Biology subjects

Bergmann, D. C.

Publications and source records attributed to Bergmann, D. C..

16 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↗

bioRxiv2025

Transcriptional targets of SPEECHLESS and FAMA control guard cell division and expansion in the late stomatal lineage

Plant tissue development often relies on the specification of cell type initials with stem cell-like properties. These later undergo differentiation, losing division potential and acquiring specific identities and functions. In the stomatal lineage, protodermal cells develop into guard cells (GCs) through the action of bHLH transcription factors (TFs) SPEECHLESS (SPCH), MUTE and FAMA. Existing models support that these regulators act sequentially, but recent evidence indicates that SPCH expression and function are retained in late stomatal cells. Here, we combine transcriptomic and genetic approaches to define SPCHs function during the late stomatal lineage. We show that relative levels and activities of SPCH and FAMA control GC division and expansion. Through cell type-specific TF induction and mRNA sequencing, we identify late-lineage targets of both TFs, and through genetic perturbation of these targets, we demonstrate that their precise temporal regulation is required for proper GC morphology and function. Our findings reveal a previously unrecognized role for SPCH in late stomatal development and support a revised model in which the functions of stomatal bHLHs are not strictly separated in time.

plant biology↗

bioRxiv2024

Multi-scale dynamics influence the division potential of stomatal lineage ground cells in Arabidopsis

During development, many precursor lineages are flexible, producing variable numbers and types of progeny cells. What factors determine whether a precursor cell differentiates or retains the capacity to divide? Here, we leverage the developmental flexibility of the stomatal lineage ground cell (SLGC) in Arabidopsis leaves as a model for how flexible decisions are regulated. Using a quantitative approach that combines long-term live imaging and statistical modeling, we discover that cell size is a strong predictor of SLGC behaviour: larger SLGCs divide less often than smaller cells. We propose that cell size is linked to division behaviour at multiple spatial scales. At the neighbourhood scale, cell size correlates with the strength of cell-cell signaling, which affects the rate at which SPEECHLESS (SPCH), a division-promoting transcription factor, is degraded. At the subcellular scale, cell size correlates with nuclear size, which modulates the concentration of SPCH in the nucleus. Our work shows how initial differences in SPCH levels are canalized by nuclear size and cell-cell signaling to inform the behaviour of a flexible cell type.

developmental biology↗

bioRxiv2022

Cortical polarity ensures its own asymmetric inheritance in the stomatal lineage to pattern the leaf surface

Asymmetric cell divisions (ACDs) specify differential cell fates across kingdoms. In metazoans, preferential inheritance of fate determinants into one daughter cell frequently depends on polarity-cytoskeleton interactions (1, 2). Despite the prevalence of ACDs during plant development, evidence for analogous mechanisms that segregate fate determinants during ACD remain elusive. Here, we describe a mechanism in the Arabidopsis thaliana leaf epidermis that ensures unequal inheritance of a fate-enforcing polarity domain during the creation of stomata, essential two-celled valves that mediate gas exchange between the plant and environment. Formation of a plasma membrane-associated polarity domain, defined by BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL), overrides default division patterns in stomatal precursors. The polarity domain exerts this control by constraining formation of the preprophase band of microtubules that mark the cortical division site and are a hallmark of plant mitosis. Experimentally uncoupling preprophase band establishment from the polarity domain results in aberrant polarity inheritance and subsequent fate errors. Mechanistically, our analyses of the interactions between microtubules and BASL in native and heterologous contexts revealed that the stomatal lineage polarity domain locally depletes cortical microtubules by altering microtubule stability. As the inherited cortical BASL crescent scaffolds a MAPK cascade to suppress progenitor identity in one daughter post-division, we propose that BASL-microtubule interactions represent a novel strategy to link cell identity to division orientation. Together, our data highlight how a common biological module, coupling the cytoskeleton to fate segregation via cell polarity, has been configured to accommodate the unique features of plant development.

cell biology↗

bioRxiv2022

Extracurricular roles and divergent regulation of FAMA in Brachypodium and Arabidopsis stomatal development

