Biology subjects

Noblin, X.

Publications and source records attributed to Noblin, X..

6 recordsLinked to original sources

bioRxiv2026

Potassium modulates Phytophthora zoospore motility and flagellar beating through dose-dependent effects

Biflagellate zoospores are critical agents in the spread of Phytophthora spp., plant pathogens causing major agronomic and economic losses worldwide. These motile cells navigate soil water films toward plant roots using taxis triggered by environmental cues. Here, we investigate how potassium modulates zoospore motility by analyzing trajectory and flagellar beating parameters across KCl concentrations. Using high-speed imaging, we apply kymograph analysis and Fourier transform of the cell body direction over time to quantify flagellar dynamics, while low-speed imaging provides trajectory characteristics. Our results demonstrate that increasing potassium concentration significantly reduces swimming speed while enhancing directional changes. We establish a direct correlation between altered swimming speed and changes in flagellar beating parameters. Our findings indicate that potassium differentially affects anterior and posterior flagella beating. Furthermore, potassium exerts multiple effects, influencing beat amplitude, wave propagation speed and direction- change frequency. This reveals potassium as a key modulator of zoospore motility, triggering a shift from exploratory swimming to confined, reoriented movement. By uncovering the biomechanical responses of zoospores to potassium, this study advances our understanding of how surrounding signals regulate pathogen dispersal in the environment.

biophysics↗

bioRxiv2025

Membrane Proteome of Phytophthora parasitica Zoospores: How Does Sensing Occur?

Phytophthora plant pathogens rely on motile biflagellated zoospores to efficiently locate and colonise host tissues. While rhizospheric signals guiding zoospore movement toward roots are known, the protein composition of membranes mediating these responses remains unclear. Here, we used liquid chromatography with tandem mass spectrometry (LC-MS/MS) and proteomic data mining to analyse membrane fractions from the flagella and cell bodies of Phytophthora parasitica zoospores. Major classes of membrane proteins (receptors, transporters and enzymes) were identified and their subcellular distribution between flagella and cell bodies quantified. Immunolocalization revealed that while most membrane proteins are evenly distributed, a subset localizes to the flagella, suggestive of specialized roles in sensing and movement regulation, particularly for sterol recruitment and ion flux variations. These findings advance our understanding of protein-mediated dispersal and host targeting by zoospores and support the hypothesis that zoospores use polarized signal perception mechanisms for environmental sensing and movement.

microbiology↗

bioRxiv2024

Rapid microfluidic perfusion system enables controlling dynamics of intracellular pH regulated by Na+/H+ exchanger NHE1

pH regulation of eukaryotic cells is of crucial importance and influences different mechanisms including chemical kinetics, buffer effects, metabolic activity, membrane transport and cell shape parameters. In this study, we develop a microfluidic system to rapidly and precisely control a continuous flow of ionic chemical species to acutely challenge the intracellular pH regulation mechanisms and confront predictive models. We monitor the intracellular pH dynamics in real-time using pH-sensitive fluorescence imaging and establish a robust mathematical tool to translate the fluorescence signals to pH values. By varying flow rate across the cells and duration for rinsing process, we manage to tweak the dynamics of intracellular pH from a smooth recovery to either an overshooting state, where the pH goes excitedly to a maximum value before decreasing to a plateau, or an undershooting state where the pH is unable to recover to [~] 7. We believe our findings will provide more insight into intracellular regulatory mechanisms and promote the possibility of exploring cellular behavior in the presence of strong gradients or fast changes in homogeneous conditions.

bioengineering↗

bioRxiv2023

Kinetics of zoospores approaching a root using a microfluidic device

Phytophthora species are plant pathogens that cause considerable damage to agrosystems and ecosystems, and have a major impact on the economy. Infection occurs when their biflagellate zoospores move and reach a root on which they aggregate. However, the communication between the plant and the zoospores and how this communication modifies the behavior of the swimming zoospores is not yet well characterized. Here we show that using a microfluidic device comprising a growing Arabidopsis thaliana root, we are able to study the kinetics of Phytophthora parasitica zoospores approaching the root and aggregating on a specific area, in real time. We show that the kinetics of zoospores is modified only below a distance of about 300 m from the center of aggregation, with a decrease in the speed coupled with an increase in the number of turns made. In addition, we show that the rate of aggregation is constant throughout the experiment, approximately one hour, and depends on the density of zoospores. The rate is consistent with a random encounter of zoospores with the root, indicating that no long range signal is evidenced in our set-up.

biophysics↗

bioRxiv2021

Cooperation of two opposite flagella allows high-speed swimming and active turning in zoospore

Phytophthora species cause diseases in a large variety of plants and represent a serious agricultural threat, leading, every year, to multibillion dollar losses. Infection occurs when these biflagellated zoospores move across the soil at their characteristic high speed and reach the roots of a host plant. Despite the relevance of zoospore spreading in the epidemics of plant diseases, characteristics of individual swimming of zoospores have not been fully investigated. It remains unknown about the characteristics of two opposite beating flagella during translation and turning, and the roles of each flagellum on zoospore swimming. Here, combining experiments and modeling, we show how these two flagella contribute to generate thrust when beating together, and identify the mastigonemes-attached anterior flagellum as the main source of thrust. Furthermore, we find that turning involves a complex active process, in which the posterior flagellum temporarily stops, while the anterior flagellum keeps on beating and changes its pattern from sinusoidal waves to power and recovery strokes, similar to Chlamydomonass breaststroke, to reorient its body to a new direction. Our study is a fundamental step towards a better understanding of the spreading of plant pathogens motile forms, and shows that the motility pattern of these biflagellated zoospores represents a distinct eukaryotic version of the celebrated "run-and-tumble" motility class exhibited by peritrichous bacteria.

biophysics↗

bioRxiv2018

Guidance of zoospores by potassium gradient sensing mediates aggregation

Biflagellate zoospores of some phytopathogenic Phytophthora species spontaneously aggregate within few minutes in suspension. Depending on species auto-aggregate formation results from bioconvection or from a sequence bioconvection-positive chemotaxis. In this study, we show that P. parasitica zoospores may form aggregates upon application of a K+ gradient in particular geometric arrangements. Based on the use of macro- and microfluidic devices, in addition to time-lapse live imaging both in the vertical and horizontal planes, we defined (i) the spatiotemporal and concentration scale evolution within the gradient in correlation with (ii) cell distribution and (iii) metrics of zoospore motion (velocity, trajectory). The results indicated that K+-induced aggregates result from a single bi-phasic temporal sequence involving negative chemotaxis and then bioconvection in a K+ gradient concentration scale [0-17 mM]. Each K+-sensing cell undergoes a forward-to-backward movement within a threshold range of 1-4mM, thereby forming progressively a swarm. Once a critical population density is achieved zoospores form a plume which undergoes a downward migration leading to aggregate formation on the support surface. We discuss putative sources for K+ gradient generation in natural environment (zoospore population, microbiota, plant roots, soil particles), and implication for events preceding inoculum formation on host plant.

microbiology↗