Biology subjects

Venkatesan, R.

Publications and source records attributed to Venkatesan, R..

17 recordsLinked to original sources

bioRxiv2026

CD14 Blockade Attenuates Arrhythmogenic Cardiomyopathy

Background: Arrhythmogenic cardiomyopathy (ACM) is a genetic and phenotypically heterogeneous myocardial disorder characterized by progressive cardiomyocyte loss, immune cell infiltration, and fibro-fatty replacement of the ventricular myocardium, with an increased risk of sudden cardiac death (SCD), predominantly caused by mutations in cardiac desmosomal genes including PKP2, DSP, and DSG2. We previously described the pivotal role of NF{kappa}B and CCR2+ cardiac macrophage-triggered inflammation in ACM pathogenesis. Methods: WT or Dsg2mut/mut mice were treated with either isotype control or anti-CD14 antibody once a week for the described treatment period (4 or 8 weeks). At the end of the treatment period, disease characteristics were assessed by echocardiography, electrocardiography, histology, immunofluorescence, positron emission tomography (PET) imaging and single-cell transcriptomics. Results: Here, we demonstrate the efficacy of neutralizing CD14 signaling, an important mediator of inflammatory macrophage activation, in attenuating ACM disease in vivo. Additionally, we elucidate shifts in the cellular and transcriptomic landscapes that occur following anti-CD14 antibody treatment in a well-established mouse model of ACM and identify substantial reductions in inflammatory macrophage and pro-fibrotic fibroblast populations. Conclusion: This study provides evidence that blockade of CD14 can attenuate the ACM disease phenotype. It may do so by inhibiting macrophage-based activation and inflammation, while also altering the transcriptional state of other important cell types. Collectively, these findings suggest that CD14 inhibition may be an effective option for ACM, which should be explored in early-phase clinical studies.

immunology↗

bioRxiv2026

Macronutrient balance generates distinct nutritional optima for growth, immune function and stress responses in the specialist herbivore Plutella xylostella

Nutrition plays a fundamental role in insect physiology, yet how variation in dietary macronutrient balance shapes multiple physiological functions remains poorly understood. Using the Geometric Framework for Nutrition, we examined how dietary protein and carbohydrate composition influence growth, immunity and stress physiology in the specialist herbivore Plutella xylostella. Growth depended jointly on protein and carbohydrate availability, whereas immune and oxidative stress traits showed distinct response surfaces across the tested nutrient landscape. Total hemocyte counts and phenoloxidase activity were highest at intermediate protein levels, and survival following Bacillus thuringiensis challenge was likewise associated primarily with protein availability, pointing to a shared nutritional basis for immunity and pathogen resistance. Antioxidant and detoxification enzymes showed trait-specific nutrient responses, indicating that different physiological systems are favored by different macronutrient combinations. No single protein-carbohydrate ratio within the tested landscape simultaneously supported growth, immune performance, and oxidative homeostasis, highlighting trade-offs associated with nutrient allocation across physiological systems. These findings advance understanding of how nutrient-dependent mechanisms coordinate and constrain multiple physiological functions in a specialist herbivore.

ecology↗

bioRxiv2026

Improved crystallization and diffraction quality of Mycobacterium tuberculosis OmamC/Rv1363c upon heat treatment

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, can use host derived lipids as carbon and energy source for survival. Mammalian cell entry (Mce) associated membrane (Mam) proteins are important for the stability of lipid importing Mce complexes. Mtb has five homologs of Mam proteins referred as orphaned Mam (OmamA-E) proteins. A recent study suggested that OmamC (Rv1363c) is essential for the storage and utilization of lipids under starvation in Mtb. To understand the structure and interactions of OmamC, we generated a truncated soluble variant of OmamC (OmamC129-261). Here, we report on the challenges encountered during the crystallization and structure determination of OmamC129-261 and the strategies applied to overcome them. Despite the AlphaFold2 predicted model proving an initial molecular replacement solution, experimental phasing was necessary to determine the structure of OmamC129-261. Heat treatment of protein prior to crystallization setup removed partially unfolded protein present and played a critical role in enhancing the reproducibility and diffraction quality of OmamC129-261 crystals. Although reported earlier, it is not a widely used method. It is worth to try this method, especially, when faced with poor reproducibility and diffraction of crystals.

