Biology subjects

Majda, M.

Publications and source records attributed to Majda, M..

7 recordsLinked to original sources

bioRxiv2026

Maintenance of the leaf cell proliferation boundary by a cell size at division threshold mechanism.

The sizes and shapes of organs are established by the combined actions of cell proliferation and cell growth. In plants, development of the determinate planar leaf is initiated by primordia formation and establishment of abaxial/adaxial polarity [1,2,3]. Lamina outgrowth is driven by cell division and growth along proximo-distal (PD) and medio-lateral (ML) axes [4], established by mutually repressive PD gradients of miRNA and target transcription factors [5,6,7,8]. These gradients generate proximal regions of competence for cell division and increased growth, with distal regions of reduced growth, endoreduplication and differentiation. The transition from proliferation to growth and differentiation is marked by a cell cycle arrest front, which moves basipetally during leaf growth, progressively restricting proximal proliferative zones as the leaf grows [9,10,11]. Intersection of proximal proliferation-promoting gradients with distal differentiation-promoting gradients may delineate the arrest front, but its dynamics remain poorly understood. We reasoned that mutants affecting cell proliferation patterns may provide insights into the formation, maintenance and dissolution of the arrest front. Spatio-temporal modelling of live imaging data of loss of function mutants of the regulatory peptidase DA1 and its E3 ligase activator Big Brother (BB), which increase cell proliferation [12,13], showed that these proteins effectively establish a threshold cell size at division as a function of distance from the base of the growing leaf and the duration of growth. Loss of BB and DA1 activities increased the persistence of cell divisions and dissolved the arrest front. This suggested that the arrest front emerges from the interactions of threshold areas of cell division with the cessation of division over time, and not from an independently-specified boundary.

plant biology↗

bioRxiv2024

SHOOTMERISTEMLESS autoactivation: A prerequisite for fruit metamorphosis

In animals and plants, organ shape is primarily determined during primordium development by carefully coordinated growth and cell division1-3. Rare examples of post-primordial change in morphology (reshaping) exist that offer tractable systems to study mechanisms required for organ-shape determination and diversification. One such example is the heart-shape formation of Capsella fruits that occurs by reshaping the ovate spheroid gynoecium upon fertilization4. Here we use whole-organ live-imaging to show that dynamic changes in growth and cell division coupled with local maintenance of meristematic identity drives Capsella fruit-shape formation. At the molecular level, we reveal an auxin-induced mechanism ultimately descending on a single cis regulatory element to mediate morphological alteration. This element resides in the promoter of the Capsella rubella SHOOTMERISTEMLESS5 (CrSTM) gene. The CrSTM meristem identity factor positively regulates its own expression through binding to this element thereby providing a feed-forward loop at the position and time when protrusions emerge to form the heart. Independent evolution of the STM-binding element in STM promoters across Brassicaceae species correlates with those undergoing a gynoecium-to-fruit metamorphosis. Accordingly, genetic and phenotypic studies showed that the STM-binding element is required to facilitate the shape transition and reveals a conserved molecular mechanism for organ morphogenesis.

plant biology↗

bioRxiv2023

Puzzle cell shape emerges from the interaction of growth with mechanical constraints

Puzzle-shaped epidermal cells not only reduce mechanical stress during organ growth but also record the expansion history of the tissue in their outlines. By combining mechanical simulations with time-lapse imaging, we show that transitions from directional to isotropic expansion induce new lobes to form along the previous growth axis, and that switching the order of anisotropic and isotropic phases yields hybrid shapes that reliably preserve those transitions. In maize, model predictions and live imaging coincide precisely, and in Ara-bidopsis, final lobe patterns correlate more with growth history than with cell size alone. Ge-netic or pharmacological disruption of lobe formation constrains leaf expansion or drives compensatory elongation, which underscores a mechanical function. A broad survey of living and fossil vascular plants reveals that the mechanism to make puzzle-shaped cells is both widespread and developmentally plastic, suggesting that single snapshots of leaves can give insight into their growth history. Together, these findings demonstrate that puzzle cells trans-form cell geometry into a living record of how tissues grow.

plant biology↗

bioRxiv2022

Spatial consistency of cell growth direction during organ morphogenesis requires CELLULOSE-SYNTHASE INTERACTIVE1

Extracellular matrices generally contain fibril-like polymers that may be organized in parallel arrays. Although their role in morphogenesis has been long recognized, it is still unclear how the subcellular control of fibril synthesis translates into well-defined organ shape. Here, we addressed this question using the Arabidopsis sepal as a model organ. In plants, cell growth is driven by turgor pressure and restrained by the extracellular matrix known as the cell wall. Cellulose is the main load-bearing component of the plant cell wall and cellulose microfibrils are thought to channel growth perpendicularly to their main orientation. Given the key function of CELLULOSE SYNTHASE INTERACTIVE 1 (CSI1) in guidance of cellulose synthesis, we investigated the role of CSI1 in sepal morphogenesis. We observed that sepals from csi1 mutants are shorter, although their newest cellulose microfibrils are more aligned compared to wild type. Surprisingly, cell growth anisotropy was similar in csi1 and wild-type plants. We resolved this apparent paradox using polarized Raman microspectroscopy, live imaging of growing sepals, and bespoke mechanical assays. We found that CSI1 is required for spatial consistency of growth direction across the sepal and for the maintenance of overall organ elongation. Our work illustrates how the subcellular regulation of the extracellular matrix may control morphogenesis at multiple scales.

