Biology subjects

Peaucelle, A.

Publications and source records attributed to Peaucelle, A..

9 recordsLinked to original sources

bioRxiv2025

Arabidopsis GALACTURONOSYLTRANSFERASE (GAUT) 1 synthesizes a homogalacturonan tightly bound to the cell wall and required for cell expansion

Arabidopsis GALACTURONOSYLTRANSFERASE1 (GAUT1) synthesizes homogalacturonan (HG), the most abundant pectin in growing plant cells. GAUT1 has the greatest in vitro enzyme activity of the six confirmed Arabidopsis HG biosynthetic GAUTs, but its biological activity remains elusive. Here we show that Arabidopsis GAUT1 homozygous mutants have a severe dwarfed seedling phenotype, survive several weeks as 2 to 3 mm seedlings, and have severely reduced shoot and root growth and hypocotyl epidermal, cortex and endodermal cell size. gaut1-1 pollen tubes are shorter than WT with increased bursting. Complementation of homozygous gaut1-1 with GAUT1 coding sequence driven by the GAUT1 promoter restored WT-like growth. The extreme dwarf phenotype of homozygous gaut1-1 seedlings precluded their use for detailed cell wall analysis, thus suspensions cultures were produced from callus generated from mutant and WT seedlings. Homozygous gaut1-1 suspension cells were smaller than WT with [~]30% reduced wall GalA content compared to WT. Sequential extraction of the walls with increasingly harsh solvents and sugar composition analysis revealed reduced GalA content in only the 4M KOH post-chlorite fraction, indicating that GAUT1-synthesized HG was held tightly in the wall by direct or indirect hydrogen bonding and/or oxidation-sensitive linkages. Treatment of wall fractions with endopolygalacturonase to hydrolyze HG and gel electrophoretic separation of hydrolysates exposed an HG-associated doublet band markedly downregulated in the homozygous gaut1-1 4M KOH post-chlorite fraction and to a lesser extent in 4M KOH and sodium chlorite fractions. NMR analysis identified the band as rhamnogalacturonan (RG)-II. Super resolution microscopy using anti-HG antibodies showed that, compared to WT, the homozygous gaut1-1 hypocotyl epidermal and callus cells had reduced content and length of HG nanofilaments, HG fibers associated with cell expansion in Arabidopsis. The results demonstrate that GAUT1-synthesized HG resides in a tightly-cell-wall-bound, RG-II-containing polymer required for HG nanofilament formation and seedling cell expansion.

plant biology↗

bioRxiv2024

A change in the cell wall status initiates the elimination of the nucellus in Arabidopsis

The evolution of the seed habit coincides with a change in the cell fate of the nucellus, the sporophytic tissue responsible for female meiosis. Seeds arose when the nucellus retained the female spores instead of releasing them in the environment. As a consequence, the nucellus was partially eliminated to accommodate the growth of the female gametophyte inside the sporophyte. With the evolution of angiosperm seeds, the process of nucellus elimination was requisitioned to allow the growth of the endosperm, the second fertilization product devoted to store nutrients. Cell elimination differs from most known cell death programs as it leads to the apparent dismantling of the cell wall. Here, we show that nucellus elimination in Arabidopsis is initiated by the lysis of the pectic polysaccharides in the cell wall. This process exposes other cell wall components to possible further degradation and precedes a cell death program that leads to nuclear DNA fragmentation. Both pathways are regulated by TRANSPARENT TESTA 16, a MADS-domain transcription factor that evolved with seed plants. Finally, the causal effect of cell wall modification on nucellus development is demonstrated by inhibiting pectin degradation, thus suggesting that a change in the cell wall status might have driven seed evolution.

plant biology↗

bioRxiv2023

Imaging the microscopic viscoelastic anisotropy in living cells

Maintaining and modulating the mechanical anisotropy is essential for biological processes. How this is achieved on the microscopic scale in living soft matter is however not always clear. Here we introduce Brillouin Light Scattering Anisotropy Microscopy (BLAM) for mapping the high-frequency viscoelastic anisotropy inside living cells. Following proof-of-principle experiments on muscle myofibers, we apply this to study two fundamental biological processes. In plant cell walls we show how a phase-transition driven switch between anisotropic-isotropic wall properties may lead to asymmetric growth. In mammalian cell nuclei we uncover a spatio-temporally oscillating elastic anisotropy correlated to chromatin condensation, with long range orientational correlations that may provide a dynamic framework for coordinating intra-nuclear processes. Our results highlight the direct and indirect role the high-frequency mechanics can play in providing dynamic structure that lead to the regulation of diverse fundamental processes in biological systems, and offer a means for studying these. BLAM should find diverse biomedical and material characterization applications.