biochemistry↗

bioRxiv2026

Understanding Conformational Transition of Macrocyclic Peptides through Deep Learning

Molecular conformations play a critical role in determining molecular properties, such as membrane permeability, binding affinity, and ultimately therapeutic efficacy. Experimental and computational approaches can characterize conformations and provide insight into why certain conformations are thermodynamically preferred over others. However, examining conformations alone may not fully explain why subtle differences, such as a single LEU-to-ILE mutation in a bicyclic peptide, can produce markedly distinct conformational ensembles. Analyzing the transition pathways between conformations further reveals the mechanisms that shape these ensembles. Here, we introduce a deep learning model, termed ICoN-v1, trained in molecular dynamics simulation data to learn the underlying physics that governs cyclic peptide conformational dynamics. We examined hexacyclic peptides with Nuclear magnetic resonance (NMR)-determined structures, and MYC-targeting bicyclic peptides, which are stereo-diversified or have a single LEU-to-ILE mutation. By following the minimum-energy pathway in the latent space constructed by ICoN-v1, conformational transition paths, led by various sets of concerted backbone and sidechain torsional rotations moving in sequence between energy minima, are efficiently generated. Notably, smooth transition pathways that are absent from molecular dynamic output can be observed using ICoN-v1. Our results identify various sets of concerted torsional motions that are nonlinearly combined during conformational transitions and reveal the key residues governing each stage of the transition, thereby elucidating how the observed conformations are generated and informing molecular design.

biophysics↗

bioRxiv2025

Insight into the structure and interactions of the M. tuberculosis Mce-associated membrane proteins Mam1A-1D

Tuberculosis (TB) is a major infectious disease caused by Mycobacterium tuberculosis (Mtb), leading to more than a million human deaths every year. Mammalian cell entry complexes (Mce1-4) play an essential role in the survival of Mtb during the latent stage by mediating the import of lipids, including fatty acids and cholesterol, from the host. The proper functioning of Mce-complexes requires additional proteins such as Mce-associated membrane (Mam) proteins and lipid uptake coordinator (LucA), thus making them potential candidates for the development of anti-TB drugs. Four Mam (Mam1A-1D) proteins are coded from the mce1 operon and two from the mce3 (Mam3A-3B) and mce4 (Mam4A-4B) operons. In addition, five orphaned mam (Omam) proteins have been identified, which are not part of the mce operons but are functionally relevant for the Mce complexes. Analysis of the sequences of Mam/Omam proteins suggests that they share many common secondary and tertiary structural elements despite the low sequence identity between them. Here, we have characterized a recombinantly produced Mam1A variant by small-angle X-ray and neutron scattering. The studies indicate that Mam1A is tetrameric in solution with two disulfide bridges necessary for the stability of Mam1A. Similarly, a disulfide bridge has also been identified in Mam1C. Furthermore, through coexpression and copurification, we demonstrate that Mam1A-1D and LucA interact to form stable Mam1ABCD as well as Mam1ABCD-LucA complexes. The results obtained pave the way for further understanding how the Mam1ABCD and Mam1ABCD-LucA complexes are organized and interact with the Mce complexes, leading to their stabilization.

biochemistry↗

bioRxiv2024

Structural enzymological studies of the long chain fatty acyl-CoA synthetase FadD5 from the mce1 operon of Mycobacterium tuberculosis

