Biology subjects

Ahmed, M. A.

Publications and source records attributed to Ahmed, M. A..

8 recordsLinked to original sources

bioRxiv2026

Beyond air-seeding: Dynamic, multiphase interactionsreveal a two-step mechanism of embolism propagation inangiosperm xylem

BackgroundThe mechanism underlying drought-induced embolism in angiosperm xylem has been attributed to air-seeding. This concept describes the bulk flow of gas from embolised to neighbouring conduits through the penetration of gas-liquid menisci across pores in interconduit pit membranes. While there is compelling evidence for the spatial propagation of embolism, air-seeding rests on various simplifying assumptions. Among others, air-seeding presumes that xylem sap has physical properties comparable to pure water, that pit membranes can be approximated as structures with simple pores, and that embolism occurs whenever a gas-liquid interface crosses a pit membrane. ScopeRecent experimental and theoretical work demonstrates that the biophysical conditions and processes governing gas-liquid interactions at interconduit pit membranes are fundamentally more dynamic and complex than assumed by air-seeding. These phenomena include: (1) gas movement through constriction pore networks, (2) insoluble, polar lipids at conduit surfaces and interfaces, (3) dynamic surface tension of xylem sap that depends on the local packing density of interfacial lipids, (4) bubble snap-off dynamics within pit membranes, (5) surfactant-stabilized nanobubbles in sap that is oversaturated with dissolved gas, and (6) electrostatic interactions between charged interfaces. Importantly, embolism propagation involves bubble generation and embolism formation as distinct, temporarily and spatially separated processes. Embolism formation occurs when nanobubbles become unstable, whereas nanobubbles below critical stability thresholds can remain stable in sap-filled conduits. ConclusionsTogether, these findings reconfirm that pit membranes function as safety valves enabling water transport according to the cohesion-tension theory, and provide mechanistic insights into embolism propagation. They address the question why plants do not suffer constant embolism formation despite negative xylem pressures. We conclude that a revised framework explicitly accounting for the 3D structure of pit membranes, and multiphase, dynamic processes operating within them are required to explain the biophysics underlying water transport and embolism resistance in angiosperm xylem.

plant biology↗

bioRxiv2025

Ecological distribution, environmental roles and drivers of Actinobacteriota in two Mid-Atlantic estuaries

Actinobacteriota, a bacterial phylum renowned for members that produce bioactive compounds (e.g., antibiotics), has key roles in terrestrial and aquatic ecosystems. Although soil and marine/freshwater Actinobacteriota are well studied, functions and activities of their estuarine counterparts are poorly understood. We characterized 67 metagenome-assembled genomes (MAGs) belonging to 12 Actinobacteriota families from Chesapeake and Delaware Bay water samples across different seasons, salinities, and size fractions. MAGs from four dominant families, Ilumatobacteraceae, Nanopelagicaceae, Microbacteriaceae, and S36-B12, were examined in depth for their abundance, functional potential, estimated growth rates, and gene expression among samples. Actinobacteriota were most abundant in low- to medium-salinity samples during spring and summer. Their abundance patterns were strongly influenced by combinations of salinity, temperature, and phosphate, nitrate and silicate concentrations. Notably, many exhibited high estimated growth rates under low and medium salinities in summer. Members of the four major families showed a range of metabolic capacities from generalist to specialist, and all encoded biosynthetic gene clusters (BGCs) for secondary metabolites, particularly terpenes and betalactones, that were differentially expressed across conditions. Bay, salinity and size fraction were the primary drivers of gene expression differences. Distinct secondary metabolite genes were expressed between bays, with higher expression generally observed in medium compared to low salinities. These findings underscore the metabolic versatility and environmental responsiveness of Actinobacteriota, highlighting their active role in estuarine microbial communities and their contributions to biogeochemical cycling in dynamic coastal ecosystems. ImportanceEstuaries are dynamic transition zones where microbial communities play key roles in nutrient cycling and ecosystem functioning. This study provides new insights into the distribution of Actinobacteriota families and their responses to salinity and nutrient gradients in two major U.S. estuaries, the Chesapeake and Delaware Bays. We characterized the potential roles of Actinobacteriota in biogeochemical processes and secondary metabolite production, which may influence broad microbial interactions. These bacteria may also serve as a source of novel bioactive compounds, including antibiotics. By integrating omic and environmental data, this work advances our understanding of Actinobacteriota adaptations and their ecology in estuarine environments.

microbiology↗

bioRxiv2024

Nano-org, a functional resource for single-molecule localisation microscopy data

We present a publicly accessible, curated, and functional resource, termed "nano-org", containing single-molecule localisation microscopy (SMLM) data representing the nanoscale distributions of proteins in cells. Nano-org is searchable by comparing the statistical similarity of the datasets it contains. This unique functionality allows the resource to be used to understand the relationships of nanoscale architectures between proteins, cell types or conditions, enabling a new field of spatial nano-omics.

