Biology subjects

Hamann, T.

Publications and source records attributed to Hamann, T..

12 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

P2K1 P2K2 Coordinate Early, Structure-Specific Mechanical Adaptations to Osmotic and Cell Wall Stress in Arabidopsis Roots

The cell wall and plasma membrane (PM) form the interface between a plant cell and its environment yet how their mechanical properties change in response to stress is poorly understood. Here we investigate how the mechanical properties of the cell wall, plasma membrane, and vacuole change in vivo in Arabidopsis thaliana roots in response to hyperosmotic stress and cell wall damage (CWD) using a solvatochromic dye, molecular rotors, and Brillouin microscopy. We observe initially dynamic changes in mechanical properties of the PM that are sensitive to both hyperosmotic stress and CWD, while the cell wall changes are limited and the vacuole adapts only after several hours. In the p2k1 p2k2 double mutant, lacking receptors for extracellular ATP perception, sorbitol-induced effects on PM mechanostasis and early isoxaben-induced increases in PM order are lost. Our results indicate that P2K1 and P2K2 are required to modulate adaptive changes in mechanical properties of the PM induced by hyperosmotic stress and CWD.

plant biology↗

bioRxiv2026

Mechanisms underlying the defective development of xyloglucan-deficient root hairs in Arabidopsis thaliana

Hemicellulosic xyloglucan is abundant in the primary cell walls of eudicots and non-gramineous monocots and contributes to their mechanical integrity. Its deficiency results in morphologically abnormal root hairs in Arabidopsis mutants lacking either two XYLOGLUCAN XYLOSYLTRANSFERASE (xxt1 xxt2) or five CELLULOSE SYNTHASE-LIKE C (cslc-{triangleup}5) genes, but the cellular and biomechanical mechanisms underlying these abnormalities have remained unexplored. We combined multiple imaging modalities and quantitative modeling to unmask these mechanisms, first observing that xyloglucan-deficient mutants produced fewer and shorter root hairs that grew slower than wild type. Xyloglucan-deficient trichoblasts showed root hair initiation defects, helping to explain the sparseness of root hairs in these mutants. The mutant root hairs also had lower turgor pressure, thicker walls, and wider cross-sections, that explain lack of anisotropic growth, but cellulose organization appeared normal in xyloglucan-deficient root hairs. Brillouin microscopy suggested that xyloglucan-deficient root hairs were softer than wild-type root hairs. Finite element modeling of mutant root hairs predicted lower surface stress and growth rates, which were directly proportional to turgor pressure and inversely proportional to wall thickness. Stress patterns on models hint at potential mechanisms of bulging in xyloglucan-deficient root hairs. We propose that though cellulose orientation specifies the axis of cell expansion, it cannot enforce it without xyloglucan that interlinks microfibrils into a load-bearing network, identifying matrix-cellulose interaction as a distinct and necessary determinant of anisotropic plant cell growth.

cell biology↗

bioRxiv2026

Water stress adaptive responses in plants require movement of ABA and AB-aldehyde from vascular to target tissues

Vascular plants rapidly coordinate root and shoot responses to water stress. Abscisic acid (ABA) mediates these adaptations; however, it remains unclear which cells produce ABA, whether ABA synthesis shifts during stress, and whether ABA movement is required for its adaptive functions. Here, we map ABA biosynthesis at cellular resolution in Arabidopsis and report that water-stress adaptive responses in roots and shoots require movement of ABA and its precursor AB-aldehyde from vascular tissues to target cells. We suggest that ABA accumulation arises from two parallel routes: (i) ABA synthesized in the vasculature via ABA2 and AAO3, then moving to guard cells, and (ii) phloem-derived AB-aldehyde being converted to ABA in the epidermis or bundle sheath by AAO1 and AAO2. Finally, we predict that tightly packed cells beneath leaf veins facilitate efficient ABA delivery to guard cells, an anatomical arrangement that has enabled angiosperms to evolve the use of ABA to rapidly close stomata.

plant biology↗

bioRxiv2025

Coping with stress: Transcriptional regulators linking cell wall integrity maintenance with primary-wall metabolism in Arabidopsis thaliana

