Biology subjects

Halitschke, R.

Publications and source records attributed to Halitschke, R..

10 recordsLinked to original sources

bioRxiv2025

Metabolic plasticity supports a flexible nutritional symbiosis in Cardiocondyla ants

Nutritional symbioses have repeatedly evolved in insects, yet how hosts regulate these partnerships to balance benefits across development and environments remains unclear. Ants provide an exceptional system to address this question, as several lineages maintain ancient symbionts that can be naturally lost without harming the host. Using Cardiocondyla obscurior, which carries and occasionally loses the vertically transmitted symbiont Cand. Westeberhardia cardiocondylae, we reveal the regulatory dynamics and function of this labile association. Symbionts provide shikimate-derived nutrients that enhance colony resilience under protein limitation, while hosts actively regulate symbiont abundance during protein scarcity and cuticle formation to optimise resource allocation. In the symbionts absence, ants compensate by upregulating genes enabling tyrosine acquisition from external sources. This metabolic flexibility allows colonies to exploit symbiont-derived and environmental nutrients, sustaining both growth and survival across nutritional contexts. Our findings reveal dynamic host regulation as a mechanism sustaining the persistence and adaptability of ancient symbioses.

ecology↗

bioRxiv2025

Offspring chemical control of adult reproductive transitions in a social insect

Parental care enhances offspring survival and growth but often entails a trade-off in which caregivers temporarily suppress their own reproduction to invest in existing young. In vertebrates, these parental reproductive cycles are controlled by offspring-derived cues that reduce or suppress parental fertility. While many insects display obligate parental care, the role of offspring cues in regulating adult reproduction remains unresolved outside advanced eusocial taxa, where reproductive cycles have largely been lost. Here, we investigate reproductive cycles in the clonal raider ant Ooceraea biroi, in which totipotent females alternate between caring for larvae and laying eggs. Using custom behavioral assays, we show that larvae inhibit adult reproduction without physical contact, implicating volatile cues. Chemical analyses identified a previously undescribed larva-specific compound, methyl 3-ethyl-2-hydroxy-4-methylpentanoate (MEHMP), which is absent from other developmental stages and ant species. Exposure to synthetic MEHMP recapitulated the inhibitory effect of larval volatiles, confirming its role as a pheromone that suppresses adult egg laying. To our knowledge, this is the first brood pheromone described in ants. By providing a direct chemical link between offspring presence and parental reproductive suppression, our findings underscore the central role of offspring signals in mediating parental reproductive investment across animals that care for their young. Significance StatementParental care enhances offspring survival but induces profound physiological changes in caregivers. A common feature across animals is that adults temporarily suppress their own reproduction while caring for the young. The offspring cues enforcing these cycles remain poorly understood, especially in insects. Using the clonal raider ant Ooceraea biroi, in which all females alternate between reproduction and brood care, we identify a larval pheromone that suppresses adult egg laying. This pheromone is a previously undescribed volatile chemical compound, and exposure to its synthetic version mimics the full biological effect of larvae volatiles. By providing a direct link between offspring presence and adult reproductive suppression, our work highlights how offspring can chemically control the reproduction of their caregivers.

animal behavior and cognition↗

bioRxiv2024

Immunity and bacterial recruitment in plant leaves are parallel processes whose link shapes sensitivity to temperature stress