biophysics↗

bioRxiv2022

Epitopes- Based Vaccine Design Against Foot and Mouth Disease SAT2 Serotype from Sudanese Isolate by Using Immunoinformatic Approaches

Foot and mouth disease (FMD) has been endemic in Sudan for decades and causes continuous outbreaks that have a direct negative impact on the animal population and prevent the exportation of animals from the country. The high diversity of FMD serotypes, especially SAT2 and A serotypes, hinders the development of effective vaccines since the most important component of vaccination is the degree of cross-protection provided by the vaccine against currently circulating field viruses. An immunoinformatic approach was utilized to predict a multi-epitope peptide vaccine design against the SAT2 serotype from a Sudanese isolate targeting virus capsid region P1. The virus capsid region P1 comprises the major immunogenic epitopes that confer protection against the FMD virus. Two predicted T-cell epitopes were identified that showed high binding affinity with MHC1 alleles (VQRSRQSTL and YHAEWDTGL) and high conservation with SAT2 African serotypes and were located within the VP1 and VP3 proteins, respectively. Only one epitope was predicted for B cells (LPATPEDAAH), which scored above the threshold in Bepipred linear epitope, Emini surface accessibility, and Kolaskar and Tongaonkar antigenicity and is located in VP3 protein. Molecular docking of the peptides (VQRSRQSTL and YHAEWDTGL) with the MHC1 allele showed satisfactory interaction with the binding sites of BoLA-HD6 using UCSF chimera 1.13.1 software. The peptide VQRSRQSTL showed remarkable hydrophobic interaction with the BoLA-HD6 allele, which was superior to the other peptides. This study is the first to propose a peptide vaccine against FMD SAT2 serotypes from a Sudanese isolate.

bioinformatics↗

bioRxiv2022

Influence of amino acids and glucosinolates in three Brassicaceae vegetable plants on preference and performance of the green peach aphid: Myzus persicae

The green peach aphid, Myzus persicae (Sulzer) is a generalist pest of various host plants, whose feeding preference and growth performance mainly depends on the quantity and quality of nutrients and defensive metabolites in host plants. Here, we studied the preference and performance of M. persicae on three major Brassicaceae vegetables in China and measured nutrient (amino acids) and defensive (glucosinolates) metabolites in these plants. We found that M. persicae preferred and performed better on Chinese cabbage than cabbage and radish, which may be due to the relatively higher concentration of amino acids and lower levels of glucosinolates in their leaves. The glucosinolates level in cabbage leaves was ten times higher than the other two plants, while the amino acid concentration in radish was only half of the cabbage or Chinese cabbage. The higher concentration of glucosinolates in cabbage and lower levels of amino acids in radish may account for the poorer preference and growth of M. persicae on these two plants. These results suggest that both amino acids and glucosinolates in plants are important determinants of the preference and performance of M. persicae, which provide new knowledge for the cultivation and breeding of Brassicaceae vegetables.

ecology↗

bioRxiv2021

Engaging Biological Oscillators through Second Messenger Pathways Permits Emergence of a Robust Gastric Slow-Wave during Peristalsis

Peristalsis, the coordinated contraction - relaxation of the muscles of the stomach is important for normal gastric motility and is impaired in motility disorders. Coordinated electrical depolarizations that originate and propagate within a network of interconnected layers of interstitial cells of Cajal (ICC) and smooth muscle (SM) cells of the stomach wall as a slow-wave, underly peristalsis. Normally, the gastric slow-wave oscillates with a single period and uniform rostrocaudal lag, exhibiting network entrainment. Understanding of the integrative role of neurotransmission and intercellular coupling in the propagation of an entrained gastric slow-wave, important for understanding motility disorders, however, remains incomplete. Using a computational framework constituted of a novel gastric motility network (GMN) model we address the hypothesis that engaging biological oscillators (i.e., ICCs) by constitutive gap junction coupling mechanisms and enteric neural stimulus activated signals can confer a robust entrained gastric slow-wave. We demonstrate that while a decreasing enteric neural stimulus gradient that modulates the intracellular IP3 concentration in the ICCs can guide the aboral slow-wave propagation essential for peristalsis, engaging ICCs by recruiting the exchange of second messengers (inositol trisphosphate (IP3) and Ca2+) ensures a robust entrained longitudinal slow-wave, even in the presence of biological variability in coupling strengths. Our GMN with the distinct intercellular coupling in conjunction with the intracellular feedback pathways and a rostrocaudal enteric neural stimulus gradient allows gastric slow waves to oscillate with a moderate range of frequencies and to propagate with a broad range of velocities, thus preventing decoupling observed in motility disorders. Overall, the findings provide a mechanistic explanation for the emergence of decoupled slow waves associated with motility impairments of the stomach, offer directions for future experiments and theoretical work, and can potentially aid in the design of new interventional pharmacological and neuromodulation device treatments for addressing gastric motility disorders. Author SummaryThe coordinated contraction and relaxation of the muscles of the stomach, known as peristalsis is important for normal gastric motility and primarily governed by electrical depolarizations that originate and propagate within a network of interconnected layers of interstitial cells of Cajal (ICCs) and smooth muscle cells of the stomach wall as a slow-wave. Under normal conditions, a gastric slow-wave oscillates with a single period and uniform rostrocaudal lag, exhibiting network entrainment. However, the understanding of intrinsic and extrinsic mechanisms that ensure propagation of a robust entrained slow-wave remains incomplete. Here, using a computational framework, we show that in conjunction with an enteric neural stimulus gradient along the rostrocaudal ICC chain, and intercellular electrical coupling, the intercellular exchange of inositol trisphosphate between ICCs prevents decoupling by extending the longitudinal entrainment range along the stomach wall, even when variability in intercellular coupling exists. The findings from our study indicate ways that ensure the rostrocaudal spread of a robust gastric slow-wave and provide a mechanistic explanation for the emergence of decoupled slow waves associated with motility impairments of the stomach.

