Using Optical Tweezers Combined with Total Internal Reflection Microscopy to Study Interactions Between the ER and Golgi in Plant Cells

Spatiotemporal dissection of the Golgi apparatus and the ER-Golgi intermediate compartment in budding yeast

Cargo traffic through the Golgi apparatus is mediated by cisternal maturation, but it remains largely unclear how the cis-cisternae, the earliest Golgi sub-compartment, is generated and how the Golgi matures into the trans-Golgi network (TGN). Here, we use high-speed and high-resolution confocal microscopy to analyze the spatiotemporal dynamics of a diverse set of proteins that reside in and around the Golgi in budding yeast. We find many mobile punctate structures that harbor yeast counterparts of mammalian endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC) proteins, which we term 'yeast ERGIC'. It occasionally exhibits approach and contact behavior toward the ER exit sites and gradually matures into the cis-Golgi. Upon treatment with the Golgi-disrupting agent brefeldin A, the ERGIC proteins form larger aggregates corresponding to the Golgi entry core compartment in plants, while cis- and medial-Golgi proteins are absorbed into the ER. We further analyze the dynamics of several late Golgi proteins to better understand the Golgi-TGN transition. Together with our previous studies, we demonstrate a detailed spatiotemporal profile of the entire cisternal maturation process from the ERGIC to the Golgi and further to the TGN.

Applying Optical Tweezers with TIRF Microscopy to Quantify Physical Interactions Between Organelles in the Plant Endomembrane System

Plant organelles are associated with each other through tethering proteins at membrane contact sites (MCS). Methods such as total internal reflection fluorescence (TIRF) optical tweezers allow us to probe organelle interactions in live plant cells. Optical tweezers (focused infrared laser beams) can trap organelles that have a different refractive index to their surrounding medium (cytosol), whilst TIRF allows us to simultaneously image behaviors of organelles in the thin region of cortical cytoplasm. However, few MCS tethering proteins have so far been identified and tested in a quantitative manner. Automated routines (such as setting trapping laser power and controlling the stage speed and distance) mean we can quantify organelle interactions in a repeatable and reproducible manner. Here we outline a series of protocols which describe laser calibrations required to collect robust data sets, generation of fluorescent plant material (Nicotiana tabacum, tobacco), how to set up an automated organelle trapping routine, and how to quantify organelle interactions (particularly organelle interactions with the endoplasmic reticulum). TIRF-optical tweezers enable quantitative testing of putative tethering proteins to reveal their role in plant organelle associations at MCS. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Microscope system set-up and stability Basic Protocol 2: Generation of transiently expressed fluorescent tobacco tissue by Agrobacterium-mediated infiltration Basic Protocol 3: Setting up an automated organelle trapping routine Basic Protocol 4: Quantifying organelle interactions.

Investigation of Soft Matter Nanomechanics by Atomic Force Microscopy and Optical Tweezers: A Comprehensive Review

Soft matter exhibits a multitude of intrinsic physico-chemical attributes. Their mechanical properties are crucial characteristics to define their performance. In this context, the rigidity of these systems under exerted load forces is covered by the field of biomechanics. Moreover, cellular transduction processes which are involved in health and disease conditions are significantly affected by exogenous biomechanical actions. In this framework, atomic force microscopy (AFM) and optical tweezers (OT) can play an important role to determine the biomechanical parameters of the investigated systems at the single-molecule level. This review aims to fully comprehend the interplay between mechanical forces and soft matter systems. In particular, we outline the capabilities of AFM and OT compared to other classical bulk techniques to determine nanomechanical parameters such as Young's modulus. We also provide some recent examples of nanomechanical measurements performed using AFM and OT in hydrogels, biopolymers and cellular systems, among others. We expect the present manuscript will aid potential readers and stakeholders to fully understand the potential applications of AFM and OT to soft matter systems.

Hitchhiking Across Kingdoms: Cotransport of Cargos in Fungal, Animal, and Plant Cells

Eukaryotic cells across the tree of life organize their subcellular components via intracellular transport mechanisms. In canonical transport, myosin, kinesin, and dynein motor proteins interact with cargos via adaptor proteins and move along filamentous actin or microtubule tracks. In contrast to this canonical mode, hitchhiking is a newly discovered mode of intracellular transport in which a cargo attaches itself to an already-motile cargo rather than directly associating with a motor protein itself. Many cargos including messenger RNAs, protein complexes, and organelles hitchhike on membrane-bound cargos. Hitchhiking-like behaviors have been shown to impact cellular processes including local protein translation, long-distance signaling, and organelle network reorganization. Here, we review instances of cargo hitchhiking in fungal, animal, and plant cells and discuss the potential cellular and evolutionary importance of hitchhiking in these different contexts.

