Meet the speakers

Meet the invited speakers taking part in the Sainsbury Laboratory Symposium. This page features speaker talk abstracts and links to laboratory websites and social media channels, making it easy to learn more about each speaker and their research.

Keynote speakers

Molecular and cellular basis of stem cell fate decision in the vascular cambium 

Vascular cambium produces secondary xylem inwards and secondary phloem outwards. Our earlier studies revealed that both xylem and phloem originate from a single bifacial stem cell. We recently identified transcription factors, that we named CAMBIUM-EXPRESSED AINTEGUMENTA-LIKEs (CAILs), as the long-sought stem cell factors of cambium. CAIL expression is promoted by auxin-induced, plasma membrane (PM) localized receptor kinase PXY, which is expressed broadly in developing xylem and weakly in the stem cell of cambium. We discovered that because PXY binds to the phloem-originated and apoplastically diffusible ligand, TDIF, it can effectively sequester further ligand diffusion into the apoplast of xylem. As a result, active TDIF-PXY complexes form within a narrow domain, where they activate CAIL expression, thereby maintaining stem cell identity. Overall, we showed how cambium stem cells are defined at the intersection of two opposing gradients: auxin-induced PXY receptor and phloem-originated TDIF ligand gradients. During the meeting, I will present unpublished data demonstrating the molecular and subcellular mechanism by which PXY sequesters TDIF, thereby preventing its diffusion into deeper xylem tissues. 

Transcription in plants

Invited speakers

Mechanisms at tricellular adherens junctions in epithelial morphogenesis 

In animal embryos, epithelial sheets dramatically change their shapes, such as during gastrulation or organogenesis. Epithelial sheet plasticity requires individual cells to remodel their cell-cell contacts while they exchange positions, divide or leave the epithelium. Cell-cell contact remodelling requires the activity of the cytoskeleton and associated membrane proteins and is primarily studied at epithelial bicellular junctions, both in vivo and in cultured cells. But epithelial cells also form contacts with more than one cell, at tricellular junctions, where three neighbouring cells attach at their corners. Compared to bicellular junctions, however, how tricellular junctions remodel and by which mechanisms they contribute to morphogenesis, is poorly understood.  

Specialised components at tricellular junctions have been identified but their functions in epithelial morphogenesis remain unclear. In Drosophila, we have discovered a new component of tricellular junctions, the transmembrane adhesion molecule Sidekick. Sidekick concentrates at tricellular adherens junctions in fly epithelia and is required for polarised cell rearrangements in developing tissues. We are using Sidekick as a molecular entry point to i) elucidate the organisation of cytoskeletal and membrane proteins at tricellular adherens junctions at the nanometre scale, using super-resolution microscopy (PAINT) in the intact embryo and ii) solve the mechanisms by which tricellular junctions control dynamics during cell rearrangements and other cell behaviours. We will present an update of our work.  

References

Lye CM, Naylor HW, Sanson B. Subcellular localisations of the CPTI collection of YFP-tagged proteins in Drosophila embryos. Development. 2014. PMID: 25294944. 

Finegan TM, Hervieux N, Nestor-Bergmann A, Fletcher AG, Blanchard GB, Sanson B. The tricellular vertex-specific adhesion molecule Sidekick facilitates polarised cell intercalation during Drosophila axis extension. PLoS Biol. 2019. PMID: 31805038. 

Nestor-Bergmann A, Blanchard GB, Hervieux N, Fletcher AG, Étienne J, Sanson B. Adhesion-regulated junction slippage controls cell intercalation dynamics in an Apposed-Cortex Adhesion Model. PLoS Comput. Biol. 2022. PMID: 35089922.

Stabilizing Cell Fate in Regeneration: A Feedback Perspective 

How do living systems rebuild themselves after disruption? In multicellular organisms, identity and growth are normally coordinated with exquisite precision across space and time. Wounding shatters this order: cell identities destabilize, polarity collapses, and tissues become disconnected. Yet, organisms restore structure and function with remarkable fidelity. This demands the integration of biochemical signals, mechanical forces, and geometry. How such integration gives rise to coherent form remains a fundamental open question. Plants serve as an effective model for addressing this question. They can regenerate entire organisms from just a few cells, often from almost any tissue. Because plant cells are immobilized by rigid cell walls, regeneration cannot rely on cell migration or recruitment. Instead, it emerges from local reprogramming guided by positional information. We combine molecular genetics, biochemistry, genomics, live imaging, and computational modeling to uncover how cells integrate biochemical, mechanical, and geometric inputs to make decisions, stabilize identity, and rebuild form. I will present how these interactions give rise to robust, self-organizing regenerative systems, revealing general principles of how plants restore order from disruption. 