Stomata, cellular valves found on the surface of aerial plant tissues, present a paradigm for studying cell fate and patterning in plants. A highly conserved core set of related basic helix-loop-helix (bHLH) transcription factors (TFs) regulate aspects of stomatal cell identity in diverse species. We characterized BdFAMA in the temperate grass, Brachypodium distachyon, and found this late-acting TF was necessary and sufficient for specifying stomatal GC fate, and unexpectedly could also induce the recruitment of subsidiary cells in the absence of its paralogue, BdMUTE. The overlap in function is paralleled by an overlap in expression pattern and by unique regulatory relationships between BdMUTE and BdFAMA. To better appreciate the relationships among the Brachypodium stomatal bHLHs, we characterized the diversity of bHLH complexes through in vivo proteomics in developing leaves and found evidence for multiple shared interaction partners. The ability of BdFAMA to compensate for BdMUTE then prompted us to reexamine the roles of these paralogues in Arabidopsis. By testing genetic sufficiency within and across species, we found that, while BdFAMA and AtFAMA can rescue stomatal production in Arabidopsis fama and mute mutants, only AtFAMA can participate in the specification of Brassica-family-specific myrosin idioblasts. Taken together, our findings further our understanding of how the molecular framework of stomatal development has been reprogrammed across the monocot/dicot divide, as well as within the grasses, to produce distinct stomatal forms and patterns, and compel us to refine the current models of stomatal bHLH function and regulatory feedbacks amongst paralogues.

plant biology↗

bioRxiv2022

Opposite polarity programs regulate asymmetric subsidiary cell divisions in grasses

Grass stomata recruit lateral subsidiary cells (SCs), which are key to the unique stomatal morphology and the efficient plant-atmosphere gas exchange in grasses. Subsidiary mother cells (SMCs) strongly polarise before an asymmetric division forms a SC. Yet apart from a proximal polarity module that includes PANGLOSS1 (PAN1) and guides nuclear migration, little is known regarding the developmental processes that form SCs. Using the genetic model grass Brachypodium distachyon, we identified BdPOLAR, which forms a novel, distal polarity domain in SMCs that is reciprocal to the proximal PAN1 domain. Both polarity domains are required for the formative SC division yet exhibit distinct roles in regulating pre-mitotic nuclear migration and SMC division plane orientation, respectively. Nonetheless, the domains are linked as the proximal domain controls polarisation of the distal domain. In summary, we identified two opposing polarity domains that coordinate the SC division, a process crucial for grass stomatal physiology.

plant biology↗

bioRxiv2021

On the edge: Evolution of polarity protein BASL and the capacity for stomatal lineage asymmetric divisions

Asymmetric and oriented stem cell divisions enable the continued production of patterned tissues. The molecules that guide these divisions include several "polarity proteins" that are localized to discrete plasma membrane domains, are differentially inherited during asymmetric divisions, and whose scaffolding activities can guide division plane orientation and subsequent cell fates. In the stomatal lineages on the surfaces of plant leaves, asymmetric and oriented divisions create distinct cell types in physiologically optimized patterns. The polarity protein BASL is a major regulator of stomatal lineage division and cell fate asymmetries in Arabidopsis, but its role in the stomatal lineages of other plants is unclear. Here, using phylogenetic and functional assays, we demonstrate that BASL is a eudicot-specific polarity protein. Among dicots, divergence in BASLs roles may reflect some intrinsic protein differences, but more likely reflects previously unappreciated differences in how asymmetric cell divisions are employed for pattern formation in different species. This multi-species analysis therefore provides insight into the evolution of a unique polarity regulator and into the developmental choices available to cells as they build and pattern tissues. HIGHLIGHTSO_LIBASL is a eudicot-specific regulator of stomatal lineage asymmetric cell divisions C_LIO_LIBASL protein evolution includes stepwise addition of polarity domains to an ancestral MAPK-binding chassis C_LIO_LICellular quiescence and BASL-guided polarity generate proper stomatal spacing in tomato C_LIO_LICell size and fate asymmetries are uncoupled in the tomato stomatal lineage C_LI

plant biology↗

bioRxiv2020

Tuning of self-renewing capacity in theArabidopsis stomatal lineage by hormonaland nutrition regulation of asymmetric celldivisions