Cell wall damage (CWD) and hyperosmotic stress elicit both distinct and overlapping transcriptional programs in plants. Responses to these stresses involve cell wall integrity (CWI) maintenance, which is mediated by receptor-like kinases such as THESEUS1 (THE1), yet the downstream regulators linking early signalling to primary cell-wall metabolism and stress-induced phytohormone biosynthesis remain poorly defined. We induced CWD and hyperosmotic stress in wild type and the1 mutant alleles with isoxaben (ISX) and sorbitol, and analysed the gene expression of treated seedlings by RNA-seq. From these data, we focused on 15 transcriptional regulators whose expression was responsive to treatments and showed dependency on THE1 activity. Following up, we performed various functional analyses in mutant lines of these candidates and identified transcription factors that influence primary cell-wall metabolism, growth, transcriptional control of cellulose production, resistance to CWD and hyperosmotic stress, as well as phytohormone and lignin biosynthesis. Our results identify JMJ17, bHLH, and CBP60A as essential transcriptional regulators involved in responses to CWD and hyperosmotic stress, and they provide a starting point for dissecting the transcriptional network that regulates CWI maintenance and primary cell wall metabolism. This study sheds light on a previously unknown signalling network that regulates primary cell wall synthesis in control and stress conditions, providing a basis for more resilient crop plant breeding in the future. Significance StatementPlants provide food and materials used by society, and their productivity depends on maintaining cell wall integrity (CWI) during growth, development, and environmental stress. The CWI maintenance mechanism, involving receptor-like kinases such as THESEUS1 (THE1), has been extensively investigated, yet the transcriptional regulators involved in primary wall metabolism and stress-induced phytohormone production remain unknown. Here, we integrate transcriptomics with functional genetic and physiological assays to identify transcription factors acting in a THE1-dependent/independent manner. These regulators link CWI, hyperosmotic stress, and cell wall damage to primary wall metabolism, lignification, phytohormone production, and root growth. Our findings reveal elements of the transcriptional network that coordinate CWI and primary cell wall formation with adaptive responses, generating insights to enhance crop stress resilience.

plant biology↗

bioRxiv2025

Transgenerational polarity axis inheritance during Ceratopteris embryogenesis

For sexually reproducing organisms to pass on their genetic information, progeny must successfully establish. Various life history strategies have evolved, using either dispersal of large numbers of progeny or intensive nurturing of a few. Most plants use the former strategy, but ferns generate a single embryo in the exact same location as the mother, and it is unknown how progeny success is promoted, or how embryogenesis is adapted. By studying Ceratopteris richardii embryogenesis, we find that maternal tissues guide orientation of the early embryo body axis, thus aligning its root pole towards the homologous maternal rhizoids. We find that axis polarity inheritance is mediated by maternal tissue mechanical patterns, and thus identify a robust mechanism for progeny establishment as a nurturing strategy in plants.

plant biology↗

bioRxiv2025

The mechanical properties of Arabidopsis thaliana roots adapt dynamically during development and to stress

Mechanical properties of plant cells and tissues change dynamically, influencing plant growth, development, and interactions with the environment. Despite their central roles in plant life, current knowledge of how these properties change in vivo is very limited. Here we have combined Brillouin microscopy and molecular rotors to investigate stiffness, viscosity and porosity in living Arabidopsis thaliana seedling roots during differentiation and in response to stress and genetic manipulation. We found that mechanical properties change in a cell- and tissue-specific manner. The properties change dynamically during differentiation to support directional cell expansion. Cell-type-specific adaptations are induced within hours in response to stress or changes in cell wall metabolism. The findings form the foundation for future studies to characterize regulatory mechanisms linking biochemical signaling and mechanical properties.

plant biology↗

bioRxiv2021

THESEUS1 modulates cell wall stiffness and abscisic acid production in Arabidopsis thaliana