Environmental and Hormonal Control of Epidermal Stem Cell Differentiation

A multiscale approach to understanding cell division orientation in plant morphogenesis 

Plant morphogenesis relies on the precise spatial orientation of cell division, as cell migration and programmed cell death are largely absent in young plant tissues. The establishment of the division plane is critical for tissue architecture and organ shaping, yet the mechanisms underlying division orientation—particularly in a multicellular context—remain poorly understood. While cell-autonomous cues have been extensively studied, the integration of tissue-scale mechanical stress and local environmental signals into division plane positioning is an emerging frontier. 

Our work focuses on elucidating how plant cells orient their division by integrating biophysical and biochemical signals from their surroundings. Using a multidisciplinary approach combining cell biology, molecular genetics, and mechanical modeling, we aim to address key questions:

• How does a dividing cell integrate with its local neighborhood to orient the division plane? 
• What molecular cues form the "compass" that incorporates mechanical and geometrical features to guide division orientation? 
• What is the role of maintaining division orientation at the organ scale, and how does this contribute to robust morphogenesis?

We have identified the actin cytoskeleton as a central regulator of division orientation in Arabidopsis thaliana. Actin dynamics enable cells to integrate positional information, sometimes overriding default geometric cues. Disruption of actin leads to misalignment between early cortical markers and final division outcomes, highlighting its role in stabilizing spindle orientation, particularly at apicobasal domains. Our findings suggest that actin-mediated regulation allows flexible implementation of a shared core strategy, favoring division perpendicular to the growth axis and symmetric partitioning, while avoiding lateral wall anchoring. 

Collectively, our current work will eventually provide a mechanistic, multiscale understanding of cell division positioning in plants, bridging the gap between local environmental cues and tissue-level morphogenesis.

Interaction between abscisic acid and key shoot apical meristem regulators plays a major role in meristem homeostasis

Plants sustain continuous organ formation throughout their life cycle due to the activity of stem cell-containing structures known as meristems. The shoot apical meristem (SAM) gives rise to all aerial organs, including leaves, stems, and flowers. Proper SAM function is therefore essential not only for maintaining shoot growth and plant architecture but also for determining reproductive output and overall crop yield. Understanding the molecular mechanisms that underlie SAM regulation is thus crucial from both developmental and agronomic perspectives.

SAM function relies on a precise balance between stem cell proliferation and differentiation, regulated by a network of genetic and hormonal factors. Key regulator genes such as CLAVATA3 (CLV3), WUSCHEL (WUS), and SHOOT MERISTEMLESS (STM) maintain the stem cell niche, while the hormones auxin and cytokinin (CK) coordinate organ initiation and cell proliferation, respectively. Despite extensive characterization of these regulatory pathways, the role of other hormones, such as abscisic acid (ABA), in the control of SAM homeostasis remains less well understood.

We have characterized the dynamics of ABA signaling in the SAM under normal developmental conditions and following the application of ABA or an ABA antagonist using high-resolution live imaging techniques. Additionally, we have monitored the expression of SAM function-related markers (e.g., CLV3, WUS, STM, CK response, and cell division markers) during ABA treatments or upon induction of ABA biosynthetic or catabolic genes in specific domains in the SAM. Changes in SAM size and organ production rate were also analysed after ABA level alterations and in mutants related to ABA pathways.

Our results indicate that ABA could promote CLV3 expression and repress WUS and STM expression, CK response, and cell divisions to prevent excessive stem cell proliferation in the center of the SAM and maintain a stable stem cell niche. Likewise, ABA could inhibit cell differentiation and the formation of primordia boundaries in the SAM.

Molecular Regulation of Root Growth under High Soil Mechanical Resistance

Shaping the hook: How mechanochemical signalling controls growth patterning

Plant morphogenesis depends on coordinated growth. The apical hook, a curved structure that protects the seedling during emergence, forms through differential cell elongation. Using imaging and modelling, we show that opposing growth gradients and cuticle integrity are key to maintaining hook curvature. Mechanical cues and reactive oxygen species (ROS) work together to regulate growth, linking physical and biochemical signals in organ shaping. 

