Biology subjects

Dolan, L.

Publications and source records attributed to Dolan, L..

At least 19 recordsLinked to original sources

bioRxiv2026

RHO GTPase of Plants contributes to robust establishment of cellular asymmetry during development from a single cell

A fundamental question in developmental biology is how highly complex, yet reproducible multicellular body plans form from a single cell. The multicellular haploid body of the land plant Marchantia polymorpha develops from a single isolated cell - the spore - that divides asymmetrically. This produces a small terminally differentiating basal cell, and a large proliferative apical cell that gives rise to the multicellular sporeling body. The genetic basis for the establishment of asymmetry, first within the spore, and later within the sporeling body has remained virtually unknown. Here, we show that the plant specific RHO-type GTPase - RHO OF PLANTS (ROP) - polarises to the spore basal pole to ensure spore division is highly and reproducibly asymmetric. We demonstrate this highly asymmetric division is necessary to specify the terminal differentiation of the basal cell. Furthermore, we show that ROP-mediated polarised outgrowth is required to establish asymmetry within the sporeling body derived from the apical cell. Our discovery highlights how ROP function confers developmental robustness and contributes to the establishment of asymmetry during plant development from a single isolated cell.

plant 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

Antagonism between blue and red light-signalling controls thallus flatness in Marchantia polymorpha

The growth orientation of the Marchantia polymorpha thallus - a system of dorsiventralized, indeterminate axes - is modulated by light. We show that red and blue light act antagonistically to control thallus growth tropisms, with red light signalling promoting epinasty and blue light signalling promoting hyponasty. We found that loss-of-function mutations in the blue light receptor MpPHOT led to epinasty, while loss-of-function mutations in the red light receptor MpPHY resulted in hyponasty. We hypothesize that these antagonistic activities of blue and red light signalling are balanced in white light, resulting in the development of flat thalli. Using time-resolved transcriptomics, we identified genes that were rapidly induced upon light exposure. Among these genes were all six members of the M. polymorpha BBX gene family. Mutants harbouring loss-of-function mutations in two of the six MpBBX transcription factors developed defective thallus tropisms. Mpbbx1 loss-of-function mutants formed hyponastic thalli, while Mpbbx5 loss-of-function mutants developed epinastic thalli. Double mutants Mpbbx1 Mpbbx5 grew flat, supporting the hypothesis that they function antagonistically. Together, these data indicate that phototropin-mediated blue light and phytochrome-mediated red light signalling antagonistically modulate thallus tropism, and that BBX transcription factors also act antagonistically to regulate thallus flatness.

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↗

bioRxiv2025

Conservation and divergence of UVR8-COP1/SPA-HY5 signaling in UV-B responses of Marchantia polymorpha

Ultraviolet-B radiation (UV-B) poses a major challenge to all forms of plant life. The liverwort Marchantia polymorpha (Marchantia) serves as a key model organism to study signaling pathways and to infer their evolution throughout the green lineage. Marchantia expresses key components of UV-B signaling, including the photoreceptor UV RESISTANCE LOCUS 8 (MpUVR8), the WD40-repeat protein REPRESSOR OF UV-B PHOTOMORPHOGENESIS (MpRUP), the E3 ubiquitin ligase complex CONSTITUTIVELY PHOTOMORPHOGENIC 1 / SUPPRESSOR OF phyA-105 (MpCOP1/MpSPA), and the transcriptional regulator ELONGATED HYPOCOTYL 5 (MpHY5). Here, we show that MpUVR8 exists as a homodimer in its ground-state in vivo, then monomerizes and accumulates in the nucleus upon UV-B activation. Activated MpUVR8 interacts with MpCOP1, triggering growth inhibition, genome-wide gene expression changes, biosynthesis of UV-absorbing metabolites, and photoprotection, which overall contributes to UV-B stress tolerance. MpRUP facilitates redimerization of MpUVR8 and Mprup null mutants show enhanced UV-B photomorphogenesis, demonstrating that MpRUP efficiently represses MpUVR8 signaling. Unlike the case in Arabidopsis and in contrast to the strong Mpcop1 mutant phenotype, Mpspa mutants develop only a very weak constitutive photomorphogenesis phenotype, indicating that COP1 function is much more independent of SPA in Marchantia than in Arabidopsis. Moreover, in contrast to Arabidopsis SPAs, Mpspa is linked with a hyper-responsive UV-B phenotype, suggesting that MpSPA is a negative regulator of MpUVR8 signaling. Similar to Arabidopsis HY5/HYH, MpHY5 functions antagonistically to MpCOP1, but its role in UV-B-mediated gene expression changes is more limited. Our findings demonstrate that although core components of UV-B signaling existed in the last common ancestor of extant land plants, regulatory interactions have diversified in different lineages since their divergence more than 400 million years ago.

