Authors: Zeyu Jin, Li Wan, Yuqi Zhang...

The TOC and TIC complexes are essential translocons that facilitate the import of the nuclear genome-encoded preproteins across the two envelope membranes of chloroplast, but their exact molecular identities and assembly remain unclear. Here, we report a cryoelectron microscopy structure of TOC-TIC supercomplex from Chlamydomonas, containing a total of 14 identified components. The preprotein-conducting pore of TOC is a hybrid β-barrel co-assembled by Toc120 and Toc75, while the potential translocation path of TIC is formed by transmembrane helices from Tic20 and YlmG, rather than a classic model of Tic110. A rigid intermembrane space (IMS) scaffold bridges two chloroplast membranes, and a large hydrophilic cleft on the IMS scaffold connects TOC and TIC, forming a pathway for preprotein translocation. Our study provides structural insights into the TOC-TIC supercomplex composition, assembly, and preprotein translocation mechanism, and lays a foundation to interpret the evolutionary conservation and diversity of this fundamental translocon machinery.

Topics: Chloroplasts; Cryoelectron Microscopy; Intracellular Membranes; Protein Transport; Chlamydomonas; Multiprotein Complexes; Algal Proteins

PubMed: 36413996
DOI: 10.1016/j.cell.2022.10.030

Authors: Junhao Huang, Hui Tao, Jikun Chen...

Mastigonemes, the hair-like lateral appendages lining cilia or flagella, participate in mechanosensation and cellular motion, but their constituents and structure have remained unclear. Here, we report the cryo-EM structure of native mastigonemes isolated from Chlamydomonas at 3.0 Å resolution. The long stem assembles as a super spiral, with each helical turn comprising four pairs of anti-parallel mastigoneme-like protein 1 (Mst1). A large array of arabinoglycans, which represents a common class of glycosylation in plants and algae, is resolved surrounding the type II poly-hydroxyproline (Hyp) helix in Mst1. The EM map unveils a mastigoneme axial protein (Mstax) that is rich in heavily glycosylated Hyp and contains a PKD2-like transmembrane domain (TMD). Mstax, with nearly 8,000 residues spanning from the intracellular region to the distal end of the mastigoneme, provides the framework for Mst1 assembly. Our study provides insights into the complexity of protein and glycan interactions in native bio-architectures.

Topics: Chlamydomonas; Cilia; Flagella; Polysaccharides; Proteins

PubMed: 38552612
DOI: 10.1016/j.cell.2024.02.037

Review

Authors: Susan K Dutcher

The generation of ciliary waveforms requires the spatial and temporal regulation of dyneins. This review catalogues many of the asymmetric structures and proteins in the cilia of , a unicellular alga with two cilia that are used for motility in liquid medium. These asymmetries, which have been identified through mutant analysis, cryo-EM tomography and proteomics, provide a wealth of information to use for modelling how waveforms are generated and propagated. This article is part of the Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.

Topics: Chlamydomonas; Cilia; Electron Microscope Tomography; Proteomics

PubMed: 31884924
DOI: 10.1098/rstb.2019.0153

Authors: Marylou C Machingura, James V Moroney

In Chlamydomonas the different stages of the Calvin-Benson cycle take place in separate locations within the chloroplast.

Topics: Chlamydomonas; Chlamydomonas reinhardtii; Chloroplasts; Photosynthesis; Ribulose-Bisphosphate Carboxylase

PubMed: 30426925
DOI: 10.7554/eLife.42507

Review

Authors: Adrien Burlacot, Gilles Peltier, Yonghua Li-Beisson...

Microalgae have emerged as a promising platform for production of carbon- and energy- rich molecules, notably starch and oil. Establishing an economically viable algal biotechnology sector requires a holistic understanding of algal photosynthesis, physiology, cell cycle and metabolism. Starch/oil productivity is a combined effect of their cellular content and cell division activities. Cell growth, starch and fatty acid synthesis all require carbon building blocks and a source of energy in the form of ATP and NADPH, but with a different requirement in ATP/NADPH ratio. Thus, several cellular mechanisms have been developed by microalgae to balance ATP and NADPH supply which are essentially produced by photosynthesis. Major energy management mechanisms include ATP production by the chloroplast-based cyclic electron flow and NADPH removal by water-water cycles. Furthermore, energetic coupling between chloroplast and other cellular compartments, mitochondria and peroxisome, is increasingly recognized as an important process involved in the chloroplast redox poise. Emerging literature suggests that alterations of energy management pathways affect not only cell fitness and survival, but also influence biomass content and composition. These emerging discoveries are important steps towards diverting algal photosynthetic energy to useful products for biotechnological applications.

