AbstractDiverging from conventional cell division models, plant cells undergo incomplete division to generate plasmodesmata communication bridges between daughter cells. While fundamental for plant multicellularity, the mechanisms governing bridge stabilization, as opposed to severing, remain unknown. We found that the endoplasmic reticulum (ER) is decisive in promoting incomplete cytokinesis by inhibiting local abscission events. ER tubes within contracting cell plate fenestrae create energy barriers preventing full closure. Contraction ceases upon encountering a metastable ER-plasma membrane tubular structure, leading to plasmodesmata formation. This process relies on the ER-tethers multiple C2 domains and transmembrane domain proteins 3, 4, and 6, which act as ER stabilizers, preserving ER position and integrity in nascent bridges. Our findings unveil the mechanisms through which plants undergo incomplete division to promote intercellular communication.One-Sentence SummaryUninterrupted ER connections obstruct abscission, causing incomplete cytokinesis and plasmodesmata formation in plants.

Anionic phospholipids (PS, PA, PI, PIPs) are low-abundant phospholipids with impactful functions in cell signaling, membrane trafficking and cell differentiation processes. They can be quickly metabolized and can transiently accumulate at defined spots within the cell or an organ to respond to physiological or environmental stimuli. As even a small change in their composition profile will produce a significant effect on biological processes, it is crucial to develop a sensitive and optimized analytical method to accurately detect and quantify them. While thin-layer chromatography (TLC) separation coupled with gas chromatography (GC) detection methods already exist, they do not allow for precise, sensitive, and accurate quantification of all anionic phospholipid species. Here we developed a method based on high-performance liquid chromatography (HPLC) combined with two-dimensional mass spectrometry (MS2 ) by MRM mode to detect and quantify all molecular species and classes of anionic phospholipids in one shot. This method is based on a derivatization step by methylation that greatly enhances the ionization, the separation of each peak, the peak resolution as well as the limit of detection and quantification for each individual molecular species, and more particularly for PA and PS. Our method universally works in various plant samples. Remarkably, we identified that PS is enriched with very long chain fatty acids in the roots but not in aerial organs of Arabidopsis thaliana. Our work thus paves the way for new studies on how the composition of anionic lipids is finely tuned during plant development and environmental responses.

Molecular motifs can explain information processing within single cells, while how assemblies of cells collectively achieve this remains less well understood. Plant fitness and survival depend upon robust and accurate decision-making in their decentralised multicellular organ systems. Mobile agents, including hormones, metabolites, and RNAs, have a central role in coordinating multicellular collective decision-making, yet mechanisms describing how cell–cell communication scales to organ-level transitions is poorly understood. Here, we explore how unified outputs may emerge in plant organs by distributed information processing across different scales and using different modalities. Mathematical and computational representations of these events are also explored toward understanding how these events take place and are leveraged to manipulate plant development in response to the environment.

SummaryEndoplasmic Reticulum (ER)-to-Golgi trafficking is a central process of the secretory system of eukaryotic cells that ensures proper spatiotemporal sorting of proteins and lipids1–5. However, the nature of the ER-Golgi Intermediate Compartments (ERGIC) and the molecular mechanisms mediating the transition between the ERGIC and the Golgi, as well as the universality of these processes amongst Eukaryotes, remain undiscovered. Here, we took advantage of the plant cell system in which the Golgi is highly dynamic and in close vicinity to the ER6–9. We discovered that the ERGIC is composed from at least two distinct subpopulations ofcis-Golgi. A subpopulation is a reticulated tubulo-vesicular network mostly independent from the Golgi, highly dynamic at the ER-Golgi interface and crossed by ER-induced release of luminal cargos at early stage. Another subpopulation is more stable, cisterna-like and mostly associated to the Golgi. Our results identified that the generation and dynamics of the ER-Golgi intermediate tubulo-vesicular network is regulated by the acyl-chain length of sphingolipids as well as the contacts it establishes with existing Golgi cisternae. Our study is a major twist in the understanding of the Golgi by identifying that the ERGIC in plants is a Golgi-independent highly dynamic tubular network from which arise more stable cisternae-like Golgi structures. This novel model presents a mechanism for early secretory trafficking adapted to respond to developmental and environmental stimuli, including susceptibility or resistance to diseases, autophagy or cell-reprograming.

Lipids are not only structural elements that make up biological membranes, they also play a crucial role in functionalizing these membranes. Through their ability to modulate membrane physical properties, to act as sensors and signaling molecules, and to interact with proteins to influence their subcellular localization and activity, lipids contribute the intricate workings of plant cells. The enrichment of specific lipids within distinct subcellular compartments aids to the establishment of membranes unique identity and properties. Lipids are major regulators of many cellular processes including cell signaling, cell division, cell polarity, membrane trafficking, intra- and intercellular communication, cell growth, and responses to environmental stress. In fact, the immense diversity of lipid species provides plant cells with an extensive arsenal of tools to establish distinctive biochemical identities within their membranes. In this review, we present an overview of plant membrane lipids, emphasizing their role in environmental stress response by highlighting recent advancements in the field.