plant biology↗

bioRxiv2025

The cytochrome P450 enzyme MpCYP78E1 inhibits meristem initiation and activity in Marchantia polymorpha

Plant shoot branches are formed by the initiation and activation of generative centres known as meristems. In dichotomously branching plants, such as many bryophytes and lycophytes, new meristems are formed when a pre-existing meristem splits into two daughter meristems. These meristems may be active and produce shoot branches or may be inactive. Here, we show that in conditions where meristem inactivation occurs, such as simulated shade, the position of the inactive meristem alternated between either side of the plant body in the liverwort Marchantia polymorpha. Using this predictable pattern, we generated transcriptomes of active and inactive meristems and identified the cytochrome P450 monooxygenase, MpCYP78E1, as a novel regulator of meristem activity. MpCYP78E1 reporter expression was higher in active meristems than inactive meristems. More meristems were active in loss of function mutants than wild type, and fewer meristems were active in gain of function mutants, indicating that MpCYP78E1 inhibits meristem activity. Furthermore, unlike wild type, Mpcyp78e1 loss of function mutants produced supernumerary meristem from the centre of the mature plant body. We conclude that MpCYP78E1 inhibits both meristem initiation and activity to modulate shoot branching architecture.

plant biology↗

bioRxiv2025

Phytochrome A is required for light-inhibited germination of Aethionema arabicum seed

O_LIThe germination of most seeds is influenced by the duration, intensity, and quality of light. The seeds of the model plant Arabidopsis are positive photoblastic and require light to germinate. The germination of negative photoblastic seeds is inhibited by white light. The molecular mechanisms that regulate negative photoblastic germination are unknown due to the lack of a suitable model plant. C_LIO_LIWe identified an accession with negative photoblastic germination in Aethionema arabicum that grows in semi-arid natural habitats. In a forward genetic screen, we identified a mutant - koyash2 (koy2) - that is defective in negative photoblastic germination. There is a nonsense mutation in the gene encoding the phytochrome A photoreceptor in the koy2 mutant. C_LIO_LIHere we show that phytochrome A is required for negative photoblastic germination. The defective negative photoblastic phenotype of the koy2 mutant is the result of defective inhibition of germination by the phytochrome A mediated high-irradiance response. C_LIO_LIThis is the first example of phytochrome A-mediated response controlling negative photoblastic seed germination in white, red, far-red, and blue light. We speculate that genetically encoded variation in phytochrome A-mediated germination responses is responsible for local adaptation of Ae. arabicum throughout the Irano-Turanian region. C_LI One sentence summaryIdentification and characterization of a phytochrome A null mutant demonstrates an active role of phytochrome A in light-inhibited seed germination in Aethionema arabicum, a negative photoblastic Mediterranean plant.

plant biology↗

bioRxiv2024

Population genomics of Marchantia polymorpha subspecies ruderalis reveals evidence of climate adaptation

Sexual reproduction results in the development of haploid and diploid cell states during the life cycle. In bryophytes the dominant multicellular haploid phase produces motile sperm that swim through water to the egg to effect fertilization from which a relatively small diploid phase develops. In angiosperms, the reduced multicellular haploid phase produces non-motile sperm that is delivered to the egg through a pollen tube to effect fertilization from which the dominant diploid phase develops. These different life cycle characteristics are likely to impact the distribution of genetic variation among populations. However, little is known about the distribution of genetic variation among populations of bryophytes. To understand how genetic variation is distributed among populations of a bryophyte and to establish the foundation for population genetics research in bryophytes, we described the genetic diversity of collections of Marchantia polymorpha subspecies ruderalis, a cosmopolitan ruderal liverwort. We explored genetic diversity of this species using 78 genetically unique (non-clonal) accessions from a total of 209 collected from 37 sites in Europe and Japan. There was no detectable population structure among European populations but significant genetic differentiation between Japanese and European populations. By associating genetic variation across the genome with global climate data, we identified summer temperature and precipitation as climate factors influencing the frequency of adaptative alleles. We speculate that the requirement for water through which motile sperm swim imposes a constraint on the life cycle to which the plant genetically adapts.

plant 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↗

bioRxiv2024

The Immobilization of Hyaluronic Acid in 3D Hydrogel Scaffolds Modulates Macrophage Polarization

