatus) and 4.1 × 10−11 (A. nidulans) per site per mitosis, suggesting that the genomes are very robust. Unexpectedly, we found a very high rate of GC → TA transversions only in A. flavus. In parallel, 30 asexual lines of the non-homologous end-joining (NHEJ) mutants of the three species were also allowed to accumulate mutations for the same number of mitoses. Sequencing of these NHEJ MA lines gave an estimated mutation rate of 5.1 × 10−11 (A. flavus), 2.2 × 10−11 (A. fumigatus) and 4.5 × 10−11 (A. nidulans) per base per mitosis, which is slightly higher than in the wild-type strains and some ~ 5–6 times lower than in the yeasts. Additionally, in A. nidulans, we found a NHEJ-dependent interference of the sexual cycle that is independent of the accumulation of mutations. Conclusions We present for the first time direct counts of the mutation rate of filamentous fungal species and find that Aspergillus genomes are very robust. Deletion of the NHEJ machinery results in a slight increase in the mutation rate, but at a rate we suggest is still safe to use for biotechnology purposes. Unexpectedly, we found GC→TA transversions predominated only in the species A. flavus, which could be generated by the hepatocarcinogen secondary metabolite aflatoxin. Lastly, a strong effect of the NHEJ mutation in self-crossing was observed and an increase in the mutations of the asexual lines was quantified.
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