Biology subjects

Bellani, E.

Publications and source records attributed to Bellani, E..

3 recordsLinked to original sources

bioRxiv2026

Mechanical cues trigger phellem differentiation during barrier transition

A continuous and uninterrupted barrier tissue is essential for protecting internal tissues from the external environment. In many dicot roots, the endodermis fulfils this role during primary growth; however, the onset of secondary growth in the vascular tissue coincides with the rupture of the overlying endodermis and formation of a new barrier, the periderm, beneath it. Despite the importance of barrier integrity for plant survival, the mechanisms coordinating this barrier transition have remained unexplored. Here, we show that endodermal rupture in Arabidopsis thaliana roots releases mechanical constraints on the underlying properiderm. This release leads to cell expansion and triggers differentiation of the outermost properiderm cells into phellem, a ligno-suberized barrier cell type. Premature relief of mechanical constraints, through hyperosmotic stress or targeted endodermal ablation, is sufficient to trigger phellem differentiation. FERONIA, a cell wall integrity receptor kinase, is required for phellem differentiation in response to mechanical stress. Overall, our findings establish mechanical stress as an instructive cue for phellem differentiation, revealing how plants convert mechanical signals into robust, adaptive protective barriers.

plant biology↗

bioRxiv2025

Imaging of specialized plant cell walls by improved cryo-CLEM and cryo-electron tomography

Cryo-focused ion beam scanning electron microscopy (cryo-FIBSEM) has become essential for preparing electron-transparent lamellae from cryo-plunged and high-pressure frozen specimens. However, targeting specific cellular features within large, complex organs remains challenging. Here we present a series of technical improvements significantly enhancing the efficiency and accessibility of the Serial Lift-Out and SOLIST (Serialized On-grid Lift-In Sectioning for Tomography) procedures that are revolutionizing the field. We were able to extend the cryo-FIBSEM session from 24 hours to 5 days without interruptions. In addition, we describe a modified silver-plated EasyLiftTM needle that eliminates the need of the copper or gold block between the original tungsten needle and the sample. Moreover, we describe a strategy that significantly reduces curtaining effects. Finally, we report a precise routine to target a lamella with a precision of approximately 1 {micro}m in X,Y and Z. Together, these modifications considerably reduce contamination risk and preparation time, making cryo-lift-out techniques more accessible for routine structural biology applications on any type of tissue. Here, we demonstrate the power of our technique by targeting several specific wall structures that are of crucial importance for root function in plants and that were previously inaccessible to cryo-electron tomography (cryo-ET). High-pressure freezing (HPF) of plant tissues presents unique challenges for cryo-electron microscopy sample preparation due to the overall sample size, the individual cells size, their rigid cell wall and finally, their large vacuoles, which contain large amounts of rather diluted water solutions compared to cytosol. The internal root structures targeted are the Casparian strip (CS), suberin lamellae (SL), as well as secondary wall of xylem vessels, requiring reaching a targeting precision of 5 m in a 3 mm long and 80-120 m thick root tip. Our technological improvements for the cryo-correlative light and electron microscopy (cryo-CLEM) workflow enabled successful, targeted cryo-ET in plant roots. We noticed that, despite ice formation in vacuoles and to some degree in the cytosol, the plasma membranes and cell walls are remarkably well preserved, providing stunning insights into the native, hydrated nano-structure of plant cell walls, previously only observable with contrasting agents and in a dehydrated state.

plant biology↗

bioRxiv2022

Directed growth and fusion of membrane-wall microdomains requires CASP-mediated inhibition and displacement of secretory foci

Casparian strips (CS), the main extracellular diffusion barrier in plant roots, are precisely localized cell wall lignin-impregnations, contrasting animal tight-junctions. The CS membrane domain (CSD) proteins 1-5 (CASP1-5) define and accumulate at the CS associated membrane domains displaying matrix adhesion and protein exclusion. A full CASP knock-out (caspQ) now reveals that CASPs are not needed for localization of lignification or lignin-polymerizing enzymes, since correctly aligned spots still form in the mutant. Ultra-structurally, however, these spots appear as highly disorganized secretory foci, with neither exclusion zone nor membrane attachment and excessive cell wall growth. Biotin proximity labelling identifies RabA-GTPases as potential CASP-interactors. We confirm their localisation and function at the CSD, similar to exocyst subunits, known Rab effectors. Our work reveals that CASPs enforce displacement of initial secretory foci through exclusion of vesicle tethering factors, thereby ensuring rapid fusion of microdomains and effective sealing of the cell wall space.

plant biology↗