Topics: Adenosine Triphosphate; Carbon; Chlamydomonas; Electron Transport; NADP; Photosynthesis; Starch

PubMed: 31561610
DOI: 10.3390/cells8101154

Authors: Joel Rosenbaum

Topics: Animals; Biological Transport, Active; Caenorhabditis elegans; Cell Movement; Chlamydomonas; Cilia; Flagella; Movement

PubMed: 11864582
DOI: 10.1016/s0960-9822(02)00703-0

Review

Authors: Frederick R Cross, James G Umen

The position of Chlamydomonas within the eukaryotic phylogeny makes it a unique model in at least two important ways: as a representative of the critically important, early-diverging lineage leading to plants; and as a microbe retaining important features of the last eukaryotic common ancestor (LECA) that has been lost in the highly studied yeast lineages. Its cell biology has been studied for many decades and it has well-developed experimental genetic tools, both classical (Mendelian) and molecular. Unlike land plants, it is a haploid with very few gene duplicates, making it ideal for loss-of-function genetic studies. The Chlamydomonas cell cycle has a striking temporal and functional separation between cell growth and rapid cell division, probably connected to the interplay between diurnal cycles that drive photosynthetic cell growth and the cell division cycle; it also exhibits a highly choreographed interaction between the cell cycle and its centriole-basal body-flagellar cycle. Here, we review the current status of studies of the Chlamydomonas cell cycle. We begin with an overview of cell-cycle control in the well-studied yeast and animal systems, which has yielded a canonical, well-supported model. We discuss briefly what is known about similarities and differences in plant cell-cycle control, compared with this model. We next review the cytology and cell biology of the multiple-fission cell cycle of Chlamydomonas. Lastly, we review recent genetic approaches and insights into Chlamydomonas cell-cycle regulation that have been enabled by a new generation of genomics-based tools.

Topics: Animals; Cell Cycle; Chlamydomonas; Cytokinesis; Gene Expression Regulation; Mutation; Phylogeny; Plants; Viridiplantae

PubMed: 25690512
DOI: 10.1111/tpj.12795

Review

Authors: Michael Schroda, Dorothea Hemme, Timo Mühlhaus...

Heat waves occurring at increased frequency as a consequence of global warming jeopardize crop yield safety. One way to encounter this problem is to genetically engineer crop plants toward increased thermotolerance. To identify entry points for genetic engineering, a thorough understanding of how plant cells perceive heat stress and respond to it is required. Using the unicellular green alga Chlamydomonas reinhardtii as a model system to study the fundamental mechanisms of the plant heat stress response has several advantages. Most prominent among them is the suitability of Chlamydomonas for studying stress responses system-wide and in a time-resolved manner under controlled conditions. Here we review current knowledge on how heat is sensed and signaled to trigger temporally and functionally grouped sub-responses termed response elements to prevent damage and to maintain cellular homeostasis in plant cells.

Topics: Calcium; Cell Cycle Checkpoints; Cell Membrane; Chlamydomonas; Chlamydomonas reinhardtii; Heat-Shock Response; Plant Cells; Plant Proteins; Protein Kinases; Signal Transduction

PubMed: 25754362
DOI: 10.1111/tpj.12816

Authors: Christoph Benning

Topics: Biofuels; Chlamydomonas; Photosynthesis; Research

PubMed: 25906814
DOI: 10.1111/tpj.12831

Review

Authors: Severin Sasso, Herwig Stibor, Maria Mittag...

In the mid-20th century, the unicellular and genetically tractable green alga was first developed as a model organism to elucidate fundamental cellular processes such as photosynthesis, light perception and the structure, function and biogenesis of cilia. Various studies of have profoundly advanced plant and cell biology, and have also impacted algal biotechnology and our understanding of human disease. However, the 'real' life of in the natural environment has largely been neglected. To extend our understanding of the biology of , it will be rewarding to explore its behavior in its natural habitats, learning more about its abundance and life cycle, its genetic and physiological diversity, and its biotic and abiotic interactions.

Topics: Chlamydomonas reinhardtii; Ecosystem; Genomics; Phylogeography

PubMed: 30382941
DOI: 10.7554/eLife.39233