neuroscience↗

bioRxiv2020

Tactile active sensing in insect-plant pollination

The interaction between insects and the flowers they pollinate has driven the evolutionary diversity of both insects and flowering plants, two groups with the most numerous species on earth. Insects use vision and olfaction to localize their host plants, but to feed from the flower, they must find the tiny nectary opening, which can be well beyond their visual resolution. When vision is limited, the sense of touch becomes especially crucial, yet very few studies have investigated the role of rapid and precise tactile feedback in successful feeding and pollination interactions. In this paper, we study the remarkable feeding behavior of flying insects that use their proboscis, a flexible mouthpart often longer than their entire body length when unfurled, to expertly explore floral surfaces. Specifically, we observed how the crepuscular hawkmoth Manduca sexta interacts with artificial, 3D-printed flowers of varying shapes. We found that moths actively explore the flower for tactile features, systematically sweeping their proboscis from edge to center repeatedly until they locate the nectary. Moreover, naive moths rapidly learn to exploit flowers, and they adopt a tactile search strategy to more directly locate the nectary in as few as three to five consecutive visits. We suggest moths wield their proboscis to extract salient tactile features, such as floral edges and corolla curvature. Our results highlight the proboscis as a unique sensory structure and emphasize the central role of touch in insect-plant pollination interactions.

neuroscience↗

bioRxiv2019

Plasmodium knowlesi clinical isolates from Malaysia show extensive diversity and strong differential selection pressure at the merozoite surface protein 7D (MSP7D)

BackgroundHigh proportion of human cases due to the simian malaria parasite Plasmodium knowlesi in Malaysia has been a cause of concern, as it can be severe and fatal. Merozoite surface protein 7 (MSP7) is a multigene family which forms a non-covalent complex with MSP-1 prior to receptor-ligand recognition in Plasmodium falciparum and thus an important antigen for vaccine development. However, no study has been done in any of the ortholog family members in Plasmodium knowlesi from clinical samples. Thus in this study we investigated the level of polymorphism, haplotypes, and natural selection acting at the pkmsp-7D gene in clinical samples from Malaysia. MethodsWe analyzed 36 full-length pkmsp7D gene sequences (along with the reference H-strain: PKNH_1266000) which were orthologous to pvmsp7H (PVX_082680) from clinical isolates of Malaysia available from public databases. Population genetic, evolutionary and phylogenetic analyses were performed to determine the level of genetic diversity, polymorphism, recombination and natural selection. ResultsAnalysis of 36 full-length pkmsp7D sequences identified 147 SNPs (91 non-synonymous and 56 synonymous substitutions). Nucleotide diversity across the full-length gene was higher than its ortholog in P. vivax (msp7H). Region-wise analysis of the gene indicated that the nucleotide diversity at the central region was very high ({pi} = 0.14) compared to the 5 and 3 regions. Most hyper-variable SNPs were detected at the central domain. Multiple test for natural selection indicated the central region was under strong positive natural selection however, the 5 and 3 regions were under negative/purifying selection. Evidence of intragenic recombination were detected at the central region of the gene. Phylogenetic analysis using full-length msp7D genes indicated there was no geographical clustering of parasite population. ConclusionsHigh genetic diversity with hyper-variable SNPs and strong evidence of positive natural selection at the central region of MSP7D indicated exposure of the region to host immune pressure. Negative selection at the 5 and the 3 regions of MSP7D might be because of functional constraints at the unexposed regions during the merozoite invasion process of P. knowlesi. No evidence of geographical clustering among the clinical isolates from Malaysia indicated uniform selection pressure in all populations. These findings highlight the further evaluation of the regions and functional characterization of the protein as a potential blood stage vaccine candidate for P. knowlesi.

genetics↗