The cell wall of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, is rich in complex lipids. During intracellular stage, Mtb depends on lipids for its survival. Mammalian cell-entry (Mce) 1 complex encoded by the mce1 operon is a mycolic/fatty acid importer. mce1 operon also encodes a putative fatty acyl-CoA synthetase (FadD5; Rv0166), potentially responsible for the activation of fatty acids imported through the Mce1 complex by conjugating them to Coenzyme A. Here we report that FadD5 is associated to membrane although it can be purified as a soluble dimeric protein. ATP and CoA binding influence FadD5s stability and conformation respectively. Enzymatic studies with fatty acids of varying chain lengths show that FadD5 prefers long chain fatty acids as substrates. X-ray crystallographic studies on FadD5 and its variant reveal that the C-terminal domain ([~]100 residues) is cleaved off during crystallization. Noteworthy, deletion of this domain renders FadD5 completely inactive. SAXS studies, however, confirm the presence of full length FadD5 as a dimer in solution. Further structural analysis and comparisons with homologs provide insights on the possible mode of membrane association and fatty acyl tail binding.

biochemistry↗

bioRxiv2024

Mycolic acid and cholesterol induced transcriptomic adaptations in wild type and Mce complex ATPase subunit deleted strain of M. tuberculosis H37Rv

During infection and latency, Mycobacterium tuberculosis (Mtb) primarily relies on lipids as its main energy source. The Mtb mammalian cell entry (Mce) complexes function as lipid transporters with Mkl as the ATPase subunit for substrate translocation. Cholesterol and mycolic acid are essential to the infectiousness and pathogenicity of Mtb. Here, we have investigated the transcriptomic responses of wild type and{Delta} mkl strains of Mtb to cholesterol and mycolic acid through RNAseq analysis. The number of differentially expressed genes was always higher when grown on cholesterol than on mycolic acid. In most cases,{Delta} mkl showed the opposite gene expression pattern compared to the wild type. Among the four mce operons, significant changes in expression patterns were observed mainly in the genes of mce3 and mce4 operons. The upregulation of mce3 operon and the downregulation of mce4 operon in the presence of mycolic acid and cholesterol is intriguing. The transcriptome profile of genes involved in mycolic acid synthesis did not show significant change to either mycolic acid or cholesterol. However, interestingly, both mycolic acid and cholesterol induce upregulation of methyl citrate cycle and dormancy related genes indicating their significance during Mtb persistence and provides insights on Mtbs adaptive strategies under stress through transcriptional remodelling.

biochemistry↗

bioRxiv2024

Spectral variation and pigmentary basis of ornamental and mimetic wing colour patches of swallowtail butterflies

Colours and colour patterns are extraordinarily diverse traits that are often used as visual signals. To test ecological and evolutionary drivers of these visual signals, a clear understanding of their nature and variation is necessary. Here we characterise variation in wing colouration of Asian mormon swallowtail butterflies (Papilio, subgenus Menelaides). These species exhibit two kinds of colour patches on largely black wings: creamy white/yellow/green patches that are presumably used as sexual ornaments, and pure white patches that are presumably used as mimetic signals. Using reflectance spectrophotometry we quantified spectral properties of black wing background and colour patches between sexes, wing surfaces and mimicry status. We discovered that brightness and saturation of the black background were less variable across sexes, wing surfaces and mimetic/non-mimetic status. However, colour contrast and saturation were higher on dorsal surfaces than on ventral surfaces, and colour contrast between the black background and colour patches was higher in males than in females. Colour patches in non-mimetic butterflies were brighter and more saturated across the whole colour spectrum compared to mimetic butterflies. These patterns of colour variations in relation to their putative functions suggest that: (a) colour patches on dorsal and ventral wing surfaces evolve independently to accommodate differential strengths of natural and sexual selection, (b) sexual ornaments are brighter in non-mimetic males but they also occur in all non-mimetic females, indicating mutual sexual selection on these ornaments, but which is stronger in males, and (c) mimetic male and female butterflies display less sexual contrast in colour patches, indicating relatively similar strength of mimetic selection. Thus, our study characterises colour variation in an extraordinary signal radiation on the wings of swallowtail butterflies, a model clade in ecology, evolution and genetics. Finally, using liquid chromatography-mass spectrometry (LCMS) we identified the pigment papiliochrome-II to be the chemical basis of the presumed sexual ornaments in mormon swallowtails.