Rising global temperatures necessitate developing resilient crops with better adaptability to changing climates. Under elevated temperatures, plant immunity is downregulated, increasing risk of foliar pathogen attack. Manipulating plant defense hormones is one way to mitigate this detrimental effect. However, it is unclear how plant immunity interacts with plant microbiome assembly and how temperature will thus affect overall plant health and stability. In this study, we compared two Arabidopsis thaliana genotypes that feature divergent strategies for recruitment of commensal bacteria from natural soil. NG2, an A. thaliana ecotype we collected from Jena, Germany, was grown in its native soil and compared to CLLF, a genotype that recruits higher bacterial loads and higher bacterial diversity but without any dysbiotic phenotype. CLLF hyperaccumulates salicylic acid (SA) and jasmonates, has constitutively upregulated innate defenses, and shows increased resistance to necrotrophic fungal and hemi-biotrophic bacterial pathogens, indicating that pathogen immunity and non-pathogen recruitment function in parallel. Some of its leaf bacteria can utlize SA as a carbon source, suggesting that immunity and recruitment may even be linked by chemical hormones. CLLF exhibits high tolerance to heat stress in comparison to the NG2, with SA-associated defense processes remaining active under heat. Synthetic community (SynCom) experiments revealed that when the taxonomic diversity of bacteria available to CLLF is artificially reduced, resilience to heat stress is compromised, leading to dysbiosis. However, this dysbiosis does not occur in CLLF with a full SynCom or in the NG2 with any SynCom. These findings suggest that the downregulation of defenses in response to heat may contribute to the avoidance of dysbiosis caused by certain leaf bacteria, while full bacteriome taxonomic diversity can help maintain balance.

microbiology↗

bioRxiv2024

Three cytochrome P450 from Nicotiana attenuata play key roles in triterpene biosynthesis

Pentacyclic triterpenoids, recognized for their natural bioactivity, display complex spatiotemporal accumulation patterns within the ecological model plant, Nicotiana attenuata. Despite their ecological significance, the underlying biosynthetic enzymes and functional attributes of triterpenoid synthesis in N. attenuata remain unexplored. Three multifunctional cytochrome P450 monooxygenases (NaCYP716A419, NaCYP716C87, NaCYP716E107) from N. attenuata were shown to oxidize the pentacyclic triterpene skeleton as evidenced by heterologous expression in Nicotiana benthamiana. NaCYP716A419 catalyzed a consecutive three-step oxidation reaction at the C28 position of {beta}-amyrin/lupeol/lupanediol, yielding the corresponding alcohol, aldehyde, and carboxylic acid. NaCYP716C87 hydroxylated the C2 position of {beta}-amyrin/lupeol/lupanediol/erythrodiol/oleanolic acid/betulinic acid, while NaCYP716E107 hydroxylated the C6{beta} position of {beta}-amyrin/oleanolic acid. Three CYP716 enzymes are highly expressed in flowers and respond to induction by ABA, MeJA, SA, GA3, and abiotic stress treatments. Using VIGS technology, we revealed that silencing of NaCYP716A419 affects the growth and reproduction of N. attenuata, suggesting the ecological significance of these specialized metabolite biosynthetic steps. One-sentence summaryThree CYP716 enzymes diversify N. attenuatas triterpenoid sector with potential roles in growth and development.

plant biology↗

bioRxiv2023

Association of leaf spectral variation with functional genetic variants

The application of in-field and aerial spectroscopy to assess functional and phylogenetic variation in plants has led to novel ecological insights and supports global assessments of plant biodiversity. Understanding how plant genetic variation influences reflectance spectra will help harness this potential for biodiversity monitoring and improve understanding of why plants differ in functional responses to environmental change. Here, we use a well-resolved genetic mapping population derived from Multi-parent Advanced Generation Inter-cross (MAGIC) lines of Nicotiana attenuata to associate genetic differences with differences in leaf spectra between plants in a field experiment in their natural environment. We analyzed the leaf reflectance spectra using a hand-held spectroradiometer (350-2500 nm) on 616 fully genotyped plants of N. attenuata grown in a randomized block design. We tested three approaches to conducting Genome-Wide Association Studies on spectral variants. We introduce a new Hierarchical Spectral Clustering with Parallel Analysis (HSC-PA) method. This method efficiently captured the variation in our high-dimensional dataset and allowed us to discover a novel association, between a locus on chromosome 1 and the 734-1143 nm spectral range, spanning the red-edge and near-infrared regions that are sensitive to leaf structure and photosynthetic activity. This locus contains a candidate gene annotated as carbonic anhydrase, an enzyme involved in CO2 hydration and regulation of photosynthetic efficiency, suggesting a physiological link between variation in leaf optical properties and carbon assimilation. In contrast, an approach treating single wavelengths as phenotypes identified the same associations as HSC-PA, but without the statistical power to pinpoint significant associations. An index-based approach, which reduces complex spectra to a few dimensionless variables, detected two significant associations for ARDSI_Cw (a water-content-related index) with loci on chromosome 1 near genes annotated as a Zeta toxin domain-containing protein, and an Exocyst subunit Exo70 family protein. While these findings are biologically plausible, they represent a very narrow subset of the spectral variation captured by HSC-PA. The HSC-PA approach supports a comprehensive understanding of the genetic determinants of leaf spectral variation which is data-driven but human-interpretable, and lays a robust foundation for future research in linking plant genetics with biodiversity monitoring, large-scale ecological assessment and remote-sensing applications.

