Biology subjects

Grabe, V.

Publications and source records attributed to Grabe, V..

13 recordsLinked to original sources

bioRxiv2026

An auxiliary protein tunes reductase activity in alkaloid biosynthesis

Monoterpene indole alkaloids encompass a diverse class of plant natural products. Many of these valuable compounds, including the anticancer medicines vinblastine and vincristine (Catharanthus roseus) and the antiaddiction treatment ibogaine (Tabernanthe iboga) utilize a common biosynthetic intermediate, 19E-geissoschizine, which is produced by the medium-chain dehydrogenase/reductase geissoschizine synthase (GS). Herein we report the discovery of a non-catalytic auxiliary protein (facilitator of geissoschizine synthase, FoGS) that improves formation of 19E-geissoschizine by acting in combination with GS. The discovery of a FoGS orthologue that works with GS to produce 19Z-geissoschizine shows how this protein also controls the stereochemistry of the product. We demonstrate that FoGS and GS interact to form a stable heterodimer, and show through mutagenesis that FoGS likely modulates the structure of the GS active site. Microscopy studies suggest that FoGS also changes the subcellular localization of GS. The discovery of FoGS will enable efforts to heterologously reconstitute commercially important geissoschizine-derived monoterpene indole alkaloids, and moreover, highlights how metabolic pathways utilize proteins that are not essential for production of the products, but nevertheless enhance the efficiency and specificity of the catalytic biosynthetic pathway components.

biochemistry↗

bioRxiv2026

The spruce bark beetle Ips typographus transmits mutualistic fungi in mandibular mycetangia

Insects associated with mutualistic microbes often possess structures specialized for microbial transport that ensure the maintenance of these symbioses. Called mycetangia, these structures have evolved in numerous bark beetle species facilitating fungal transport to new host trees. The Eurasian spruce bark beetle Ips typographus is associated with several filamentous ascomycetes that may provide beetles with nutrition or help overcome tree defenses. I. typographus has been believed to vector its fungal symbionts mostly on the exoskeleton, but exact mechanisms of fungal transmission are unknown. Here, we report the discovery of a mandibular mycetangium in I. typographus that enables the transmission of symbiotic fungi. Extensive fungal isolation from I. typographus heads suggested the presence of a mycetangium while micro-computed tomography and histological analyses revealed a mycetangium close to the mandibles. Strikingly, we identified these fungus-carrying structures in both sexes of I. typographus and in the congeneric species I. acuminatus, and I. duplicatus, although mandibular mycetangia have been thought to be rare in Ips bark beetles. Moreover, mycetangia in male beetles in general were hardly reported in bark beetles before. The occurrence of mycetangia in Ips species highlights the important role mutualistic fungi play in the natural history of these bark beetles.

ecology↗

bioRxiv2025

Conserved early steps of stemmadenine biosynthesis

Stemmadenine acetate is a pivotal intermediate in the production of pharmacologically active monoterpene indole alkaloids. Here, we identify orthologs of stemmadenine acetate pathway genes (SGD, GS, GO, Redox1, Redox2, SAT) from Tabernanthe iboga. We characterize these enzymes in vitro, and additionally, we reconstitute stemmadenine acetate biosynthesis in Nicotiana benthamiana, comparing the formation of intermediates and shunt products that are produced when previously characterized orthologs from the related plant Catharanthus roseus are used. Ortholog pairs are catalytically indistinguishable, except in the case of GS. Surprisingly, the T. iboga ortholog catalyzes formation of an alternate stereoisomer 19Z-geissoschizine, seeding a low-flux Z-series in heterologous reconstitution systems in vitro and in planta. We additionally characterize the major shunt products that arose during reconstitution of stemmadenine acetate biosynthesis. We show that the substrate promiscuity of Redox2 results in formation of the shunt products 16(R/S)-isositsirikines, hampering pathway flux and yields. Additionally, we show that stemmadenine can be oxidized by endogenous N. benthamiana enzymes, leading to the shunt product condylocarpine. Nevertheless, we could produce stemmadenine at a 6 mg yield from 19E-geissoschizine by heterologous expression in N. benthamiana. Overall, we highlight the prospects for milligram production of important biosynthetic intermediates in N. benthamiana.