AbstractTheFW2.2gene is the founding member of theCELL NUMBER REGULATOR(CNR) gene family. More than 20 years ago,FW2.2was the first cloned gene underlying a Quantitative Trait Locus (QTL) governing fruit size/weight in tomato. However, despite this discovery, the molecular mechanisms by which FW2.2 acts as a negative regulator of cell divisions during fruit growth remain undeciphered. In the present study, we confirm that FW2.2 is a transmembrane spanning protein, whose both N- and C-terminal ends are facing the apoplast. We unexpectedly found that FW2.2 is located at plasmodesmata (PD). FW2.2 participates in the spatiotemporal regulation of callose deposition at PD via an interaction with Callose Synthases, which suggests a regulatory role in cell-to-cell communication by modulating PD transport capacity and trafficking of signaling molecules during fruit development.

Plant viruses represent a risk to agricultural production and as only few treatments exist, it is urgent to identify resistance mechanisms and factors. In plant immunity, plasma membrane (PM)-localized proteins are playing an essential role in sensing the extracellular threat presented by bacteria, fungi or herbivores. Viruses being intracellular pathogens, the role of the plant PM in detection and resistance against viruses is often overlooked. We investigated the role of the partially PM-bound Calcium-dependent protein kinase 3 (CPK3) in viral infection and we discovered that it displayed a specific ability to hamper viral propagation over CPK isoforms that are involved in immune response to extracellular pathogens. More and more evidence support that the lateral organization of PM proteins and lipids underlies signal transduction in plants. We showed here that CPK3 diffusion in the PM is reduced upon activation as well as upon viral infection and that such immobilization depended on its substrate, Remorin (REM1.2), a scaffold protein. Furthermore, we discovered that the viral infection induced a CPK3-dependent increase of REM1.2 PM diffusion. Such interdependence was also observable regarding viral propagation. This study unveils a complex relationship between a kinase and its substrate that contrasts with the commonly described co-stabilisation upon activation while it proposes a PM-based mechanism involved in decreased sensitivity to viral infection in plants.

Plant viruses represent a risk to agricultural production and as only few treatments exist, it is urgent to identify resistance mechanisms and factors. In plant immunity, plasma membrane (PM)-localized proteins are playing an essential role in sensing the extracellular threat presented by bacteria, fungi or herbivores. Viruses being intracellular pathogens, the role of the plant PM in detection and resistance against viruses is often overlooked. We investigated the role of the partially PM-bound Calcium-dependent protein kinase 3 (CPK3) in viral infection and we discovered that it displayed a specific ability to hamper viral propagation over CPK isoforms that are involved in immune response to extracellular pathogens. More and more evidence support that the lateral organization of PM proteins and lipids underlies signal transduction in plants. We showed here that CPK3 diffusion in the PM is reduced upon activation as well as upon viral infection and that such immobilization depended on its substrate, Remorin (REM1.2), a scaffold protein. Furthermore, we discovered that the viral infection induced a CPK3-dependent increase of REM1.2 PM diffusion. Such interdependence was also observable regarding viral propagation. This study unveils a complex relationship between a kinase and its substrate that contrasts with the commonly described co-stabilisation upon activation while it proposes a PM-based mechanism involved in decreased sensitivity to viral infection in plants.

AbstractMultiple C2 Domains and Transmembrane region Proteins (MCTPs) in plants have been identified as important functional and structural components of plasmodesmata cytoplasmic bridges, which are vital for cell-cell communication. MCTPs are endoplasmic reticulum (ER)-associated proteins which contain three to four C2 domains and two transmembrane regions. In this study, we created structural models ofArabidopsisMCTP4 ER-anchor transmembrane region (TMR) domain using several prediction methods based on deep learning. This region, critical for driving ER association, presents a complex domain organization and remains largely unknown. Our study demonstrates that using a single deep-learning method to predict the structure of membrane proteins can be challenging. Our deep learning models presented three different conformations for the MCTP4 structure, provided by different deep learning methods, indicating the potential complexity of the protein’s conformational landscape. For the first time, we used simulations to explore the behaviour of the TMR of MCTPs within the lipid bilayer. We found that the TMR of MCTP4 is not rigid, but can adopt various conformations including some not identified by deep learning tools. These findings underscore the complexity of predicting protein structures. We learned that combining different methods, such as deep learning and simulations, enhances our understanding of complex proteins.

ABSTRACTPlant viruses represent a risk to agricultural production and as only few treatments exist, it is urgent to identify resistance mechanisms and factors. In plant immunity, plasma membrane (PM)-localized proteins are playing an essential role in sensing the extracellular threat presented by bacteria, fungi or herbivores. Viruses being intracellular pathogens, the role of the plant PM in detection and resistance against viruses is often overlooked. We investigated the role of the partially PM-bound Calcium-dependent protein kinase 3 (CPK3) in viral infection and we discovered that it displayed a specific ability to hamper viral propagation over CPK isoforms that are involved in immune response to extracellular pathogens. More and more evidence support that the lateral organization of PM proteins and lipids underlies signal transduction in plants. We showed here that CPK3 diffusion in the PM is reduced upon activation as well as upon viral infection and that such immobilization depended on its substrate, Remorin (REM1.2), a scaffold protein. Furthermore, we discovered that the viral infection induced a CPK3-dependent increase of REM1.2 PM diffusion. Such interdependence was also observable regarding viral propagation. This study unveils a complex relationship between a kinase and its substrate that contrasts with the commonly described co-stabilisation upon activation while it proposes a PM-based mechanism involved in decreased sensitivity to viral infection in plants.