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1. Imaging-based screen identifies novel natural compounds that perturb cell and chloroplast division in Chlamydomonas reinhardtii

   https://doi.org/10.1091/mbc.E24-09-0425  

   Clark-Cotton, Manuella R; Chen, Sheng-An; Gomez, Aracely; Mulabagal, Aditya J; Perry, Adriana; Malhotra, Varenyam; Onishi, Masayuki (April 2025, Molecular Biology of the Cell)

   Schroeder, Courtney (Ed.)

   Successful cell division requires faithful division and segregation of organelles into daughter cells. The unicellular alga Chlamydomonas reinhardtii has a single, large chloroplast whose division is spatiotemporally coordinated with furrowing. Cytoskeletal structures form in the same plane at the midzone of the dividing chloroplast (FtsZ) and the cell (microtubules), but how these structures are coordinated is not understood. Previous work showed that loss of F-actin blocks chloroplast division but not furrow ingression, suggesting that pharmacological perturbations can disorganize these events. In this study, we developed an imaging platform to screen natural compounds that perturb cell division while monitoring FtsZ and microtubules and identified 70 unique compounds. One compound, curcumin, has been proposed to bind to both FtsZ and tubulin proteins in bacteria and eukaryotes, respectively. In C. reinhardtii, where both targets coexist and are involved in cell division, curcumin at a specific dose range caused a severe disruption of the FtsZ ring in chloroplast while leaving the furrow-associated microtubule structures largely intact. Time-lapse imaging showed that loss of FtsZ and chloroplast division failure delayed the completion of furrowing but not the initiation, suggesting that the chloroplast division checkpoint proposed in other algae requires FtsZ or is absent altogether in C. reinhardtii. 

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2. Cleavage-furrow formation without F-actin in Chlamydomonas

   https://doi.org/10.1073/pnas.1920337117  

   Onishi, Masayuki; Umen, James_G; Cross, Frederick_R; Pringle, John_R (July 2020, Proceedings of the National Academy of Sciences)

   Significance Studies of eukaryotic cell division have focused on the actomyosin ring, whose filaments of F-actin and myosin-II are hypothesized to generate the contractile force for ingression of the cleavage furrow. However, myosin-II has a very limited taxonomic distribution, whereas division by furrowing is much more widespread. We used the green algaChlamydomonas reinhardtiito investigate how a furrow can form without myosin-II and the potential roles of F-actin in this process. Although F-actin was associated with ingressing furrows, its complete removal only modestly delayed furrowing, suggesting that an actin-independent mechanism (possibly involving microtubules) drives furrow ingression. Such a mechanism presumably emerged early in eukaryotic evolution and may still underlie cell division in a diverse range of modern species. 

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3. Callose deposition is essential for the completion of cytokinesis in the unicellular alga, Penium margaritaceum

   https://doi.org/10.1242/jcs.249599  

   Davis, Destiny J.; Wang, Minmin; Sørensen, Iben; Rose, Jocelyn K.; Domozych, David S.; Drakakaki, Georgia (December 2020, Journal of Cell Science)

   null (Ed.)

   Cytokinesis in land plants involves the formation of a cell plate that develops into the new cell wall. Callose, a β-1,3 glucan accumulates at later stages of cell plate development presumably to stabilize this delicate membrane network during expansion. Cytokinetic callose is considered specific to multicellular plant species, as it has not been detected in unicellular algae. Here we present callose at the cytokinesis junction of the unicellular charophyte, P. margaritaceum. Callose deposition at the division plane of P. margaritaceum showed distinct, spatiotemporal patterns likely representing distinct roles of this polymer in cytokinesis. Pharmacological inhibition by Endosidin 7 resulted in cytokinesis defects, consistent with the essential role for this polymer in P. margaritaceum cell division. Cell wall deposition at the isthmus zone was also affected by the absence of callose, demonstrating the dynamic nature of new wall assembly in P. margaritaceum. The identification of candidate callose synthase genes provides molecular evidence for callose biosynthesis in P. margaritaceum. The evolutionary implications of cytokinetic callose in this unicellular Zygnematopycean alga is discussed in the context of the conquest of land by plants. 

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4. Volvox and volvocine green algae

   https://doi.org/doi: 10.1186/s13227-020-00158-7  

   Umen, James G (July 2020, EvoDevo)

   The transition of life from single cells to more complex multicellular forms has occurred at least two dozen times among eukaryotes and is one of the major evolutionary transitions, but the early steps that enabled multicellular life to evolve and thrive remain poorly understood. Volvocine green algae are a taxonomic group that is uniquely suited to investigating the step-wise acquisition of multicellular organization. The multicellular volvocine species Volvox carteri exhibits many hallmarks of complex multicellularity including complete germ-soma division of labor, asymmetric cell divisions, coordinated tissue-level morphogenesis, and dimorphic sexes-none of which have obvious analogs in its closest unicellular relative, the model alga Chlamydomonas reinhardtii. Here, I summarize some of the key questions and areas of study that are being addressed with Volvox carteri and how increasing genomic information and methodologies for volvocine algae are opening up the entire group as an integrated experimental system for exploring the evolution of multicellularity and more. 

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5. Multiomics resolution of molecular events during a day in the life of Chlamydomonas

   https://doi.org/10.1073/pnas.1815238116  

   Strenkert, Daniela; Schmollinger, Stefan; Gallaher, Sean D.; Salomé, Patrice A.; Purvine, Samuel O.; Nicora, Carrie D.; Mettler-Altmann, Tabea; Soubeyrand, Eric; Weber, Andreas P. M.; Lipton, Mary S.; et al (February 2019, Proceedings of the National Academy of Sciences)

   The unicellular green algaChlamydomonas reinhardtiidisplays metabolic flexibility in response to a changing environment. We analyzed expression patterns of its three genomes in cells grown under light–dark cycles. Nearly 85% of transcribed genes show differential expression, with different sets of transcripts being up-regulated over the course of the day to coordinate cellular growth before undergoing cell division. Parallel measurements of select metabolites and pigments, physiological parameters, and a subset of proteins allow us to infer metabolic events and to evaluate the impact of the transcriptome on the proteome. Among the findings are the observations thatChlamydomonasexhibits lower respiratory activity at night compared with the day; multiple fermentation pathways, some oxygen-sensitive, are expressed at night in aerated cultures; we propose that the ferredoxin, FDX9, is potentially the electron donor to hydrogenases. The light stress-responsive genesPSBS,LHCSR1, andLHCSR3show an acute response to lights-on at dawn under abrupt dark-to-light transitions, whileLHCSR3genes also exhibit a later, second burst in expression in the middle of the day dependent on light intensity. Each response to light (acute and sustained) can be selectively activated under specific conditions. Our expression dataset, complemented with coexpression networks and metabolite profiling, should constitute an excellent resource for the algal and plant communities. 

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