biochemistry↗

bioRxiv2025

Maladaptive aphid-induced transgenerational plasticity is overcome in nature

Inherited stress responses are widely assumed to be adaptive for plants by preparing offspring for renewed attack. To date, it remains unclear whether and under which conditions these responses may benefit the attacker rather than the host. Studying the interaction between the aphid Rhopalosiphum nymphaeae and its native host, the aquatic duckweed Spirodela polyrhiza, we show that aphids can either benefit or suffer from inherited stress responses, depending on metabolite identity and ecological context. In multigenerational clonal plant lineages maintained indoors, ancestral aphid herbivory increased aphid reproduction and reduced plant fitness under renewed attack, indicating that the net effect of inherited stress responses can favor the herbivore. However, not all inherited responses benefited the aphid: using genetic and chemical manipulations, we found that transgenerational priming of jasmonate enhanced aphid performance, whereas transgenerational priming of tyramine reduced it. Notably, tyramine--but not jasmonates--accumulated to higher levels across generations also in large mesocosms outdoors, albeit only within and not across growing seasons. Together, our results reveal that inherited responses of hosts can favor the attackers and highlight ecological context and life-cycle transitions as key determinants of the persistence, duration, and ecological consequences of inherited stress responses.

ecology↗

bioRxiv2024

Independent evolution of ipecac alkaloid biosynthesis

Ipecac alkaloids are medicinal monoterpenoid-derived tetrahydroisoquinoline alkaloids found in two distantly related plants: Carapichea ipecacuanha (Gentianales) and Alangium salviifolium (Cornales). We have elucidated ipecac alkaloid biosynthesis in both species, conclusively demonstrating that biosynthesis of the structurally complex ipecac alkaloid protoemetine has evolved independently. We show that although protoemetine biosynthesis proceeds via the same chemical logic in both species, each plant uses a distinct monoterpene precursor. Moreover, we provide evidence that both plants initiate ipecac biosynthesis by a non-enzymatic Pictet-Spengler reaction, and we elucidate the biosynthetic fate of both the 1R and 1S stereoisomers that are produced in this non-stereoselective reaction. Phylogenetic analyses clearly show independent pathway evolution through parallel and convergently evolved enzymes. This work provides insight into how nature can capitalize on highly reactive starting substrates, the manner in which multi-step pathways can arise, and also lays the foundation for metabolic engineering of these important medicinal compounds.

plant biology↗

bioRxiv2024

Highjacked by a pseudoenzyme: How eudicot plants make indole

Indole is crucial for plant defense, where it is released as a signaling volatile upon herbivore attack and also serves as a starting precursor for defensive specialized metabolites. Indole is known to be synthesized in plants from indole-3-glycerol phosphate by the enzyme indole-3-glycerol phosphate lyase. Here we report that in core eudicots, indole production for plant defense occurs via an alternative pathway. The subunit of tryptophan synthase (TSA), an enzyme of core metabolism, normally binds to tryptophan synthase {beta} subunit (TSB) to produce tryptophan. However, we show that a non-catalytic TSB paralogue (TSB-like) can highjack TSA to produce indole. The widespread occurrence of TSB-like genes in eudicots suggests that this alternative mechanism for indole formation is widespread throughout the plant kingdom.

plant biology↗

bioRxiv2024

Quantitative single cell mass spectrometry reveals the dynamics of plant natural product biosynthesis

Plants produce an extraordinary array of complex natural products (specialized metabolites). Since the biosynthetic genes that are responsible for synthesis of these molecules are often localized to rare or distinct cell types, recently developed single cell RNA-sequencing (scRNA-seq) approaches have tremendous potential to resolve these complex pathways. In contrast, detection, identification, and quantification of metabolites in single cells has remained challenging. Here, we report a robust method for single cell mass spectrometry in which we rigorously characterize and quantify the concentrations of four classes of natural products in individual cells of leaf, root, and petal of the medicinal plant Catharanthus roseus. These single cell mass spectrometry datasets reveal information about the biosynthetic processes that cannot be determined from the corresponding scRNA-seq data alone, providing a highly resolved picture of natural product biosynthesis at cell-specific resolution.