evolutionary biology↗

bioRxiv2024

Crystallographic fragment binding studies of the Mycobacterium tuberculosis trifunctional enzyme suggest binding pockets for the tails of the acyl-CoA substrates at its active sites and a potential substrate channeling path between them

The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an 2{beta}2 tetrameric enzyme in which the -chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) active sites, and the {beta}-chain provides the 3-ketoacyl-CoA thiolase (KAT) active site. Linear, medium, and long chain 2E-enoyl-CoA molecules are the preferred substrates of MtTFE. Previous crystallographic binding and modelling studies have identified binding sites for the acyl-CoA substrates at the three active sites as well as the NAD+ binding pocket at the HAD active site. These studies have also identified three additional CoA binding sites on the surface of MtTFE that are different from the active sites. It has been proposed that one of these additional sites could be of functional relevance for substrate channeling (by surface crawling) of reaction intermediates between the three active sites. Here, in a crystallographic fragment binding study with MtTFE crystals 226 fragments were screened, resulting in the structures of 17 MtTFE-fragment complexes. Analysis of the 143 fragment binding events shows that the ECH active site is the binding hotspot for the tested fragments, with 50 binding events. The mode of binding of the fragments bound at the active sites provides additional insight on how the long chain acyl moiety of the substrates can be accommodated at their proposed binding pockets. In addition, the 24 fragment binding events between the active sites identify potential transient binding sites of reaction intermediates relevant for possible channeling of substrates between these active sites. These results provide a basis for further studies to understand the functional relevance of these binding sites and to identify substrates for which channeling is crucial. SynopsisCrystallographic fragment binding studies of the Mycobacterium tuberculosis trifunctional enzyme (MtTFE) have resulted in 143 binding events of 17 fragments out of 226 investigated fragments, suggesting functional sites with respect to substrate binding and substrate channeling.

biochemistry↗

bioRxiv2022

Common and distinct genetic architecture of age at diagnosis of diabetes in South Indian and European populations

South Asians are diagnosed with type 2 diabetes (T2D) more than a decade earlier in life than seen in European populations. We hypothesised that studying the genomics of age of onset in these populations may give insight into earlier age at onset of T2D among individuals of South Asian descent. We conducted a meta-analysis of GWAS of age at diagnosis of T2D in 34,001 individuals from four independent cohorts of European and Asian Indians. We identified two signals near the TCF7L2 and CDKAL1 associated with age at onset of T2D. The strongest genome-wide significant variants at chromosome 10q25.3 in TCF7L2 (lead SNP rs7903146; p = 2.4 x10-12; p-het =0.01; Beta = -0.436; SE = 0.02) and chromosome 6 p22.3 in CDKAL1 (rs9368219; p = 2.29 x10-8; p-het =0.007; Beta = -0.053; SE=0.01) were directionally consistent across ethnic groups and present at similar frequencies, however both loci harboured additional independent signals that were only present in the South Asian cohorts. A genome wide signal was also obtained at chromosome 10q26.12 in WDR11 (rs3011366; p = 2.4 x10-8; p-het =0.25; Beta = 1.44; SE=0.25) specifically in the South Asian Indian cohorts. Our study estimated 17% of heritability (h2) for age onset of T2D among South Indians; higher than the 5% heritability we observed in Europeans suggesting different genetic architectures between these populations. We further estimated the Asian Indian genome-wide polygenic risk score for T2D risk and identified that the variance explained by the Indian specific polygenic risk score (PRS) for age at onset of T2D is substantially higher (2%) in an independent cohort of Asian Indians compared to that seen in White Europeans (<0.1%). This reveals that although variants do exist that are shared between the two population there are also genetic disparities of age onset of T2D between the ethnicities. Author SummaryRecent large multi-ancestry genome-wide meta-analyses have identified over 277 genetic loci associated with type 2 diabetes (T2D). Most association studies for T2D have focused on populations of European ancestry, and the specific genetic architecture of T2D in the South Asian population has not been extensively investigated. Increasing evidence indicates that the prevalence of T2D is higher in South Asians with a strikingly earlier age at diagnosis when compared to Europeans. Genome-wide association studies (GWAS) on age at age at diagnosis of T2D are limited and can help elucidate underlying mechanisms. We conducted the largest meta-analysis to date of genome-wide association studies of age at diagnosis as a surrogate for age of onset of T2D in South Indians and Europeans. Our trans-ancestry meta-analysis identified genetic loci near TCF7L2 and CDKAL1 with substantial ethnic heterogeneity in both allele frequencies and effect sizes in early diagnosis with T2D. Two novel variants near TCF7L2 (rs570193324) and CDKAL1 (rs143316471) were associated with age of diagnosis of T2D only in South Indians and were present at much lower frequency in the European populations. Heritability estimates for age of onset were much stronger in Asian Indians compared to Europeans and a polygenic risk score was constructed using a South Indians, which explained about 2% trait variance compared to European ancestry (<0.1%). Our novel findings provide a better understanding of ethnic differences in the age at onset of T2D and indicate the potential importance of ethnic differences in the genetic architecture underpinning T2D.