ecology↗

bioRxiv2022

Heterologous expression of PtAAS1 reveals the metabolic potential of the common plant metabolite phenylacetaldehyde for auxin synthesis in planta

Aromatic aldehydes and amines are common plant metabolites involved in several specialized metabolite biosynthesis pathways. Recently, we showed that the aromatic aldehyde synthase PtAAS1 and the aromatic amino acid decarboxylase PtAADC1 contribute to the herbivory-induced formation of volatile 2-phenylethanol and its glucoside 2-phenylethyl-{beta}-D-glucopyranoside in Populus trichocarpa. To gain insights into alternative metabolic fates of phenylacetaldehyde and 2-phenylethylamine beyond alcohol and alcohol glucoside formation, we expressed PtAAS1 and PtAADC1 heterologously in Nicotiana benthamiana and analyzed plant extracts using untargeted LC-qTOF-MS analysis. While the metabolomes of PtAADC1-expressing plants did not significantly differ from those of control plants, expression of PtAAS1 resulted in the accumulation of phenylacetic acid (PAA) and PAA-amino acid conjugates, identified as PAA-aspartate and PAA-glutamate. Moreover, targeted LC-MS/MS analysis showed that PtAAS1-expressing plants accumulated significant amounts of free PAA. The measurement of PAA and PAA-Asp in undamaged and herbivory-damaged poplar leaves revealed significantly induced accumulation of PAA-Asp while levels of free PAA remained unaltered by herbivore treatment. Sequence comparisons and transcriptome analysis showed that members of a small gene family comprising five putative auxin-amido synthetase GH3 genes potentially involved in the conjugation of auxins like PAA with amino acids were significantly upregulated upon herbivory in P. trichocarpa leaves. Overall, our data indicates that phenylacetaldehyde generated by poplar PtAAS1 serves as a hub metabolite linking the biosynthesis of volatile, non-volatile herbivory-induced specialized metabolites, and phytohormones, suggesting that growth and defense are balanced on a metabolic level.

plant biology↗

bioRxiv2020

Specific decorations of 17-hydroxygeranyllinalool diterpene glycosides solve the autotoxicity problem of chemical defense in Nicotiana attenuata