Plant cells can be distinguished from animal cells by their cell walls and high turgor pressure. Although changes in turgor and stiffness of cell walls seem coordinated, we know little about the mechanism responsible for coordination. Evidence has accumulated that plants, like yeast, have a dedicated cell wall integrity maintenance mechanism. This mechanism monitors the functional integrity of the wall and maintains it through adaptive responses when cell wall damage occurs during growth, development, and interactions with the environment. The adaptive responses include osmo-sensitive-induction of phytohormone production, defence responses as well as changes in cell wall composition and structure. Here, we investigate how the cell wall integrity maintenance mechanism coordinates changes in cell wall stiffness and turgor in Arabidopsis thaliana. We show that the production of abscisic acid (ABA), the phytohormone modulating turgor pressure and responses to drought, depends on the presence of a functional cell wall. We find that the cell wall integrity sensor THESEUS1 modulates mechanical properties of walls, turgor loss point and ABA biosynthesis. We identify RECEPTOR-LIKE PROTEIN 12 as a new component of cell wall integrity maintenance controlling cell wall damage-induced jasmonic acid production. Based on the results we propose that THE1 is responsible for coordinating changes in turgor pressure and cell wall stiffness. Significance statementPlants need to constantly adapt to a changing environment. This includes responses to biotic and abiotic stress. Key elements influencing the response to abiotic stress are the plant cell walls surrounding all cells and the phytohormone abscisic acid, which influences turgor pressure in plants. Turgor pressure in plant cells is much higher than in animal cells and a key driver of plant growth and development. Here we investigate the mechanism regulating cell wall stiffness and coordinating changes in stiffness and turgor. We characterize key elements of the mechanism and dissect its mode of action. This knowledge will enable us to pursue novel approaches to improve plant resistance to drought stress, which is crucial in a rapidly changing environment.

plant biology↗

bioRxiv2019

CRK2-mediated control of ROS production by phosphorylation of the RBOHD C-terminus in Arabidopsis

Reactive oxygen species (ROS) are important messengers in eukaryotic organisms and their production is tightly controlled. Active extracellular ROS production by NADPH oxidases in plants is triggered by receptor-like protein kinase (RLK)-dependent signaling networks. Here we show that the cysteine-rich RLK CRK2 kinase activity is required for plant growth and CRK2 exists in a preformed complex with the NADPH oxidase RBOHD in Arabidopsis. Functional CRK2 is required for the full elicitor-induced ROS burst and consequently the crk2 mutant is impaired in defense against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Our work demonstrates that CRK2 regulates plant innate immunity. We identified in vitro CRK2-dependent phosphorylation sites in the C-terminal region of RBOHD. Phosphorylation of S703 RBOHD is enhanced upon flg22 treatment and substitution of S703 with alanine reduced ROS production in Arabidopsis. Phylogenetic analysis suggests that phospho-sites in C-terminal region of RBOHD are conserved throughout the plant lineage and between animals and plants. We propose that regulation of NADPH oxidase activity by phosphorylation of the C-terminal region might be an ancient mechanism and that CRK2 is an important element in regulating MAMP-triggered ROS production. One-sentence summaryCRK2 associates with and activates RBOHD to trigger MAMP-induced ROS production and reveals a novel regulatory mechanism for plant NADPH oxidases through phosphorylation of the C-terminus.

plant biology↗

bioRxiv2019

Functional characterization of genes mediating cell wall metabolism and responses to plant cell wall integrity impairment

Plant cell walls participate in all plant-environment interactions. Maintaining cell wall integrity (CWI) during these interactions is essential. This realization led to increased interest in CWI and resulted in knowledge regarding early perception and signalling mechanisms active during CWI maintenance. By contrast, knowledge regarding processes mediating changes in cell wall metabolism upon CWI impairment is very limited. To identify genes involved and to investigate their contributions to the processes we selected 23 genes with altered expression in response to CWI impairment and characterized the impact of T-DNA insertions in these genes on cell wall composition using Fourier-Transform Infrared Spectroscopy (FTIR) in Arabidopsis thaliana seedlings. Insertions in 14 genes led to cell wall phenotypes detectable by FTIR. A detailed analysis of four genes found that their altered expression upon CWI impairment is dependent on THE1 activity, a key component of CWI maintenance. Phenotypic characterizations of insertion lines suggest that the four genes are required for particular aspects of CWI maintenance, cell wall composition or resistance to Plectosphaerella cucumerina infection in adult plants. Taken together, the results implicate the genes in responses to CWI impairment, cell wall metabolism and/or pathogen defence, thus identifying new molecular components and processes relevant for CWI maintenance.