Asymmetric and self-renewing divisions build and pattern tissues. In the Arabidopsis thaliana stomatal lineage, asymmetric cell divisions, guided by polarly localized cortical proteins, generate the majority of cells on the leaf surface. These divisions can be fine-tuned by systemic and environmental signals to modify tissue development, but the molecular mechanisms by which plants incorporate such cues to regulate asymmetric divisions are largely unknown. In a screen for modulators of cell polarity and asymmetric divisions, we identified a mutation in CONSTITIUTIVE TRIPLE RESPONSE 1, a negative regulator of ethylene signaling. We subsequently revealed antagonistic impacts of ethylene and glucose signaling on the self-renewing capacity of stomatal lineage stem cells. Quantitative analysis of the impacts of these signaling systems on cell polarity and fate dynamics showed that developmental information may be encoded in both the spatial and temporal asymmetries of polarity proteins. Taken together, our results provide a framework for a mechanistic understanding of how systemic information such as nutritional status and environmental factors tune stem cell behavior in the stomatal lineage, ultimately enabling optimization of leaf size and cell-type composition.

plant 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↗

bioRxiv2020

Single-Cell Resolution of Lineage Trajectories in the Arabidopsis Stomatal Lineage and Developing Leaf

Dynamic cell states underlie flexible developmental programs, such as with the stomatal lineage of the Arabidopsis epidermis. Initial stages of the lineage feature asynchronous and indeterminate divisions modulated by environmental cues, enabling cell fate flexibility to generate the requisite density and pattern of stomata for a given environment. It remains unclear, however, how flexibility of cell fates is controlled. Here, we uncovered distinct models of cell state differentiation within Arabidopsis leaf tissue by leveraging single-cell transcriptomics and molecular genetics. Our findings resolved underlying heterogeneity within cell states of the flexible epidermal stomatal lineage, which appear to exist along a continuum, with progressive cell specification. Beyond the early stages of the lineage, we discovered that the core transcriptional regulator SPEECHLESS is required for cell fate commitment to yield stomatal guard cells. Overall, our work has refined the stomatal lineage paradigm and uncovered progressive cell state decisions along lineage trajectories in developing leaves.

plant biology↗

bioRxiv2019

Proximity labeling of protein complexes and cell type-specific organellar proteomes in Arabidopsis enabled by TurboID

Defining specific protein interactions and spatially or temporally restricted local proteomes improves our understanding of all cellular processes, but obtaining such data is challenging, especially for rare proteins, cell types, or events. Proximity labeling enables discovery of protein neighborhoods defining functional complexes and/or organellar protein compositions. Recent technological improvements, namely two highly active biotin ligase variants (TurboID and miniTurboID), allowed us to address two challenging questions in plants: (1) what are in vivo partners of a low abundant key developmental transcription factor and (2) what is the nuclear proteome of a rare cell type? Proteins identified with FAMA-TurboID include known interactors of this stomatal transcription factor and novel proteins that could facilitate its activator and repressor functions. Directing TurboID to stomatal nuclei enabled purification of cell type- and subcellular compartment-specific proteins. Broad tests of TurboID and miniTurboID in Arabidopsis and N. benthamiana and versatile vectors enable customization by plant researchers.

plant biology↗

bioRxiv2019

Stem-cell-ubiquitous genes spatiotemporally coordinate division through regulation of stem-cell-specific gene networks

Stem cells are responsible for generating all of the differentiated cells, tissues, and organs in a multicellular organism and, thus, play a crucial role in cell renewal, regeneration, and organization. A number of stem cell type-specific genes have a known role in stem cell maintenance, identity, and/or division. Yet, how genes expressed across different stem cell types, referred here as stem-cell-ubiquitous genes, contribute to stem cell regulation is less understood. Here, we find that, in the Arabidopsis root, a stem-cell-ubiquitous gene, TESMIN-LIKE CXC2 (TCX2), controls stem cell division by regulating stem cell-type specific networks. Development of a mathematical model of TCX2 expression allowed us to show that TCX2 orchestrates the coordinated division of different stem cell types. Our results highlight that genes expressed across different stem cell types ensure cross-communication among cells, allowing them to divide and develop harmonically together.

systems biology↗

bioRxiv2018

SOL1 and SOL2 Regulate Fate Transition and Cell Divisions in the Arabidopsis Stomatal Lineage

