Biology subjects

Barbez, E.

Publications and source records attributed to Barbez, E..

7 recordsLinked to original sources

bioRxiv2026

The interactome of the receptor kinase THESEUS1 reveals how cell wall integrity is linked to hormone signalling in Arabidopsis

The receptor kinase THESEUS1 (THE1) activates responses to impairment of cell wall integrity (CWI). However, the interaction partners enabling THE1 to mediate the responses remain underexplored, impeding a mechanistic understanding of THE1. We produced a set of THE1 GFP fusion constructs in which THE1 is either wild type, mutated in its kinase domain, has a loss of function mutation in its ectodomain, or lacks the kinase or extracellular domain. We used these constructs to perform localization studies and immunoprecipitation liquid chromatography tandem mass spectrometry under control and stress conditions (isoxaben induced cell wall damage and sorbitol induced hyperosmotic stress) to identify the THE1 interactome. The interactome of THE1 changed in a context dependent manner, linking THE1 to known signaling components in CWI maintenance and phytohormone response (such as proton pumps, calcium pumps, other receptor kinases or cellulose synthesis regulators). Moreover, we identified novel interactors, associating THE1 with hitherto unexplored signaling pathways in response to CWI impairment. Our results also suggest that the THE1G37D protein (corresponding to the the1 1 allele) is retained in the endoplasmic reticulum, explaining its loss of function phenotype. The THE1 interactome and localization data provide the foundation to build a mechanistic understanding of THE1 mediated CWI maintenance.

plant biology↗

bioRxiv2026

ER-located Ca2+ ATPase ACA2 regulates Ca2+ cytoplasmic pool linked to root hair growth in Arabidopsis thaliana

Root hairs (RH) are excellent model systems for studying cell size and polarity since they elongate several hundred-fold their original size. Their tip growth is regulated by both intrinsic and environmental signals and is associated with the existence of a highly controlled cytoplasmic tip Ca{superscript 2} gradient, whose disruption impairs RH development. The molecular mechanisms underlying the Ca2+ homeostasis fine tuning and the Ca2+ organellar contributions to the cytoplasmic pool remain unclear. In the model plant Arabidopsis thaliana, many efflux routes are present, including those that employ Ca2+-pumps from the Autoinhibited Ca2+-ATPase (ACA) family. Here, we identified that the ER localized ACA2, and to a lower extent ACA7, are crucial ACAs required to control RH growth. By using genetically encoded Ca2+ biosensors we showed that Ca2+-dynamics are compromised in the aca2-2 mutant, having lower cytosolic Ca2+ concentration [Ca2+]cyt and growth rate, showing an altered homeostatic calcium setpoint compared to Col-0. Accordingly, the ACA2 mutation changed the dynamics of [Ca2+]cyt oscillations coupled to growth rate, inducing longer periods and more regular oscillations in the dominant high-frequency range (around 22 s), and slower oscillations (around 1 min) in the low-frequency range. Finally, expression of ACA2 with changes in four putative Ca2+ binding residues (ACA2{Delta}Ca2+) failed to rescue the RH growth phenotype in the aca2-2 mutant. Collectively, our findings indicate that ER-localized ACA2 and possibly ACA7 are crucial for modulating cytoplasmic Ca2+ signals, possibly composing a critical part of a negative feedback loop, and their absence leads to impairments in RH cell elongation.

plant biology↗

bioRxiv2026

Cell wall charge gates iron availability in plant roots

Plants acquire essential mineral nutrients from the soil, yet these elements must first traverse the extracellular matrix of the root before reaching the cell surface. How the physical properties of this extracellular compartment influence nutrient distribution and availability remains poorly understood. In plants, this extracellular matrix is formed by the cell wall, which carries a dynamically regulated negative charge that can change during development and in response to environmental cues. Here we demonstrate that cell wall charge functions as a tunable electrostatic gate that determines how iron is partitioned between retention and bioavailability. This decoupling between iron abundance and availability reveals a fundamental tradeoff imposed by extracellular electrostatics. A mechanistic diffusion-binding model shows that increasing wall charge inherently enhances iron sequestration while limiting its mobility at the cell surface. Genetic perturbation of pectin de-methylesterification validates this principle in vivo. Moreover, iron limitation itself triggers active remodeling of cell wall charge, dynamically shifting the balance toward increased iron accessibility. Together, these findings identify the plant cell wall as an active regulator of nutrient homeostasis rather than a passive barrier. By dynamically modulating extracellular electrostatics, roots control iron partitioning and bioavailability, uncovering a new physical layer of regulation in plant mineral nutrition. One-Sentence SummaryThe plant cell wall operates as a tunable electrostatic gate that buffers and releases iron through spatially and environmentally regulated charge dynamics.

plant biology↗

bioRxiv2025

A workflow for absolute apoplastic pH assessment during live cell imaging in plant roots.