plant biology↗

bioRxiv2018

Cellulose biosynthesis inhibition reduces cell cycle activity in a nitrate reductase- and cytokinin-dependent manner

O_LIDuring growth, development and defense, cell wall integrity needs to be coordinated with cell cycle activity. In Saccharomyces cerevisiae, coordination is mediated by the cell wall integrity maintenance mechanism. In plants, little is known how coordination is achieved.\nC_LIO_LIHere we investigated coordination between plant cell wall and cell cycle activity in Arabidopsis thaliana seedlings by studying the impact of cell wall damage (CWD, caused by cellulose biosynthesis inhibition) on cell cycle gene expression, growth, phytohormone (jasmonic acid, salicylic acid, cytokinins) and lignin accumulation.\nC_LIO_LIWe found root growth and cell cycle gene expression are reduced by CWD in an osmo-sensitive manner. trans-zeatin application suppressed the CWD effect on gene expression. Quantification of cytokinins revealed CWD-induced, osmo-sensitive changes in several cytokinins. Expression of CYTOKININ OXIDASE2/DEHYDROGENASE (CKX2) and CKX3, encoding cytokinin-degrading enzymes, was elevated in CWD-exposed seedlings. Genetic studies implicated NITRATE REDUCTASE1/2 (NIA1/2) in the response to CWD. In nia1/2 seedlings CWD induced neither expression of CKX2/3 and cell cycle genes nor accumulation of jasmonic acid, salicylic acid and lignin.\nC_LIO_LIThis suggests that CWD causes increased CKX2/3 expression through a NIA1/2-mediated process. Increased CKX expression seems to cause changes in cytokinin levels, leading to reduced cell cycle gene expression.\nC_LI

plant biology↗

bioRxiv2017

Pattern-Triggered Immunity And Cell Wall Integrity Maintenance Jointly Modulate Plant Stress Responses

Plant cells are surrounded by walls, which must often meet opposing functional requirements during plant growth and defense. The cells meet them by modifying wall structure and composition in a tightly controlled and adaptive manner. The modifications seem to be mediated by a dedicated cell wall integrity (CWI) maintenance mechanism. Currently the mode of action of the mechanism is not understood and it is unclear how its activity is coordinated with established plant defense signaling. We investigated responses to induced cell wall damage (CWD) impairing CWI and the underlying mechanism in Arabidopsis thaliana. Interestingly inhibitor- and enzyme-derived CWD induced similar, turgor-sensitive stress responses. Genetic analysis showed that the receptor-like kinase (RLK) FEI2 and the mechano-sensitive, plasma membrane-localized Ca2+- channel MCA1 function downstream of the THE1 RLK in CWD perception. Phenotypic clustering with 27 genotypes identified a core group of RLKs and ion channels, required for activation of CWD responses. By contrast, the responses were repressed by pattern-triggered immune (PTI) signaling components including PEPR1 and 2, the receptors for the immune signaling peptide AtPep1. Interestingly AtPep1 application repressed CWD-induced phytohormone accumulation in a PEPR1/2-dependent manner. These results suggest that PTI suppresses CWD-induced defense responses through elicitor peptide-mediated signaling during defense response activation. If PTI is impaired, the suppression of CWD-induced responses is alleviated, thus compensating for defective PTI.\n\nSignificance statementStress resistance and plant growth determine food crop yield and efficiency of bioenergy production from ligno-cellulosic biomass. Plant cell walls are essential elements of the biological processes, therefore functional integrity of the cell walls must be maintained throughout. Here we investigate the plant cell wall integrity maintenance mechanism. We characterize its mode of action, identify essential signaling components and show that the AtPep1 signaling peptide apparently coordinates pattern triggered immunity (PTI) and cell wall integrity maintenance in plants. These results suggest how PTI and cell wall modification coordinately regulate biotic stress responses with plants possibly compensating for PTI impairment through enhanced activation of stress responses regulated by the CWI maintenance mechanism.

plant biology↗