Biology subjects

Wallner, E.-S.

Publications and source records attributed to Wallner, E.-S..

10 recordsLinked to original sources

bioRxiv2026

A developmentally scheduled inhibitory polarity circuit centers the stomatal pore

Symmetry in living systems often arises from coordinated asymmetries at smaller scales. The guard cells of stomata--bilaterally symmetric epidermal valves that mediate plant-atmosphere gas exchange--show coordinated asymmetries in pore placement and wall modification. Stomatal form and function are deeply conserved, yet molecular mechanisms defining coordinated cellular asymmetry are unknown. Here we show that pore position arises from a combination of pole avoidance and gradient centering in the membranes and wall dividing sister guard cells. Boundaries are established by spatiotemporal restriction of the receptor-like kinase MUSTACHES (MUS), which directs the disordered polarity protein OCTOPUS-LIKE2 (OPL2) to pore-forming regions. OPL2 peaks correspond to a focus of microtubules, and, from this position, the pore emerges. Experimental rewiring of the MUS-OPL2 polarity module profoundly impacts stomatal morphogenesis, eliminating, shifting, or even redirecting the pore to the opposite wall. These findings reveal a stomata-specific integration and elaboration of core polarity and centering programs, and challenge previous models of stomatal morphogenesis.

developmental biology↗

bioRxiv2026

PHOTOTROPIN-mediated blue light signaling orients the asymmetry of Marchantia polymorpha spores

Multicellular organisms produced by sexual reproduction develop from single cells and the asymmetry of these cells can define the orientation of the earliest developmental axes. The haploid multicellular stage of the plant, Marchantia polymorpha, develops from a single cell - the spore - that divides asymmetrically, producing an apical germ cell that generates the plant body and a smaller basal cell that differentiates as an anchoring germ rhizoid cell. We show that the orientation of this asymmetric cell division is controlled by an external, environmental cue - blue light - that is perceived by the photoreceptor PHOTOTROPIN and signals in an NCH1-dependent manner. This defines core elements of the mechanism by which a directional environmental signal orients cell division, which in turn orients the first axis of symmetry.

plant biology↗

bioRxiv2025

LysM Receptor Proteins are Required for Ectomycorrhizal Symbiosis in Poplar

Successful symbiotic associations often rely on the perception of specific microbial signals by host plants through pattern recognition receptors. LysM receptor-like kinases are key receptors in both rhizobial and arbuscular mycorrhizal symbioses. In this study, we provide the first evidence that such LysM receptor-like kinases also control the establishment of ectomycorrhizal associations in poplar. Using CRISPR/Cas9-mediated genome editing, we knocked out three NFP-like candidate genes in various combinations. We examined their roles in the perception of the ectomycorrhizal fungus Laccaria bicolor, as well as chitin oligomers and lipo-chitooligosaccharides. We demonstrate that all three receptors are necessary for the recognition of symbiosis-related signals, calcium spiking, symbiotic gene expression, and ectomycorrhizal root phenotypes.

plant biology↗

bioRxiv2025

De novo meristem development in Marchantia requires light and an apical auxin minimum

Meristems are generative centres with stem cells from which the bodies of land plants develop. Marchantia polymorpha spores are single cell structures formed at meiosis. On germination, spores divide asymmetrically to form a basal cell that terminally differentiates and an apical germ cell that divides into an early cell mass on which a flat prothallus develops. A single stem cell niche (meristem) forms de novo at the margin of the prothallus to drive development of the thallus plant body. Here we show that the prothallus forms at the apical pole of the early cell mass and represses the formation of other prothalli. LOW AUXIN RESPONSIVE (MpLAXR) marks this apical pole indicating that an auxin minimum is located at the site of organogenesis. Light is required for the formation of the apical auxin minimum and for the development of the prothallus from the early cell mass. Disrupting the apical auxin minimum by exogenous auxin treatment suppresses the transitions to the prothallus and formation of the meristem from the early cell mass. A similar molecular program operates during plant regeneration from a single differentiated thallus cell, which regains stemness (pluripotency) upon surgical isolation from surrounding tissues; the isolated cell divides forming an early cell mass that develops a local auxin minimum where a flat prothallus with a single meristem forms. We conclude that a light-dependent, apical auxin minimum is required for the formation of the prothallus and the de novo development of the first meristem in Marchantia polymorpha. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=199 SRC="FIGDIR/small/665278v2_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@c3c93org.highwire.dtl.DTLVardef@15d061borg.highwire.dtl.DTLVardef@3beacdorg.highwire.dtl.DTLVardef@1b45fd4_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2024