developmental biology↗

bioRxiv2021

MorphoGraphX 2.0: Providing context for biological image analysis with positional information

Positional information is a central concept in developmental biology. In developing organs, positional information can be idealized as a local coordinate system that arises from morphogen gradients controlled by organizers at key locations. This offers a plausible mechanism for the integration of the molecular networks operating in individual cells into the spatially-coordinated multicellular responses necessary for the organization of emergent forms. Understanding how positional cues guide morphogenesis requires the quantification of gene expression and growth dynamics in the context of their underlying coordinate systems. Here we present recent advances in the MorphoGraphX software (Barbier de Reuille et al. eLife 2015;4:e05864) that implement a generalized framework to annotate developing organs with local coordinate systems. These coordinate systems introduce an organ-centric spatial context to microscopy data, allowing gene expression and growth to be quantified and compared in the context of the positional information thought to control them.

developmental biology↗

bioRxiv2019

Arabidopsis XTH4 and XTH9 contribute to wood cell expansion and secondary wall formation

In dicotyledons, xyloglucan is the major hemicellulose of primary walls affecting the load-bearing framework with participation of XTH enzymes. We used loss- and gain-of function approaches to study functions of abundant cambial region expressed XTH4 and XTH9 in secondary growth. In secondarily thickened hypocotyls, these enzymes had positive effects on vessel element expansion and fiber intrusive growth. In addition, they stimulated secondary wall thickening, but reduced secondary xylem production. Cell wall analyses of inflorescence stems revealed changes in lignin, cellulose, and matrix sugar composition, indicating overall increase in secondary versus primary walls in the mutants, indicative of higher xylem production compared to wild type (since secondary walls were thinner). Intriguingly, the number of secondary cell wall layers was increased in xth9 and reduced in xth4, whereas the double mutant xth4x9 displayed intermediate number of layers. These changes correlated with certain Raman signals from the walls, indicating changes in lignin and cellulose. Secondary walls were affected also in the interfascicular fibers where neither XTH4 nor XTH9 were expressed, indicating that these effects were indirect. Transcripts involved in secondary wall biosynthesis and in cell wall integrity sensing, including THE1 and WAK2, were highly induced in the mutants, indicating that deficiency in XTH4 and XTH9 triggers cell wall integrity signaling, which, we propose, stimulates the xylem cell production and modulates secondary wall thickening. Prominent effects of XTH4 and XTH9 on secondary xylem support the hypothesis that altered xyloglucan can affect wood properties both directly and via cell wall integrity sensing. SIGNIFICANCE STATEMENTXyloglucan is a ubiquitous component of primary cell walls in all land plants but has not been so far reported in secondary walls. It is metabolized in muro by cell wall-residing enzymes - xyloglucan endotransglycosylases/hydrolases (XTHs), which are reportedly abundant in vascular tissues, but their role in these tissues is unclear. Here we report that two vascular expressed enzymes in Arabidopsis, XTH4 and XTH9 contribute to the secondary xylem cell radial expansion and intrusive elongation in secondary vascular tissues. Unexpectedly, deficiency in their activities highly affect chemistry and ultrastructure of secondary cell walls by non-cell autonomous mechanisms, including transcriptional induction of secondary wall-related biosynthetic genes and cell wall integrity sensors. These results link xyloglucan metabolism with cell wall integrity pathways, shedding new light on previous reports about prominent effects of xyloglucan metabolism on secondary walls. One sentence summaryXTH4 and XTH9 positively regulate xylem cell expansion and fiber intrusive tip growth, and their deficiency alters secondary wall formation via cell wall integrity sensing mechanisms.

developmental biology↗

bioRxiv2018

Anthranilic acid regulates subcellular localization of auxin transporters during root gravitropism

O_LIDistribution of auxin within plant tissues is of great importance for developmental plasticity, including root gravitropic growth. Auxin flow is directed by the subcellular polar distribution and dynamic relocalization of auxin transporters such as the PIN-FORMED (PIN) efflux carriers, which can be influenced by the main natural plant auxin indole-3-acetic acid (IAA). Anthranilic acid (AA) is an important early precursor of IAA and previously published studies with AA analogues suggested that AA may also regulate PIN localization.\nC_LIO_LIUsing Arabidopsis thaliana as a model species, we studied an AA-deficient mutant displaying agravitropic root growth, treated seedlings with AA and AA analogues and transformed lines to over-produce AA while inhibiting its conversion to downstream IAA precursors.\nC_LIO_LIWe showed that AA rescues root gravitropic growth in the AA-deficient mutant at concentrations that do not rescue IAA levels. Overproduction of AA affects root gravitropism without affecting IAA levels. Treatments with, or deficiency in, AA result in defects in PIN polarity and gravistimulus-induced PIN relocalization in root cells.\nC_LIO_LIOur results reveal a previously unknown role for AA in the regulation of PIN subcellular localization and dynamics involved in root gravitropism, which is independent of its better-known role in IAA biosynthesis.\nC_LI

plant biology↗