biophysics↗

bioRxiv2022

Biochemical characterization of Pectin Methylesterase Inhibitor 3 from Arabidopsis thaliana

The Arabidopsis thaliana PECTIN METHYLESTERASE INHIBITOR 3 (PMEI3) gene is frequently used as a tool to manipulate PME activity in vivo, in studies assessing the role of pectin de-methylesterification in the control of cell expansion. One limitation of these studies is that the exact biochemical activity of this protein has not yet been determined. In this manuscript we produced the protein in Pichia pastoris and characterized its activity in vitro. Like other PMEIs, PMEI3 inhibits PME activity in acidic pH conditions for a variety of cell wall extracts and for purified PME preparations, but doesnt affect PME activity at neutral pH. This suggests that the previously observed in vivo effects reflect the inhibition of PME activity at low pH. The protein is remarkable heat stable and shows higher activity against PME3 than against PME2, illustrating how different members of the large PMEI family can differ in their specificities towards PME targets. Finally, application of purified PMEI3 on Arabidopsis thaliana seedlings showed a dose-dependent inhibition of homogalacturonan de-methylesterification and root growth. Purified recombinant PMEI3 is therefore a powerful tool to study the connection between pectin methylesterification and cell expansion.

plant biology↗

bioRxiv2022

Spatiotemporal growth pattern during plant nutation implies fast dynamics for cell wall mechanics and chemistry: a multiscale study in Averrhoa carambola

Nutation is the most striking and ubiquitous example of the rhythmic nature of plant development. Although there is a consensus that this wide oscillatory motion is driven by growth, its internal mechanisms have not been fully elucidated yet. In this work, we study the specific case of nutation in compound leaves in the archetypal Averrhoa carambola plant. We quantify the macroscopic growth kinematics with time lapse imaging, image analysis and kinematics modeling. We further characterize the mechanical and chemical properties of the cell wall with atomic force microscopy and immunolabelling. Our data first reveal that the differential growth driving nutation is localized and peaks where the average growth drops. We then show this specific spatiotemporal growth profile is compatible with local contraction events. At the cell wall level, differential growth is further colocalized with an asymmetry of the cell wall elastic modulus, and with an asymmetric distribution of homogalacturonans (HG). Our results not only back up the hypothesis of HG being involved in plant growth, but also build up on it by suggesting a dynamic nature for this process. Significance StatementNutation is an oscillatory motion displayed by many organs of growing plants. Most works on nutation focus on its relation to external stimuli attempting to explain its origins. By contrast, its internal physiological mechanisms remain to be fully explored. Here we propose an experimental and multiscale characterization of undisturbed nutation. We determine the macroscopic growth profile and show it is compatible with cell expansion but also local contractions in the tissues. At the microscopic level, we reveal that both the rigidity and composition of the cell wall are asymmetrically distributed where nutation occurs. The combination of results on both scales brings contributions to the understanding of interplay between global movement, local growth, cell wall mechanics and cell wall biochemistry.

biophysics↗

bioRxiv2021

A cell wall-associated gene network shapes leaf boundary domains

Boundary domains delimit and organize organ growth throughout plant development almost relentlessly building plant architecture and morphogenesis. Boundary domains display reduced growth and orchestrate development of adjacent tissues in a non-cell autonomous manner. How these two functions are achieved remains elusive despite the identification of several boundary-specific genes. Here, we show using morphometrics at the organ and cellular levels that leaf boundary domain development requires SPINDLY (SPY), an O-fucosyltransferase, to act as cell growth repressor. Further we show that SPY acts redundantly with the CUP-SHAPED COTYLEDON transcription factors (CUC2 and CUC3), which are major determinants of boundaries development. Accordingly at the molecular level, CUC2 and SPY repress a common set of genes involved in cell wall loosening providing a molecular framework for the growth repression associated with boundary domains. Atomic force microscopy (AFM) confirmed that young leaf boundary domain cells have stiffer cell walls than marginal outgrowth. This differential cell wall stiffness was reduced in spy mutant. Taken together our data reveal a concealed CUC2 cell wall associated gene network linking tissue patterning with cell growth and mechanics. Summary statementDecreased cell-wall loosening gene expression contributes to the coordination of cell growth and mechanics with tissue patterning thus driving boundary development.