17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) are abundant and potent anti-herbivore defense metabolites in Nicotiana attenuata whose glycosylation and malonylation biosynthetic steps are regulated by jasmonate signaling. To characterize the biosynthetic pathway of HGL-DTGs, we conducted a genome-wide analysis of uridine diphosphate glycosyltransferases (UGTs) and identified 107 members of family-1 UGTs. Tissue-specific time-course transcriptional profiling revealed that the transcripts of three UGTs were highly correlated with two HGL-DTG key biosynthetic genes: geranylgeranyl diphosphate synthase (NaGGPPS) and geranyllinalool synthase (NaGLS). NaGLSs role in HGL-DTG biosynthesis was confirmed by virus-induced gene-silencing. Silencing the UDP-rhamnosyltransferase, UGT91T1, indicated its role in the rhamnosylation of HGL-DTGs. In vitro enzyme assays revealed that UGT74P3 and UGT74P4 use UDP-glucose for the glucosylation of 17-hydroxygeranyllinalool (17-HGL) to lyciumoside I. UGT74P3 and UGT74P5 stably silenced plants were severely developmentally deformed, suggesting a phytotoxic effect of 17-HGL. Applications of synthetic 17-HGL and silencing of these UGTs in HGL-DTG-free plants confirmed the phytotoxic effect of 17-HGL. Feeding assays with Manduca sexta larvae revealed the defensive functions of the glucosylation and rhamnosylation steps in HGL-DTG biosynthesis. Glucosylation is a critical step that contributes to the metabolites defensive function and solves the autotoxicity problem of this potent chemical defense.

plant biology↗

bioRxiv2020

Predation drives specialized host plant associations in preadapted milkweed bugs (Heteroptera: Lygaeinae)

Host plant specialization across herbivorous insects varies dramatically, but the underlying evolutionary mechanisms are little-known. The milkweed bugs (Heteroptera: Lygaeinae) are ancestrally associated with plants of the Apocynaceae from which they commonly sequester cardiac glycosides for defense, facilitated by resistant Na+/K+-ATPases and adaptations for transport, storage and discharge of toxins. Here, we show that three Lygaeinae species independently colonized four novel non-apocynaceous hosts, convergently producing cardiac glycosides. A fourth species shifted to a new source of toxins by tolerating and sequestering alkaloids from meadow saffron (Colchicum autumnale, Colchicaceae). Across three species tested, feeding on seeds containing toxins did not improve growth, but sequestration mediated protection against predatory lacewing larvae and birds. We conclude that physiological preadaptations and convergent phytochemistry facilitated novel specialized host associations. Therefore, selection by predators on sequestration of defenses, rather than the exploitation of novel dietary resources, can lead to obligatory specialized host associations in generalist insects.

evolutionary biology↗

bioRxiv2020

Information theory tests critical predictions of plant defense theory for specialized metabolism

Different plant defense theories have provided important theoretical guidance in explaining patterns in plant specialized metabolism, but their critical predictions remain to be tested. Here, we systematically explored the metabolomes of Nicotiana attenuata, from single plants to populations, as well as of closely-related species, using unbiased MS/MS analyses and processed the abundances of compound-spectrum-based MS features within an information theory framework to test critical predictions of Optimal Defense (OD) and Moving Target (MT) theories. Information components of herbivory-elicited plant metabolomes were fully consistent with the OD theory predictions and contradicted the main prediction of the MT theory. From micro- to macro-evolutionary scales, jasmonate signaling was identified as the master determinant of OD while ethylene signaling provided fine-tuning for herbivore-specific responses annotated via MS/MS molecular networks. One-sentence summaryInformation theory tests defense theory predictions by providing a common currency for comparison of specialized metabolomes

plant biology↗

bioRxiv2019

Determining the scale at which variation in WUE traits changes population yields

Functional variation is known to influence population yield, but the scale at which this happens is still unknown. Relevant signals might only reach immediate neighbors of a phenotypically diverse plant (neighbor-scale) or conversely may distribute across the population (population-scale). We use Nicotiana attenuata silenced in mitogen-activated protein kinase 4 (irMPK4), plants with low water-use efficiency (WUE), to study the scale at which water-use traits alter intraspecific population yields. In the field and glasshouse, populations with low percentages of irMPK4 plants planted among isogenic control plants produced maximum overall growth and yield. Through paired-plant and local-plant-configuration analyses, we determined that this occurred at the population scale. However, we find that this effect was not due to irMPK4s WUE phenotype. With micro-grafting, we additionally show that MPK4-deficiency may mediate the response at the population-scale: shoot-expressed MPK4 is required for N. attenuata to change yield in response to a neighbor.

ecology↗