Visualizing the Integrity of Chloroplast Envelope by Rhodamine and Nile Red Staining

LTD coordinates chlorophyll biosynthesis and LIGHT-HARVESTING CHLOROPHYLL A/B-BINDING PROTEIN transport

Chlorophyll biosynthesis must be tightly coupled to light-harvesting chlorophyll a/b-binding protein (LHCP) biogenesis, as free chlorophyll and its precursors are phototoxic. However, precisely how these 2 processes are coordinated in Arabidopsis (Arabidopsis thaliana) remains elusive. Our previous studies demonstrated the role of LHCP TRANSLOCATION DEFECT (LTD) in delivering LHCPs to the chloroplast via the signal recognition particle-dependent pathway. Here, we show that LTD interacts with and stabilizes the chlorophyll biosynthesis enzymes Mg-protoporphyrin methyltransferase and Mg-protoporphyrin monomethylester (MgPME) cyclase, maintaining their activity. We also demonstrate the direct binding of LTD to MgPME, and through crystal structure analysis, we show that the groove of the LTD dimer is critical for MgPME binding. Thus, we propose that LTD transfers MgPME from Mg-protoporphyrin methyltransferase to the MgPME cyclase. These results elucidate a role for LTD in synchronizing chlorophyll biosynthesis with LHCP transport to ensure the correct insertion of chlorophylls into LHCPs.

Moderate levels of dissolved iron stimulate cellular growth and increase lipid storage in Symbiodinium sp

Dinoflagellates in the family Symbiodiniaceae are fundamental in coral reef ecosystems and facilitate essential processes such as photosynthesis, nutrient cycling, and calcium carbonate production. Iron (Fe) is an essential element for the physiological processes of Symbiodiniaceae, yet its role remains poorly understood in the context of cellular development and metabolic health. Here, we investigated the effect of iron availability-0-100 nM Fe(III)-on Symbiodinium sp. ITS2 type A1 cultures and quantified cellular content using flow cytometry and holotomography. Moderate levels of dissolved Fe (50 nM) enhanced growth rates and cellular content development in Symbiodinium sp., including lipids and proteins. We observed distinct growth patterns, pigment concentrations, and cellular morphology under increasing Fe concentrations, indicating the influence of iron availability on cellular physiology. Nondestructive, label-free holotomographic microscopy enabled single-cell in vivo imaging, revealing higher intracellular lipid accumulation (+57%) in response to 50 nM Fe(III) enrichment. Our findings contribute to a deeper understanding of the relationship between iron availability and Symbiodinium sp. growth and cellular development, with potential implications for coral health and reef resilience in the face of environmental stressors.

Expansion microscopy reveals thylakoid organisation alterations due to genetic mutations and far-red light acclimation

The thylakoid membrane is the site of the light-dependent reactions of photosynthesis. It is a continuous membrane, folded into grana stacks and the interconnecting stroma lamellae. The CURVATURE THYLAKOID1 (CURT1) protein family is involved in the folding of the membrane into the grana stacks. The thylakoid membrane remodels its architecture in response to light conditions, but its 3D organisation and dynamics remain incompletely understood. To resolve these details, an imaging technique is needed that provides high-resolution 3D images in a high-throughput manner. Recently, we have used expansion microscopy, a technique that meets these criteria, to visualise the thylakoid membrane isolated from spinach. Here, we show that this protocol can also be used to visualise enveloped spinach chloroplasts. Additionally, we present an improved protocol for resolving the thylakoid structure of Arabidopsis thaliana. Using this protocol, we show the changes in thylakoid architecture in response to long-term far-red light acclimation and due to knocking out CURT1A. We show that far-red light acclimation results in higher grana stacks that are packed closer together. In addition, the distance between stroma lamellae, which are wrapped around the grana, decreases. In the curt1a mutant, grana have an increased diameter and height, and the distance between grana is increased. Interestingly, in this mutant, the stroma lamellae occasionally approach the grana stacks from the top. These observations show the potential of expansion microscopy to study the thylakoid membrane architecture.