biochemistry↗

bioRxiv2023

How frequently are insects wounded in the wild? A case study using Drosophila melanogaster

O_LIWounding occurs across multicellular organisms. There is a deep understanding of infections and immune responses from lab studies, yet wounds remain relatively comparatively understudied in nature. Ecological interactions like predator attacks, intra- and inter-specific competition can lead to wounding. Furthermore, rates of wounding may vary depending on factors such as sex and geographic location, with consequences for host mobility, reproduction, and susceptibility to pathogens. C_LIO_LIWounds initiate an immune response, resulting in the deposition of the brown-black pigment melanin in insects, and they are potential entry points for pathogens. Despite the potential ecological and evolutionary implications of wounding, and the relative abundance of lab immunity studies utilising Drosophila melanogaster, wounding in the wild in this model is unstudied. Our aim, therefore, was to investigate the prevalence and examine potential causes of wounds in wild-collected D. melanogaster. C_LIO_LIFrom systematic collections of female and male flies, over three seasons and locations, we found that 31% of D. melanogaster were wounded. The abdomen was more frequently wounded than other body parts, and females were more likely to be injured particularly on the ventral abdomen, compared to males. Encapsulated parasitoid egg frequency was just under ten percent. Moreover, just under one percent of Drosophilidae species had mites attached to their body, the majority of which also caused wounds, i.e., were potentially parasitic. C_LIO_LIWounding is prevalent in D. melanogaster, and as such it is likely to exert selection pressure on host immunity for two reasons: on a rapid and efficient wound repair, and on responding to opportunistic infections. Wounds are thus expected to be important drivers of immune system evolution and to affect individual fitness and population dynamics. C_LI

ecology↗

bioRxiv2023

Experience-dependent plasticity of a highly specific olfactory circuit in Drosophila melanogaster

Drosophila melanogaster encounters a variety of odor cues signaling potentially harmful threats through-out its life, which are detected by highly specialized olfactory circuits enabling the animal to avoid them. We studied whether such crucial neuronal pathways are hard-wired or can be modulated by experience. Using long-term exposure to high concentrations of geosmin, an indicator of potentially lethal microorganisms, we demonstrate at the single-cell level that the underlying neuronal circuitry undergoes structural changes in the antennal lobe, while higher brain centers remain unaffected. In particular, second-order neurons show neurite extensions and synaptic remodeling after the exposure period, whereas olfactory sensory neurons and glia cells remain unaffected. Flies that were exposed to geosmin tolerate this innately aversive odorant in general choice and oviposition assays. We show that even a highly specific olfactory circuit is plastic and adaptable to environmental changes. HIGHLIGHTSO_LIThe highly specific geosmin circuit is modulated by experience-dependent plasticity C_LIO_LIPN dendritic extensions cause a volumetric increase of the geosmin-detecting glomerulus C_LIO_LILNs are remodeled while OSNs and glia cells remain unaffected by long-term exposure C_LIO_LIFlies adapt their behavior to an odorant signaling a potential lethal threat C_LI

neuroscience↗

bioRxiv2021

An ammonium transporter is a non-canonical olfactory receptor for ammonia

Two families of ligand-gated ion channels function as olfactory receptors in insects. Here, we show that these canonical olfactory receptors are not necessary for responses to ammonia, a key ecological odor that is attractive to many insects including disease vectors and agricultural pests. Instead, we show that a member of the ancient electrogenic ammonium transporter family, Amt, is a new type of olfactory receptor. We report two hitherto unidentified olfactory neuron populations that mediate neuronal and behavioral responses to ammonia. Their endogenous ammonia responses are Amt-dependent, and ectopic expression of either Drosophila or Anopheles Amt confers ammonia sensitivity. Amt is the first transporter known to function as an olfactory receptor in animals, and its role may be conserved across insect species.