Macrophages are key modulators of immunity, tissue homeostasis and disease development. As our understanding of macrophage biology and their tissue specific behaviors grow the necessity to model macrophages within a 3D biomimetic environment becomes increasingly apparent. Numerous hydrogels have been developed and explored for this purpose, extracellular matrix (ECM) mimicking hydrogels gaining a special interest. In this study, we present the use of such a hydrogel composed of collagen and hyaluronic acid (HA), two of the major ECM components, for the 3D culture of macrophages to model their role in different tissues and diseases. We demonstrate the ability to tailor the mechanical properties of the hydrogel through formulation modulation. Human macrophages retain morphology, viability, and expression of key cell surface markers when 3D cultured within the hydrogel. Interestingly, we demonstrate in this work, that independent of mechanical properties, by adjusting the composition of the hydrogel, specifically HA molecular weight, we can steer macrophage polarization towards either a pro-inflammatory or anti-inflammatory phenotype. This HA-dependent modulation of macrophage behavior is nullified if the HA is chemically crosslinked, shedding light on the impact of one of the most commonly used preparation methods for collagen-HA hydrogels on macrophage behavior. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/588451v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@1cbe667org.highwire.dtl.DTLVardef@1837e58org.highwire.dtl.DTLVardef@1dbdbc6org.highwire.dtl.DTLVardef@139d65b_HPS_FORMAT_FIGEXP M_FIG C_FIG Hyaluronic acid (HA) is an extracellular matrix component, which can modulate the polarization of macrophages. The chemical crosslinking of HA to hydrogel scaffolds counteracts the cell signaling role of this molecule, preventing HA from modulating the immune polarization of macrophages within the model. Key pointsO_LICollagen-HA hydrogels form suitable biomimetic niches for the 3D culture of human macrophages in which hydrogel composition modulates macrophage phenotype, specifically the presence and molecular weight of HA. C_LIO_LIPolarization of macrophage phenotype by HA is nullified if HA is chemically cross-linked within the hydrogel. C_LI

bioengineering↗

bioRxiv2024

Microtubules and actin filaments direct nuclear movement during the polarisation of Marchantia spore cells

Multicellular organisms typically develop from single cells, the polarity of which establishes the first body axis of the organism. The multicellular haploid stage of land plants develops from a single haploid cell produced by meiosis - the spore. Starting from a non-polar state, these spores develop polarity and divide asymmetrically to establish the first apical-basal axis of the plant body. In the spore of the liverwort, Marchantia polymorpha, we show that the nucleus migrates from the cell centroid to the side of the cell to define the future basal pole. A microtubule organising centre leads this migration by initiating a dense microtubules array towards the cortex at the basal pole. Simultaneously, cortical microtubules disappear from the apical hemisphere but persist near the basal pole. A dense network of fine actin filaments also accumulates between the nucleus and the basal cell cortex. These data demonstrate that microtubules and actin filaments reorganise during the polarisation of the M. polymorpha spore. We speculate that signals orient microtubules and actin filaments during spore polarisation, resulting in the formation of a fine actin filament network between the nucleus and cell cortex that moves the nucleus to the future basal pole. SUMMARY STATEMENTMicrotubules and actin filament dynamics are required for the basal movement of the nucleus which establishes cell asymmetry before cell division in the Marchantia spore.

plant biology↗

bioRxiv2024

Long days induce adaptive secondary dormancy in seed of the Mediterranean plant Aethionema arabicum

Secondary dormancy is an adaptive trait that increases reproductive success by aligning seed germination with permissive conditions for seedling establishment. Aethionema arabicum is an annual plant and member of the Brassicaceae that grows in environments characterized by hot and dry summers. Aethionema arabicum seeds may germinate in early spring when seedling establishment is permissible. We demonstrate that long-day light regimes induce secondary dormancy in seed of Aethionema arabicum (CYP accession) repressing germination in summer when seedling establishment is riskier. Characterization of mutants screened for defective secondary dormancy demonstrated that RGL2 mediates repression of genes involved in GA signalling. Exposure to high temperature alleviates secondary dormancy, restoring germination potential. These data are consistent with the hypothesis that long-day-induced secondary dormancy and its alleviation by high temperatures, may be part of an adaptive response limiting germination to conditions permissive for seedling establishment in spring and autumn.

plant biology↗

bioRxiv2024

KATANIN-mediated microtubule severing is required for MTOC formation and function in Marchantia polymorpha

Microtubule organising centres (MTOCs) are sites of localised microtubule nucleation in eukaryotic cells. Regulation of microtubule dynamics often involves KATANIN (KTN); a microtubule severing enzyme which cuts microtubules to generate new negative ends leading to catastrophic depolymerisation. In Arabidopsis thaliana, KTN is required for the organisation of microtubules in the cell cortex, preprophase band, mitotic spindle and phragmoplast. However, as angiosperms lack MTOCs, the role of KTN in MTOC formation has yet to be studied in plants. Two unique MTOCs - the polar organisers - form on opposing sides of the prophase nucleus in liverworts. Here we show that KTN-mediated microtubule depolymerisation is required for the de novo formation of polar organisers in the liverwort, Marchantia polymorpha. In Mpktn mutants that lack KTN function, the formation, shape, number, and function of polar organisers is defective. This is in addition to defective microtubule organisation in the cell cortex, preprophase band, mitotic spindle, and phragmoplast. These data demonstrate that KTN-mediated microtubule dynamics are required for the formation of liverwort-specific MTOCs.