genetics↗

bioRxiv2022

iPheGWAS : an intelligent computational framework to integrate and visualise genome-phenome wide association studies

Estimating the genetic correlations by LDSC is computationally demanding and visualising multiple GWAS results along with their genetic relationships is restricted. This study developed iPheGWAS, a novel approach which applied hierarchical clustering to GWAS summary statistics to (i) calculate their genetic relatedness, and (ii) enable three-dimensional visualisation of multiple ordered GWAS plots. Simulation and real-world data analysis demonstrated that when investigating genetic relationships among multiple phenotypes, iPheGWAS can deliver comparable results with LDSC but with 8 times faster computational speed. It can also provide novel findings in studying genetically-correlated comorbidities, such as mental illness and rheumatoid arthritis.

bioinformatics↗

bioRxiv2021

Disulfide-rich, cyclic peptides from Clitoria ternatea protect against β-amyloid toxicity and oxidative stress in transgenic Caenorhabditis elegans

Neurotoxic aggregation of {beta}-amyloid (A{beta}) peptide is a hallmark of Alzheimers disease and increased reactive oxygen species (ROS) is known to be associated with this. Here, we report neuroprotective effects of disulfide-rich, circular peptides from Clitoria ternatea on A{beta}-induced toxicity in transgenic Caenorhabditis elegans. We show that cyclotide-rich fractions from different plant tissues delay A{beta}-induced paralysis in transgenic CL4176 strain expressing human muscle-specific A{beta}1-42 gene. It also improved A{beta}-induced defects in chemotaxis in CL2355 expressing A{beta}1-42 in neuronal cells. ROS assay suggests that this is likely mediated by inhibition of A{beta} oligomerization. Further, A{beta} deposits were reduced in the strain, CL2006 treated with the fractions. Computational docking and molecular dynamics (MD) simulation support the findings since cyclotides bind effectively and stably to different forms of A{beta} structures via hydrogen bonding and hydrophobic interactions. MD simulation further shows that cyclotides destabilize toxic amyloid assemblies. The study shows that cyclotides from C. ternatea could be a source of novel pharmacophore scaffold against neurodegenerative diseases.

plant biology↗

bioRxiv2020

Structural insights on the substrate-binding proteins of the Mycobacterium tuberculosis mammalian-cell-entry (Mce) 1 and 4 complexes