The three-dimensional anatomy and dorsoventral asymmetry of the mature Marchantia polymorpha meristem develops from a symmetrical gemma meristem

Meristems are three-dimensional generative structures that maintain a population of stem cells whilst producing new organs and tissues. Meristems develop in all land plants, however we know relatively little about the spatial and temporal regulation of meristem structure in lineages such as the bryophytes. Here we describe the three-dimensional anatomy of the meristem during the development of the liverwort, Marchantia polymorpha. Using optical reconstructions of the frontal, sagittal and transverse planes through the mature meristem, we show that the apical stem cell is sub-apical, ventral, and located in the outer cell layer. The anatomy of the mature meristem is therefore asymmetrical in the dorsoventral axis, which is reflected by the domain specific protein localisation of Marchantia Class III and Class IV Homeodomain-Leucine-Zippers (MpC3HDZ and MpC4HDZ) and promoter activity of MpYUCCA2. The dorsoventral asymmetry that defines the mature meristem is absent in the juvenile meristems of the asexual propagules known as gemmae. We discovered that anatomical dorsoventral asymmetry of the meristem forms after two days of gemmaling growth and is accompanied by expression of the dorsal identity reporter, MpC3HDZ. We conclude that the gemma meristem is in a state of arrested development and undergoes anatomical rearrangement to develop the three-dimensional meristem structure of the mature plant.

plant biology↗

bioRxiv2024

Reproducibly oriented cell divisions pattern the first flat body structures to set up dorsoventrality and de novo meristem formation in Marchantia polymorpha

Land plant bodies develop from stem cells located in meristems. However, we know little about how meristems initiate from non-meristematic cells. The haploid body of bryophytes develops from unicellular spores in isolation from the parental plant, which allows all stages of development to be observed. We discovered that the Marchantia spore undergoes a series of precisely oriented cell divisions to generate a flat prothallus on which a meristem later develops de novo. The young sporeling comprises an early cell mass. One cell of the early cell mass elongates and undergoes a formative division that produces the prothalloblast, which initiates prothallus formation. A symmetric division of the prothalloblast followed by two transverse divisions generate a four-celled plate that expands into a flat disc through oblique divisions in three of the four plate cell-derived quadrants. One quadrant gives rise to a flat flabellum. A notch with a meristem and apical stem cell develops at the margin of the flabellum. The transcription factor MpC3HDZ is a marker of the first flat prothallus structure and polarises to the dorsal tissues of flabella and meristems. Mpc3hdz mutants are defective in setting up dorsoventrality and thallus body flatness. We report how a regular set of cell divisions forms the prothallus - the first dorsoventral structure - and how cells on the margin of the prothallus develop a dorsoventralised meristem de novo.

plant biology↗

bioRxiv2023

Spatially resolved proteomics of the stomatal lineage: polarity complexes for cell divisions and stomatal pores

Cell polarity is used to guide asymmetric divisions and create morphologically diverse cells. We find that two oppositely oriented cortical polarity domains present during the asymmetric divisions in the Arabidopsis stomatal lineage are reconfigured into polar domains marking ventral (pore-forming) and outward facing domains of maturing stomatal guard cells. Proteins that define these opposing polarity domains were used as baits in miniTurboID-based proximity labeling. Among differentially enriched proteins we find kinases, putative microtubule-interacting proteins, polar SOSEKIs with their effector ANGUSTIFOLIA, and using AI-facilitated protein structure prediction models, we identify their potential interaction interfaces. Functional and localization analysis of polarity protein OPL2 and its newly discovered partners suggest a positive interaction with mitotic microtubules and a potential role in cytokinesis. This combination of cutting-edge proteomics and structural modeling with live cell imaging provides insights into how polarity is rewired in different cell types and cell cycle stages.