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↗

bioRxiv2023

Control of cell fate specification and patterning by an ancestral microRNA

The formation of an organized body requires the establishment and maintenance of cells with structural and functional distinctive characteristics. A central question in developmental biology is how changes in the regulation of genes drive cell specification and patterning1. microRNAs (miRNAs) are small non-coding RNAs that regulate development through mRNA cleavage and/or translational repression2. In plants, miRNAs regulate key aspects including growth, development, stem cell maintenance, vegetative phase change, leaf morphogenesis, floral organ formation and flowering time3. Biogenesis of plant miRNAs depends on the activity of DICER-LIKE 1 (DCL1), an RNase type III endonuclease that processes double stranded RNA to give rise to mature miRNAs 4. The genomes of todays flora contain at least one bona fide copy of DCL1 5,6. Using Marchantia polymorpha -a model bryophyte that allows comparative approaches to infer characteristics of the ancestral land plant-, we demonstrate that MpDCL1a is required for the biogenesis of miRNAs and uncovered a central role for miR166/Homeodomain Zipper Class III-regulated auxin synthesis in the specification of cell identity, patterning, meristem function, laminar expansion and the development of the body in the last common ancestor of extant land plants.

plant biology↗

bioRxiv2023

ATP binding cassette transporters and uridine diphosphate glycosyltransferases are ancient protein families that evolved roles in herbicide resistance through exaptation

ATP-binding cassette (ABC) transporters actively transport various substances across membranes, while uridine diphosphate (UDP) glycosyltransferases (UGTs) are proteins that catalyse the chemical modification of various organic compounds. Both of these protein superfamilies have been associated with conferring herbicide resistance in weeds. Little is known about the evolutionary history of these protein families in the Archaeplastida. To infer the evolutionary histories of these protein superfamilies, we compared protein sequences collected from 10 species which represent distinct lineages of the Archaeplastida - the lineage including glaucophyte algae, rhodophyte algae, chlorophyte algae and the streptophytes - and generated phylogenetic trees. We show that ABC transporters were present in the last common ancestor of the Archaeplastida which lived 1.6 billion years ago, and the major clades identified in extant plants were already present then. Conversely, we only identified UGTs in members of the streptophyte lineage, which suggests a loss of these proteins in earlier diverging Archaeplastida lineages or arrival of UGTs into a common ancestor of the streptophyte lineage through horizontal gene transfer from a non-Archaeplastida eukaryote lineage. We found that within the streptophyte lineage, most diversification of the UGT protein family occurred in the vascular lineage, with 17 of the 20 clades identified in extant plants present only in vascular plants. Based on our findings, we conclude that ABC transporters and UGTs are ancient protein families which diversified during Archaeplastida evolution, which may have evolved to for developmental functions as plants began to occupy new environmental niches and are now being selected to confer resistance to a diverse range of herbicides in weeds.

evolutionary biology↗

bioRxiv2023

ROP GTPase regulates polarised cell growth and cell division orientation during tissue development and organogenesis in Marchantia polymorpha

Cell polarity - broadly defined as the asymmetric distribution of cellular activities and or subcellular components within a cell - determines the geometry of cell growth and division during development. RHO GTPase proteins regulate the establishment of cell polarity and are conserved among eukaryotes. RHO Of Plant (ROP) proteins are a subgroup of RHO GTPases that are required for cellular morphogenesis in plants. However, how ROP proteins modulate the geometry of cell growth and division during the morphogenesis of plant tissues and organs is not well understood. To investigate how ROP proteins function during tissue development and organogenesis, we characterised the function of the single copy ROP gene of the liverwort Marchantia polymorpha. M. polymorpha develops morphologically complex three-dimensional tissues and organs exemplified by air chambers and gemmae, respectively. Mprop loss of function mutants form defective air chambers and gemmae, indicating ROP function is required for tissue development and organogenesis. During air chamber and gemma development in wild-type, the MpROP protein is enriched to sites of polarised growth at the cell surface and accumulates at the expanding cell plate of dividing cells. Consistent with these observations, polarised cell growth is lost, and cell divisions are misoriented in Mprop mutants. We propose that ROP regulates both polarised cell growth and cell division orientation in a coordinated manner to orchestrate tissue development and organogenesis in land plants.

plant biology↗