Tuberculosis (Tb), caused by Mycobacterium tuberculosis (Mtb), is responsible for more than a million deaths annually. In the latent phase of infection, Mtb uses lipids as the source of carbon and energy for its survival. The lipid molecules are transported across the cell wall via multiple transport systems. One such set of widely present and less-studied transporters is the Mammalian-cell-entry (Mce) complexes. Here, we report the properties of the substrate-binding proteins (SBPs; MceA-F) of the Mce1 and Mce4 complexes from Mtb which are responsible for the import of mycolic acid/fatty acids, and cholesterol respectively. MceA-F are composed of four domains namely, transmembrane, MCE, helical and tail domains. Our studies show that MceA-F are predominantly monomeric when purified individually and do not form homohexamers unlike the reported homologs (MlaD, PqiB and LetB) from other prokaryotes. The crystal structure of MCE domain of Mtb Mce4A (MtMce4A39-140) determined at 2.9 [A] shows the formation of an unexpected domain-swapped dimer in the crystals. Further, the purification and small-angle X-ray scattering (SAXS) analysis on MtMce1A, MtMce4A and their domains suggest that the helical domain requires hydrophobic interactions with the detergent molecules for its stability. Combining all the experimental data, we propose a heterohexameric arrangement of MtMceA-F SBPs, where the soluble MCE domain of the SBPs would remain in the periplasm with the helical domain extending to the lipid layer forming a hollow channel for the transport of lipids across the membranes. The tail domain would reach the cell surface assisting in lipid recognition and binding.

biochemistry↗

bioRxiv2020

Circulating adiponectin mediates the association between omentin gene polymorphism and cardiometabolic health in Asian Indians

BackgroundPlasma omentin levels have been shown to be associated with circulating adiponectin concentrations and cardiometabolic disease-related outcomes. However, the findings have been inconsistent due to high level of confounding. In this study, we aim to examine the association of omentin gene polymorphism with plasma adiponectin levels and cardiometabolic health status using a genetic approach, which is less prone to confounding, and investigate whether these associations are modified by lifestyle factors such as diet and physical activity. MethodsThe study included 945 normal glucose tolerant and 941 unrelated individuals with type 2 diabetes randomly selected from the Chennai Urban Rural Epidemiology Study (CURES), in southern India. Study participants were further classified into cardiometabolically healthy and unhealthy, where cardiometabolically healthy were those without hypertension, diabetes, and dyslipidemia. Fasting serum adiponectin levels were measured by radioimmunoassay. The A326T (rs2274907) single nucleotide polymorphism (SNP) in the exon 4 of the omentin gene was screened by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing. ResultsThe A allele of the omentin SNP was significantly associated with lower adiponectin concentrations after adjusting for age, sex, body mass index (BMI), waist circumference (WC) and cardiometabolic health status (p=1.90 x 10-47). There was also a significant association between circulating adiponectin concentrations and cardiometabolic health status after adjusting for age, sex, BMI, WC and Omentin SNP (p=7.47x10-10). However, after adjusting for age, sex, BMI, WC and adiponectin levels, the association of A allele with cardiometabolic health status disappeared (p=0.79) suggesting that adiponectin serves as a mediator of the association between omentin SNP and cardiometabolic health status. There were no significant interactions between the SNP and dietary factors on adiponectin levels and cardiometabolic health status (p>0.25, for all comparisons). ConclusionsOur findings show that adiponectin might function as a mechanistic link between omentin SNP and increased risk of cardiometabolic diseases independent of common and central obesity in this Asian Indian population. Further studies are required to confirm the molecular mechanisms involved in this triangular relationship between omentin gene, adiponectin and cardiometabolic diseases.

genetics↗

bioRxiv2020

Performance of Bracon brevicornis (Wesmael) on two Spodoptera species and application as potential biocontrol agent against fall armyworm