neuroscience↗

bioRxiv2019

Mate discrimination among subspecies through a conserved olfactory pathway

Signaling mechanisms underlying the sexual isolation of species are poorly understood. Using four subspecies of Drosophila mojavensis as a model, we identify two behaviorally active male-specific pheromones. One functions as a conserved male anti-aphrodisiac in all subspecies and acts via gustation. The second induces female receptivity via olfaction exclusively in the two subspecies that produce it. Genetic analysis of the cognate receptor for the olfactory pheromone indicates an important role for this sensory pathway in promoting sexual isolation of subspecies, in collaboration with auditory signals. Surprisingly, the peripheral sensory pathway detecting this pheromone is conserved molecularly, physiologically and anatomically across subspecies. These observations imply that subspecies-specific behaviors arise from differential interpretation of the same peripheral cue, reminiscent of sexually conserved detection but dimorphic interpretation of male pheromones in D. melanogaster. Our results reveal that, during incipient speciation, pheromone production, detection and interpretation do not necessarily evolve in a coordinate manner.

neuroscience↗

bioRxiv2019

Niche partitioning as a selective pressure for the evolution of the Drosophila nervous system

The ecological and developmental selective pressures associated with evolution have shaped most animal traits, such as behavior, morphology and neurobiology. As such, the examination of phylogenetic characteristics of the nervous system can be utilized as a means to assess these traits, and thus, to evaluate the underlying selective pressures that produce evolutionary variation between species. Recent studies across a multitude of Drosophila have hypothesized the existence of a fundamental tradeoff between two primary sensory organs, the eye and the antenna. However, the identification of any potential ecological mechanisms for this observed tradeoff have not been firmly established. Our current study examines two monophyletic species within the obscura group, and asserts that despite their close relatedness and overlapping ecology, they deviate strongly in both visual and olfactory investment. Here we contend that both courtship and microhabitat preferences mirror and support the observed inverse variation in these sensory traits. Moreover, that this variation in visual and olfactory investment between closely-related species seems to provide relaxed competition, a process by which similar species can use a shared environment differently and in ways that help them both coexist. The nervous system has a unique role in evolution as it provides the functional connection between morphology, physiology, and behavior. As such, characterizing any tradeoffs between costs and benefits for the nervous system may be essential to our understanding of animal diversity, as well as vital to our understanding of the selective forces that have shaped the natural world.

evolutionary biology↗

bioRxiv2018

Silencing cuticular pigmentation genes enables RNA FISH in intact chemosensory appendages

Optical imaging of gene expression by RNA-fluorescent in situ hybridisation (FISH) in whole-mount sensory appendages of insects is often impeded by their highly pigmented cuticle. Since most chemical bleaching agents are incompatible with imaging fluorescent-labelled nucleotides, we developed a RNA interference-based method for clearing cuticular pigmentation that allows imaging of fluorescent mRNA in whole-mount appendages of insects. Silencing key genes of the tyrosine-derived pigmentation pathway by injecting dsRNA of laccase2 or tyrosine hydroxylase in two leaf beetles species (Chrysomela populi, Phaedon cochleariae) resulted in clearance of the highly pigmented cuticle and in significant decreased light absorbance. Intact chemosensory appendages (palps, antennae and legs) from RNAi-cleared individuals were used to image expression and spatial distribution of antisense mRNA of two chemosensory genes (gustatory receptor, odorant-binding protein) via RNA FISH and confocal laser scanning microscopy. Imaging of these genes did neither work for RNAi-controls (dsGfp) due to retained pigmentation, nor for FISH-controls using sense mRNA. Furthermore, we show that several chemical bleaching agents are not feasible with FISH, either due to significant degradation of polynucleotides, lack of clearing efficacy or long incubation times. Overall, silencing pigmentation genes is a significant improvement over bleaching agents allowing fluorescence imaging in whole-mount appendages and organs.

molecular biology↗