Chloroplasts alter their morphology and accumulate at the pathogen interface during infection by Phytophthora infestans

Upon immune activation, chloroplasts switch off photosynthesis, produce antimicrobial compounds and associate with the nucleus through tubular extensions called stromules. Although it is well established that chloroplasts alter their position in response to light, little is known about the dynamics of chloroplast movement in response to pathogen attack. Here, we report that during infection with the Irish potato famine pathogen Phytophthora infestans, chloroplasts accumulate at the pathogen interface, associating with the specialized membrane that engulfs the pathogen haustorium. The chemical inhibition of actin polymerization reduces the accumulation of chloroplasts at pathogen haustoria, suggesting that this process is partially dependent on the actin cytoskeleton. However, chloroplast accumulation at haustoria does not necessarily rely on movement of the nucleus to this interface and is not affected by light conditions. Stromules are typically induced during infection, embracing haustoria and facilitating chloroplast interactions, to form dynamic organelle clusters. We found that infection-triggered stromule formation relies on BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1 (BAK1)-mediated surface immune signaling, whereas chloroplast repositioning towards haustoria does not. Consistent with the defense-related induction of stromules, effector-mediated suppression of BAK1-mediated immune signaling reduced stromule formation during infection. On the other hand, immune recognition of the same effector stimulated stromules, presumably via a different pathway. These findings implicate chloroplasts in a polarized response upon pathogen attack and point to more complex functions of these organelles in plant-pathogen interactions.

Lessons from optical tweezers: quantifying organelle interactions, dynamics and modelling subcellular events

Optical tweezers enable users to physically trap organelles and move them laterally within the plant cell. Recent advances have highlighted physical interactions between functionally related organelle pairs, such as ER-Golgi and peroxisome-chloroplast, and have shown how organelle positioning affects plant growth. Quantification of these processes has provided insight into the force components which ultimately drive organelle movement and positioning in plant cells. Application of optical tweezers has therefore revolutionised our understanding of plant organelle dynamics.

Biomechanical Characterization at the Cell Scale: Present and Prospects

The rapidly growing field of mechanobiology demands for robust and reproducible characterization of cell mechanical properties. Recent achievements in understanding the mechanical regulation of cell fate largely rely on technological platforms capable of probing the mechanical response of living cells and their physico–chemical interaction with the microenvironment. Besides the established family of atomic force microscopy (AFM) based methods, other approaches include optical, magnetic, and acoustic tweezers, as well as sensing substrates that take advantage of biomaterials chemistry and microfabrication techniques. In this review, we introduce the available methods with an emphasis on the most recent advances, and we discuss the challenges associated with their implementation.

Plant organelle dynamics: cytoskeletal control and membrane contact sites

Contents Summary 381 I. Introduction 381 II. Basic movement characteristics 382 III. Actin and associated motors, myosins, play a primary role in plant organelle movement and positioning 382 IV. Mechanisms of myosin recruitment: a tightly regulated system? 384 V. Microtubules, associated motors and interplay with actin 386 VI. Role of organelle interactions: tales of tethers 387 VII. Summary model to describe organelle movement in higher plants 390 VIII. Why is organelle movement important? 390 IX. Conclusions and future perspectives 391 Acknowledgements 391 References 391 SUMMARY: Organelle movement and positioning are correlated with plant growth and development. Movement characteristics are seemingly erratic yet respond to external stimuli including pathogens and light. Given these clear correlations, we still do not understand the specific roles that movement plays in these processes. There are few exceptions including organelle inheritance during cell division and photorelocation of chloroplasts to prevent photodamage. The molecular and biophysical components that drive movement can be broken down into cytoskeletal components, motor proteins and tethers, which allow organelles to physically interact with one another. Our understanding of these components and concepts has exploded over the past decade, with recent technological advances allowing an even more in-depth profiling. Here, we provide an overview of the cytoskeletal and tethering components and discuss the mechanisms behind organelle movement in higher plants.