Apoplastic pH is a key regulator of plant development and environmental responses, influencing processes such as cell expansion, nutrient uptake, and intercellular signaling. Accurate tools for measuring absolute pH values at high spatial resolution are therefore essential, yet limiting. Here, we present a novel calibration-based workflow for the in vivo quantification of absolute apoplastic pH using the fluorescent pH indicator HPTS. While HPTS has previously been used primarily to track relative pH changes, our novel methodology enables precise absolute pH measurement through a simplified calibration strategy and a tailor-made Fiji Plugin. This approach offers a non-invasive, reproducible tool for investigating absolute extracellular pH with high spatial resolution, expanding the methodological toolbox available to plant physiologists.

plant biology↗

bioRxiv2023

Pectin methylesterase activity is required for RALF1 peptide signalling output

The extracellular matrix plays an integrative role in cellular responses in plants, but its contribution to the signalling of extracellular ligands largely remains to be explored. RAPID ALKALINIZATION FACTORs (RALFs) are extracellular peptide hormones that play pivotal roles in various physiological processes. Here, we address a crucial connection between the de-methylesterification machinery of the cell wall component pectin and RALF1 activity. Pectin is a polysaccharide, contributing to the structural integrity of the cell wall. Our data illustrate that the pharmacological and genetic interference with PECTIN METHYL ESTERASEs (PMEs) abolishes RALF1-induced root growth repression. Our data suggest that positively charged RALF1 peptides bind negatively charged, de-methylesterified pectin with high avidity. We illustrate that the RALF1 association with de-methylesterified pectin is required for its FERONIA-dependent perception, contributing to the control of the extracellular matrix and the regulation of plasma membrane dynamics. Notably, this mode of action is independent of the FER-dependent extracellular matrix sensing mechanism provided by FER interaction with the Leucine-Rich Repeat Extensin (LRX) proteins. We propose that the methylation status of pectin acts as a contextualizing signalling scaffold for RALF peptides, linking extracellular matrix dynamics to peptide hormone-mediated responses.

plant biology↗

bioRxiv2019

Auxin-dependent xyloglucan remodelling defines differential tissue expansion in Arabidopsis thaliana

Size control is a fundamental question in biology, showing incremental complexity in case of plants whose cells possess a rigid cell wall. The phytohormone auxin is a vital growth regulator with central importance for differential growth control. Here we show that growth inducing and repressing auxin conditions correlate with reduced and enhanced complexity of extracellular xyloglucans, respectively. In agreement, genetic interference with xyloglucan complexity distinctly modulates auxin-dependent differential growth rates. Our work proposes that an auxin-dependent, spatially defined effect on xyloglucan structure and its effect on cell wall mechanics specify differential, gravitropic hypocotyl growth.

plant biology↗

bioRxiv2018

PILS6 is a temperature-sensitive regulator of nuclear auxin input and organ growth in Arabidopsis thaliana

Global warming is threatening plant productivity, because plant growth is highly sensitive to elevated temperatures. High temperature (HT) triggers the auxin biosynthesis-dependent growth in aerial tissues. On the other hand, the contribution of auxin to HT-induced root growth is currently under debate. Here we show that the putative intracellular auxin carrier PIN-LIKES 6 (PILS6) is a negative regulator of organ growth and that its abundance is highly sensitive to HT. PILS6 localises to the endoplasmic reticulum (ER) and limits the nuclear availability of auxin, consequently reducing the auxin signalling output. HT represses the transcription and protein abundance of PILS6 specifically in the root tip, which impacts on PILS6-dependent root organ growth rates. Accordingly, we hypothesize that PILS6 is part of a novel mechanism, linking HT to auxin responses in roots.

plant biology↗