In the stomatal lineage, cells make fate transitions from asymmetrically dividing and self-renewing meristemoids, to commitment to the guard mother cell identity, and finally though a single division to create mature, post-mitotic stomatal guard cells. Flexibility in the stomatal lineage allows plants to alter leaf size and stomatal density in response to environmental conditions; however, transitions must be clean and unidirectional in order to produce functional and correctly patterned stomata. Among direct transcriptional targets of the stomatal initiating factor, SPEECHLESS, we found a pair of genes, SOL1 and SOL2, required for effective transitions in the lineage. Here we show that these two genes, which are homologues of the LIN54 DNA-binding components of the mammalian DREAM complex, are expressed in a cell cycle dependent manner and regulate cell fate and division properties in the self-renewing early lineage. In the terminal division of the stomatal lineage, however, these two proteins appear to act in opposition to their closest paralogue, TSO1, revealing complexity in the gene family may enable customization of cell divisions in coordination with development.

developmental biology↗

bioRxiv2018

Conservation and Divergence of YODA MAPKKK Function in Regulation of Grass Epidermal Patterning

All multicellular organisms must properly pattern cell types to generate functional tissues and organs. The organized and predictable cell lineages of the Brachypodium leaf enabled us to characterize the role of the MAPK kinase kinase gene BdYODA1 in regulating asymmetric cell divisions. We find that YODA genes promote normal stomatal spacing patterns in both Arabidopsis and Brachypodium, despite species-specific differences in those patterns. Using lineage tracing and cell fate markers, we show that, unexpectedly, patterning defects in bdyoda1 mutants do not arise from faulty physical asymmetry in cell divisions but rather from improper enforcement of alternative cellular fates after division. These cross-species comparisons allow us to refine our interpretations of MAPK activities during plant asymmetric cell divisions.\n\nSummary StatementAnalysis of Brachypodium leaf epidermis development reveals that the MAPKKK, BdYODA1, regulates asymmetric divisions by enforcing resultant cell fates rather than driving initial physical asymmetries.

plant biology↗

bioRxiv2017

Lineage and stage-specific expressed CYCD7;1 coordinates the single symmetric division that creates stomatal guard cells

Plants, with cells fixed in place by rigid walls, often utilize spatial and temporally distinct cell division programs to organize and maintain organs. This leads to the question of how developmental regulators interact with the cell cycle machinery to link cell division events with particular developmental trajectories. In Arabidopsis leaves, the development of stomata, two-celled epidermal valves that mediate plant-atmosphere gas exchange, relies on a series of oriented stem-cell-like asymmetric divisions followed by a single symmetric division. The stomatal lineage is embedded in a tissue whose cells transition from proliferation to post-mitotic differentiation earlier, necessitating stomatal lineage-specific factors to prolong competence to divide. We show that the D-type cyclin, CYCD7;1 is specifically expressed just prior to the symmetric guard-cell forming division, and that it is limiting for this division. Further, we find that CYCD7;1 is capable of promoting divisions in multiple contexts, likely through RBR-dependent promotion of the G1/S transition, but that CYCD7;1 is regulated at the transcriptional level by cell-type specific transcription factors that confine its expression to the appropriate developmental window.

plant biology↗

bioRxiv2017

Dissection of MAPK signaling specificity through protein engineering in a developmental context

Mitogen-activated protein kinases (MAPK) signaling affects many processes, some of which have different outcomes in the same cell. In Arabidopsis, activation of a MAPK cascade consisting of YODA, MKK4/5 and MPK3/6 inhibits early stages of stomatal developmental, but this ability is lost at the latest stage when guard mother cells (GMCs) transition to guard cells (GCs). Rather than downregulating cascade components, stomatal precursors must have a mechanism to prevent late stage inhibition because the same MKKs and MPKs mediate other physiological responses. Here, we artificially activated the MAPK cascade using MKK7, another MKK that can modulate stomatal development, and found that inhibition of stomatal development is still possible in GMCs. This suggests that MKK4/5, but not MKK7, are specifically prevented from inhibiting stomatal development. To identify regions of MKKs responsible for cell-type specific regulation, we used a domain swap approach with MKK7 and a battery of in vitro and in vivo kinase assays. We found that N-terminal regions of MKK5 and MKK7 establish specific signal-to-output connections like they do in other organisms, but they do so in combination with previously undescribed modules in the C-terminus. One of these modules encodes the GMC-specific regulation of MKK5, that when swapped with MKK7s, allows MKK5 to mediate robust inhibition of late stomatal development. Because MKK structure is conserved across species, the identification of new MKK specificity modules and signaling rules furthers our understanding of how eukaryotes create specificity in complex biological systems.

plant biology↗