Roads to complexity:  The making of plant vascular tissues

Vascular tissue formation is crucial for plant growth, enabling water, sugar and nutrient transport through transporting elements, derived from cambium stem cells (CSCs). CSCs produce vascular cell types in a bidirectional manner, but their regulation and cell fate trajectories remain unclear. In our lab we explore the role of SUPPRESSOR OF MAX2 1-LIKE (SMXL) proteins in determining vascular cell fates and in integrating external cues like water availability in respective developmental programs. In aprticular, we show that the phloem fate determinant protein SMXL5 functions as a chromatin-associated transcriptional repressor that constrains downstream developmental competence during early phloem formation. Ou results suggest that SMXL5 stabilizes phloem identity by constraining auxin-related transcriptional programs during early phloem development and highlight repression-mediated control of regulatory competence as a key mechanism supporting developmental robustness and preventing inappropriate fate transitions.

Divide, expand, open: How coordinated growth drives cotyledon development

Vishwadeep Mane (1, 2, 3), Constance Le Gloanec (3, 4), Daniel Kierzkowski (3), Yuchen Long (4), Christophe Godin (2), Olivier Hamant (2), Utpal Nath (1) 

(1) Department of Microbiology and Cell Biology (MCB), Indian Institute of Science (IISc), Bengaluru-560012, Karnataka, India. utpalnath@iisc.ac.in 

(2) Laboratoire de Reproduction et Développement des Plantes (RDP), Université de Lyon, Université Claude Bernard Lyon 1 (UCBL), ENS de Lyon, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), CNRS, 69364 Lyon Cedex 07, France. 

(3) Institut de Recherche en Biologie Végétale (IRBV), Département de Sciences Biologiques, Université de Montréal (UdeM), Montréal, Québec, H1X 2B2, Canada. 

(4) Department of Biological Sciences, National University of Singapore (NUS), Singapore 117543, Singapore 

Developmental robustness ensures consistent organ shape and size despite genetic and environmental variation. In Arabidopsis cotyledons, the transition from embryonic proliferation to post-germination differentiation is thought to determine final morphology, yet its cellular basis during seed germination remains unclear, primarily due to technical difficulties compounded by the tissue inaccessibility.

We tested cotyledon developmental robustness in wildtype cotyledons, and its genetic basis by using JAW-TCP transcription factors as a tool to perturb the proliferation-differentiation balance. Wild-type cotyledons achieve flat, circular laminae through coordinated post-germination growth. Downregulating JAW-TCPs disrupts this program, in which cotyledons become elliptical, exhibit altered proximodistal versus mediolateral growth, and retain surface curvature longer, revealing that TCP-mediated differentiation is critical for shape robustness.

Quantitative live imaging resolved the growth trajectory of cotyledon development to cellular resolution. Contrary to our prevailing understanding, cell division persists throughout early cotyledon opening, demonstrating that post-germination proliferation actively contributes to morphogenesis. Growth tensor analysis revealed that wild-type cotyledons flatten through isotropic expansion coordinated across tissue, while mutants show persistent growth conflicts between the centre and the margin. This spatial growth imbalance, arising from delayed differentiation, generates lasting curvature and anisotropy.

Our findings establish that cotyledon shape robustness depends on precise temporal control of the proliferation-differentiation transition. TCP factors ensure timely cell cycle exit, enabling the switch to coordinated isotropic expansion that produces flat, symmetrical organs. These results reframe cotyledon development as a proliferation-expansion continuum rather than discrete phases, with genetic regulation of differentiation timing governing final geometry.

Whispers from the wall: a new language for plant stem cells

The plant cell wall acts as a hub that integrates biochemical and mechanical signals. How cell wall patterning regulates stem cell activity in the shoot apical meristem (SAM) remains poorly understood. Using systematic immunocytochemical labelling combined with high-resolution imaging in Arabidopsis, we show that highly methylesterified pectins are enriched in mature walls and are essential for stem cell maintenance. In contrast, demethylesterified pectins are specifically deposited at the cell plate, where they guide the orientation of the cell division plane. This bimodal pectin modification pattern is achieved through a novel mRNA compartmentalization mechanism: the pectin methylesterase PME5 is transcribed during mitosis, but its mRNA is retained within the nucleus by the RNA-binding proteins RZ‑1B and RZ‑1C. PME5 mRNA is released only upon nuclear envelope breakdown (NEBD), enabling rapid translation for robust pectin demethylesterification specifically in newly forming cross walls. The spatiotemporal regulation of pectin methylesterification and its influence on cell division patterns and stem cell maintenance highlight the importance of precise wall remodelling in plant morphogenesis.