plant biology↗

bioRxiv2020

Expansin-controlled cell wall stiffness regulates root growth in Arabidopsis

Expansins facilitate cell expansion via mediating pH-dependent cell wall (CW) loosening. However, the role of expansins in the control of biomechanical CW properties in the tissue and organ context remains elusive. We determined hormonal responsiveness and specificity of expression and localization of expansins predicted to be direct targets of cytokinin signalling. We found EXPA1 homogenously distributed throughout the CW of columella/ lateral root cap, while EXPA10 and EXPA14 localized predominantly at the three-cell boundaries of epidermis/cortex in various root zones. Cell type-specific localization of EXPA15 overlaps with higher CW stiffness measured via Brillouin light scattering microscopy. As indicated by both Brillouin frequency shift and AFM-measured Youngs modulus, EXPA1 overexpression upregulated CW stiffness, associated with shortening of the root apical meristem and root growth arrest. We propose that root growth in Arabidopsis requires delicate orchestration of biomechanical CW properties via tight regulation of various expansins localization to specific cell types and extracellular domains.

plant biology↗

bioRxiv2020

Hook Shape of Growing Leaves Results from an Active Regulation

The rachis of most growing compound leaves observed in nature exhibit a stereotyped hook shape. In this study, we focus on the canonical case of Averrhoa carambola. Combining kinematics and mechanical investigation, we characterize this hook shape and shed light on its establishment and maintenance. We show quantitatively that the hook shape is a conserved bent zone propagating at constant velocity and constant distance from the apex throughout development. A simple mechanical test first reveals non-zero spontaneous curvature profiles for the growing leaves, indicating that the hook shape is actively regulated. It then evidences the robust spatial organization of growth, curvature, rigidity and lignification and their interplay. Regulation processes appear to be specifically localized: in particular, differential growth occurs where the elongation rate drops. Finally, impairing the graviception of the leaf on a clinostat led to reduced hook curvatures but not to its loss. Altogether our results suggest a role for proprioception in the regulation of the apical hook, likely mediated via mechanical strain.

plant biology↗

bioRxiv2019

ELIMAKI locus is required for mechanosensing and proprioception in birch trees

The remarkable vertical and radial growth observed in tree species, encompasses a major physical challenge for wood forming tissues. To compensate with increasing size and weight, cambium-derived radial growth increases the stem width, thereby supporting the aerial body of trees. This feedback appears to be part of a so-called \"proprioception\" (1, 2) mechanism that controls plant size and biomass allocation. Yet, how trees experience or respond to mechanical stress derived from their own vertical loading, remains unknown. Here, we combined two strategies to dissect the proprioceptive response in birch. First, we show that in response to physical loading, trees promote radial growth with different magnitudes along the stem. Next, we identified a mutant cultivar (B. pubescens cv. Elimaki) in which the main stem shows normal vertical development, but collapses after three months. By inducing precocious flowering, we generated a backcrossed population (BC1) by producing two generations in 4 years. In his scheme, we uncovered a recessive trait (eki) that segregates and genetically maps with a Mendelian monogenic pattern. Unlike WT, eki is resistant to vertical mechanical stimulation. However, eki responds normally to the gravitropic stimulus by making tension wood. Before the collapse, cell size in eki is compromised resulting in radial growth defects, depending on stem height. Cell walls of developing xylem and phloem tissues have delayed differentiation in eki, and its tissues are softer compared to WT as indicated by atomic force microscopy (AFM). The transcriptomic profile of eki highlighted the overlap with that of the Arabidopsis response to touch. Taken together, our results suggest that the mechanical environment and cell wall properties of developing woody tissues, can significantly affect the growth responses to vertical loading thereby compromising their proprioceptive capacity. Additionally, we introduce a fast forward genetics strategy to dissect complex phenotypes in trees.

plant biology↗