Geminivirus C4/AC4 proteins hijack cellular COAT PROTEIN COMPLEX I for chloroplast targeting and viral infections

Geminiviruses infect numerous crops and cause extensive agricultural losses worldwide. During viral infection, geminiviral C4/AC4 proteins relocate from the plasma membrane to chloroplasts, where they inhibit the production of host defense signaling molecules. However, mechanisms whereby C4/AC4 proteins are transported to chloroplasts are unknown. We report here that tomato (Solanum lycopersicum) COAT PROTEIN COMPLEX I (COPI) components play a critical role in redistributing Tomato yellow leaf curl virus C4 protein to chloroplasts via an interaction between the C4 and β subunit of COPI. Coexpression of both proteins promotes the enrichment of C4 in chloroplasts that is blocked by a COPI inhibitor. Overexpressing or downregulating gene expression of COPI components promotes or inhibits the viral infection, respectively, suggesting a proviral role of COPI components. COPI components play similar roles in C4/AC4 transport and infections of two other geminiviruses: Beet curly top virus and East African cassava mosaic virus. Our results reveal an unconventional role of COPI components in protein trafficking to chloroplasts during geminivirus infection and suggest a broad-spectrum antiviral strategy in controlling geminivirus infections in plants.

Oxygenating respiratoid biosystem for therapeutic cell transplantation

In this study, we address the persistent challenge of providing adequate oxygen to transplanted cells by introducing a respiratoid biosystem. Central to our strategy is the chloroplast-transit-peptide (CTP), crucial for optimal oxygenation. Through conjugation of CTP with alginate, we achieve stabilization of chloroplast structure. Strategically anchored to the outer chloroplast membrane, CTP not only ensures structural integrity but also upregulates key photosynthesis-associated genes. This biosystem demonstrates exceptional efficacy in spontaneously generating oxygen, particularly under hypoxic conditions (~1% pO2). In an application, pancreatic islets encapsulated within the respiratoid biosystem and intraperitoneally implanted in diabetic mice maintain normal glucose levels effectively. Insulin secretion persists for 100 days post-xenotransplantation without the need for immunosuppressant administration, highlighting the reliance on the respiratoid biosystem's oxygen supply and structural stability. Our study demonstrates the respiratoid biosystem as a platform in tissue engineering, offering a nature-inspired solution to the critical challenge of spontaneous oxygen supply.

A novel in-situ-process technique constructs whole circular cpDNA library

BACKGROUND

The chloroplast genome (cp genome) is directly related to the study and analysis of molecular phylogeny and evolution of plants in the phylogenomics era. The cp genome, whereas, is highly plastic and exists as a heterogeneous mixture of sizes and physical conformations. It is advantageous to purify/enrich the circular chloroplast DNA (cpDNA) to reduce sequence complexity in cp genome research. Large-insert, ordered DNA libraries are more practical for genomics research than conventional, unordered ones. From this, a technique of constructing the ordered BAC library with the goal-insert cpDNA fragment is developed in this paper.

RESULTS

This novel in-situ-process technique will efficiently extract circular cpDNA from crops and construct a high-quality cpDNA library. The protocol combines the in-situ chloroplast lysis for the high-purity circular cpDNA with the in-situ substitute/ligation for the high-quality cpDNA library. Individually, a series of original buffers/solutions and optimized procedures for chloroplast lysis in-situ is different than bacterial lysis in-situ; the in-situ substitute/ligation that reacts on the MCE membrane is suitable for constructing the goal-insert, ordered cpDNA library while preventing the large-insert cpDNA fragment breakage. The goal-insert, ordered cpDNA library is arrayed on the microtiter plate by three colonies with the definite cpDNA fragment that are homologous-corresponds to the whole circular cpDNA of the chloroplast.