Successful pest management using parasitoids requires careful evaluation of host-parasitoid interactions. Here, we report the performance of larval ecto-parasitoid wasp, Bracon brevicornis (Wesmael) on important agricultural pests, Spodoptera litura (Fabricius) and S. frugiperda (J.E. Smith). Biology of B. brevicornis was studied on different host instars under laboratory and cage setup. In no-choice assay, the parasitoid development was highest on fifth instar S. litura larvae as the wasp laid ∼253 eggs with 62% hatching, 76% pupae formation and 78% adult emergence. Similarly, these parameters were highest on fifth instar S. frugiperda larvae (293 eggs, 57% hatching, 80% pupae formation, 70% adult emergence). In two-choice assay, B. brevicornis preferred fourth or fifth over third instar larvae of both hosts. Successful parasitism depends on host paralysis and suppression of host immunity. B. brevicornis interaction downregulated cellular immunity of both hosts as shown by reduced hemocyte viability and spreading. The percent parasitism rate of B. brevicornis was unaltered in the presence of host plant, Zea mays in cage study. 76 and 84% parasitism was observed on fifth instar larvae of S. litura and S. frugiperda, respectively. We evaluated the performance of B. brevicornis as a biocontrol agent on S. frugiperda in maize field. Our results show 54% average reduction in infestation after release of B. brevicornis. Taken together, we report the performance of B. brevicornis on important insect pests for the first time in laboratory and field conditions. Our findings indicate that B. brevicornis is a promising candidate for integrated pest management.Key messagesWe have evaluated the instar preference and performance of B. brevicornis as a potential biocontrol agent for two serious pests, Spodoptera litura and S. frugiperda.Fifth instar larva was most suitable for B. brevicornis development irrespective of the host species. B. brevicornis attack induced permanent paralysis and down-regulated cellular immunity of both hosts.Our field experiment confirmed B. brevicornis as a promising parasitoid for controlling S. frugiperda, a highly invasive pest of growing concern.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗

bioRxiv2019

Phenotypic diversity of Methylobacterium associated with rice landraces in Northeast India

The ecology and distribution of many bacteria is strongly associated with specific eukaryotic hosts. However, the impact of such host association on bacterial ecology and evolution is not well understood. Bacteria from the genus Methylobacterium consume plant-derived methanol, and are some of the most abundant and widespread plant-associated bacteria. In addition, many of these species impact plant fitness. To determine the ecology and distribution of Methylobacterium in nature, we sampled bacteria from 36 distinct rice landraces, traditionally grown in geographically isolated locations in North-East (NE) India. These landraces have been selected for diverse phenotypic traits by local communities, and we expected that the divergent selection on hosts may have also generated divergence in associated Methylobacterium strains. We determined the ability of 91 distinct rice-associated Methylobacterium isolates to use a panel of carbon sources, finding substantial variability in carbon use profiles. Consistent with our expectation, across spatial scales this phenotypic variation was largely explained by host landrace identity rather than geographical factors or bacterial taxonomy. However, variation in carbon utilisation was not correlated with sugar exudates on leaf surfaces, suggesting that bacterial carbon use profiles do not directly determine bacterial colonization across landraces. Finally, experiments showed that at least some rice landraces gain an early growth advantage from their specific phyllosphere-colonizing Methylobacterium strains. Together, our results suggest that landrace-specific host-microbial relationships may contribute to spatial structure in rice-associated Methylobacterium in a natural ecosystem. In turn, association with specific bacteria may provide new ways to preserve and understand diversity in one of the most important food crops of the world.

ecology↗

bioRxiv2017

FEMALE CHEMICAL WARFARE DRIVES FITNESS EFFECTS OF GROUP SEX RATIO

In animals, skewed sex ratios can affect individual fitness either via sexual interactions (e.g. intersexual conflict or intrasexual mate competition) or non-sexual interactions (e.g. sex-specific resource competition). Because most analyses of sex ratio focus on sexual interactions, the relative importance of these mechanisms remains unclear. We addressed this problem using the flour beetle Tribolium castaneum, where male-biased sex ratios increase female fitness relative to unbiased or female-biased groups. Although flour beetles show both sexual and non-sexual (resource) competition, we found that sexual interactions did not explain female fitness. Instead, female fecundity was dramatically reduced even after a brief exposure to flour conditioned by other females. Earlier studies suggested that quinones (secreted toxins) might mediate density-dependent population growth in flour beetles. We identified ethyl- and methyl-benzoquinone (EBQ and MBQ) as the primary components of adult stink glands that regulate female fecundity. In female-biased groups (i.e. at high female density), females upregulated quinones and suppressed each others reproduction. In male-biased groups, low female density lead to low quinone levels, allowing higher fecundity. Thus, quinones serve both as indicators and mediators of female competition, resulting in the observed fitness decline in female-biased groups. Our results underscore the importance of non-sexual interference competition that may often underlie the fitness consequences of skewed sex ratios.

evolutionary biology↗