developmental biology↗

bioRxiv2020

Quantitative and dynamic cell polarity tracking in plant cells

Quantitative information on the spatiotemporal distribution of polarized proteins is central for understanding cell-fate determination, yet collecting sufficient data for statistical analysis is difficult to accomplish with manual measurements. Here we present POME, a semi-automated pipeline for the quantification of cell polarity, and demonstrate its application to a variety of developmental contexts. POME analysis reveals that during asymmetric cell divisions in the Arabidopsis thaliana stomatal lineage, polarity proteins BASL and BRXL2 are more asynchronous and less mutually dependent than previously thought. While their interaction is important to maintain their polar localization and recruit other effectors to regulate asymmetric cell divisions, BRXL2 polarization precedes that of BASL and can be initiated in BASLs absence. Uncoupling of polarization from BASL activity is also seen in Brachypodium distachyon, where we find that the MAPKKK BdYDA1 is segregated and polarized following asymmetric division. Our results demonstrate that POME is a versatile tool, which by itself or combined with tissue-level studies and advanced microscopy techniques can help uncover new mechanisms of cell polarity.

cell biology↗

bioRxiv2019

OBERON3 and SUPPRESSOR OF MAX2 1-LIKE proteins form a regulatory module specifying phloem identity

Spatial specificity of cell fate decisions is central for organismal development. The phloem tissue mediates long-distance transport of energy metabolites along plant bodies and is characterized by an exceptional degree of cellular specialization. How a phloem-specific developmental program is implemented is, however, unknown. Here we reveal that the ubiquitously expressed PHD-finger protein OBE3 forms a central module with the phloem- specific SMXL5 protein for establishing phloem identity in Arabidopsis thaliana. By protein interaction studies and phloem-specific ATAC-seq analyses, we show that OBE3 and SMXL5 proteins form a complex in nuclei of phloem stem cells where they establish a phloem-specific chromatin profile. This profile allows expression of OPS, BRX, BAM3, and CVP2 genes acting as mediators of phloem differentiation. Our findings demonstrate that OBE3/SMXL5 protein complexes establish nuclear features essential for determining phloem cell fate and highlight how a combination of ubiquitous and local regulators generate specificity of developmental decisions in plants.

plant biology↗

bioRxiv2019

SUPPRESSOR OF MAX2 1-LIKE 5 promotes secondary phloem formation during radial stem growth

As a prerequisite for constant growth, plants can produce vascular tissues at different sites in their postembryonic body. In particular, the formation of vascular tissues during longitudinal and radial expansion of growth axes differs fundamentally with respect to its anatomical configuration. This raises the question to which level regulatory mechanisms of vascular tissue formation are shared throughout plant development. Here, we show that, similar as primary phloem formation during longitudinal growth, the cambium-based formation of secondary phloem depends on the function of SMXL genes. Using promoter reporter lines, we observe that SMXL4 and SMXL5 activities are associated with different stages of secondary phloem formation in Arabidopsis stems and the specific loss of SMXL5 function results in the absence of secondary phloem. Interestingly, the additional disruption of SMXL4 activity increases cell proliferation rates in the cambium region without that secondary phloem is formed. Based on genome-wide transcriptional profiling and expression analyses of phloem-related markers we conclude that early steps of phloem formation are impaired in smxl4;smxl5 double mutants and that additional cambium-derived cells fail in establishing any phloem-related feature. Our results show that molecular mechanisms determining primary and secondary phloem share important features but differ slightly with SMXL5 playing a more dominant role in the formation of secondary phloem.

plant biology↗