CONCLUSION

The novel in-situ-process technique amply furtherance of research in genome-wide functional analysis and characterization of chloroplasts, such as genome sequencing, bioinformatics analysis, cloning, physical mapping, molecular phylogeny and evolution.

Chloroplast Isolation in Agavaceas

Chloroplast isolation protocols have been extensively developed for various species of plants, particularly model organisms with easily manipulable physical characteristics. However, succulent plants, such as Agave angustifolia Haw., which possess adaptations for arid environments like the Crassulacean acid metabolism (CAM) and a thicker cuticle, have received less attention, resulting in a potential knowledge gap. This chapter presents a specialized protocol focusing on isolating chloroplast from A. angustifolia, a species exhibiting adaptations to arid conditions and holding ecological and economic significance due to its role in producing bacanora and mezcal beverages. By successfully isolating chloroplast from A. angustifolia plant growth in ex vitro and in vitro conditions, this protocol enables comprehensive future analyses to elucidate metabolic processes and explore potential applications in related species. Consequently, this research aims to bridge this knowledge gap in chloroplast isolation for succulent plants, providing new insights for future investigations in the field.

Live-cell imaging of the chloroplast outer envelope membrane using fluorescent dyes

Chloroplasts are organelles composed of sub-organellar compartments-stroma, thylakoids, and starch granules-and are surrounded by outer and inner envelope membranes (OEM and IEM, respectively). The chloroplast OEM and IEM play key roles not only as a barrier separating the chloroplast components from the cytosol but also in the interchange of numerous metabolites and proteins between the chloroplast interior and the cytosol. Fluorescent protein markers for the chloroplast OEM have been widely used to visualize the outermost border of chloroplasts. However, the use of marker proteins requires an established cellular genetic transformation method, which limits the plant species in which marker proteins can be used. Moreover, the high accumulation of OEM marker proteins often elicits abnormal morphological phenotypes of the OEM. Because the OEM can currently only be visualized using exogenous marker proteins, the behaviors of the chloroplast and/or its OEM remain unknown in wild-type cells of various plant species. Here, we visualized the OEM using live-cell staining with the fluorescent dyes rhodamine B and Nile red in several plant species, including crops. We propose rhodamine B and Nile red as new tools for visualizing the chloroplast OEM in living plant cells that do not require genetic transformation.

Significance Statement

We established a live-cell imaging method to visualize the chloroplast outer envelope membrane by staining living cells with fluorescent dyes. This method does not require genetic transformation and allows the observation of the chloroplast outer envelope membrane in various plant species.

Assessment of WO3 electrode modified with intact chloroplasts as a novel biohybrid platform for photocurrent improvement

The present work describes an easy way to prepare a Chloroplast/PDA@WO₃ biohybrid platform based on the deposition of chloroplasts on WO₃ substrate previously modified with polydopamine (PDA) film as anchoring agent. The use of PDA as an immobilization matrix for chloroplasts, and also as an electron mediator under LED irradiation, resulted in enhanced photocurrents. The use of the chloroplasts amplified the photocurrent, when compared to the bare substrate (WO₃). The best electrode performance was obtained using high intensity LED irradiation at 395 nm, for the electrode exposed for 10 min to 150 μg mL^-1 of intact chloroplasts. Amperometric curves obtained by on/off cycles using an applied potential of +0.50 V, in PBS electrolyte (pH 7.0), showed that the presence of 0.2 × 10^-3 mol L^-1 of simazine caused an approximately 50% decrease of the photobiocurrent. Preliminary studies indicated that the synthesized platform based on intact chloroplasts is a good strategy for studying the behavior of photosynthetic entities, using an LED light-responsive WO₃ semiconductor substrate. This work contributes to the understanding of photobiocatalysts that emerge as a new class of materials with sophisticated and intricate structures. These are promising materials with remarkably improved quantum efficiency with potential applications in photobioelectrocatalysis.