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The green microalga Dunaliella salina hyperaccumulates β‐carotene in the chloroplast, which turns its cells orange. This does not occur in the sister species Dunaliella tertiolecta. However, the molecular mechanisms of β‐carotene hyperaccumulation were still unclear. Here, we discovered the reasons for β‐carotene hyperaccumulation by comparing the morphology, physiology, genome, and transcriptome between the carotenogenic D. salina and the noncarotenogenic D. tertiolecta after transfer to high light. The differences in photosynthetic capacity, cell growth, and the concentration of stored carbon suggest that these species regulate the supply and utilization of carbon differently. The number of β‐carotene‐containing plastid lipid globules increased in both species, but much faster and to a greater extent in D. salina than in D. tertiolecta. Consistent with the accumulation of plastid lipid globules, the expression of the methyl‐erythritol‐phosphate and carotenoid biosynthetic pathways increased only in D. salina, which explains the de novo synthesis of β‐carotene. In D. salina, the concomitantly upregulated expression of the carotene globule proteins suggests that hyperaccumulation of β‐carotene also requires a simultaneous increase in its sink capacity. Based on genomic analysis, we propose that D. salina has genetic advantages for routing carbon from growth to carotenoid metabolism. Summary statement: Under high light, Dunaliella salina undergoes significant metabolic shifts, while Dunaliella tertiolecta primarily focuses on acclimation in photosynthesis. This metabolic contrast may explain the β‐carotene hyperaccumulation by redirecting carbon from growth to carotenoid metabolism shown in D. salina. [ABSTRACT FROM AUTHOR]

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Summary: Photosynthetic eukaryotes require the proper assembly of photosystem II (PSII) in order to strip electrons from water and fuel carbon fixation reactions. In Arabidopsis thaliana, one of the PSII subunits (CP43/PsbC) was suggested to be assembled into the PSII complex via its interaction with an auxiliary protein called Low PSII Accumulation 2 (LPA2). However, the original articles describing the role of LPA2 in PSII assembly have been retracted. To investigate the function of LPA2 in the model organism for green algae, Chlamydomonas reinhardtii, we generated knockout lpa2 mutants by using the CRISPR‐Cas9 target‐specific genome editing system. Biochemical analyses revealed the thylakoidal localization of LPA2 protein in the wild type (WT), whereas lpa2 mutants were characterized by a drastic reduction in the levels of D1, D2, CP47 and CP43 proteins. Consequently, reduced PSII supercomplex accumulation, chlorophyll content per cell, PSII quantum yield and photosynthetic oxygen evolution were measured in the lpa2 mutants, leading to the almost complete impairment of photoautotrophic growth. Pulse‐chase experiments demonstrated that the absence of LPA2 protein caused reduced PSII assembly and reduced PSII turnover. Taken together, our data indicate that, in C. reinhardtii, LPA2 is required for PSII assembly and proper function. Significance Statement: LPA2 is a nuclear‐encoded protein that is suggested to be involved in PSII assembly in vascular plants. Here, using CRISPSRS/CAS9 mutagenesis, we identified and investigated an LPA2 homolog in Chlamydomonas reinhardtii. lpa2 mutants were characterized by a strong reduction in the accumulation of photosystem II core subunits, reduced photosystem II activity, increased photosensitivity and impairment in photoautotrophic growth, revealing the critical role of LPA2 in the assembly of photosystem II supercomplexes in green algae. [ABSTRACT FROM AUTHOR]

Photosystems must balance between light harvesting to fuel the photosynthetic process for CO2 fixation and mitigating the risk of photodamage due to absorption of light energy in excess. Eukaryotic photosynthetic organisms evolved an array of pigment‐binding proteins called light harvesting complexes constituting the external antenna system in the photosystems, where both light harvesting and activation of photoprotective mechanisms occur. In this work, the balancing role of CP29 and CP26 photosystem II antenna subunits was investigated in Chlamydomonas reinhardtii using CRISPR‐Cas9 technology to obtain single and double mutants depleted of monomeric antennas. Absence of CP26 and CP29 impaired both photosynthetic efficiency and photoprotection: Excitation energy transfer from external antenna to reaction centre was reduced, and state transitions were completely impaired. Moreover, differently from higher plants, photosystem II monomeric antenna proteins resulted to be essential for photoprotective thermal dissipation of excitation energy by nonphotochemical quenching. The functional role of the Photosystem II monomeric antenna complexes CP29 and CP26 was investigated in Chlamydomonas reinhardtii generating single and double mutants by CRISPR‐Cas9 genome editing demonstrating their key role in non‐photochemical quenching of both Photosystem I and II. [ABSTRACT FROM AUTHOR]

Abstract: Lutein and zeaxanthin are dietary carotenoids reported to be protective against age‐related macular degeneration. Recently, the green alga Chlamydomonas reinhardtii has received attention as a photosynthetic cell factory, but the potential of this alga for carotenoid production has not yet been evaluated. In this study, we selected the C. reinhardtii CC‐4349 strain as the best candidate among seven laboratory strains tested for carotenoid production. A knock‐out mutant of the zeaxanthin epoxidase gene induced by preassembled DNA‐free CRISPR‐Cas9 ribonucleoproteins in the CC‐4349 strain had a significantly higher zeaxanthin content (56‐fold) and productivity (47‐fold) than the wild type without the reduction in lutein level. Furthermore, we produced eggs fortified with lutein (2‐fold) and zeaxanthin (2.2‐fold) by feeding hens a diet containing the mutant. Our results clearly demonstrate the possibility of cost‐effective commercial use of microalgal mutants induced by DNA‐free CRISPR‐Cas9 ribonucleoproteins in algal biotechnology for the production of high‐value products. [ABSTRACT FROM AUTHOR]

The quaternary-amino-ethyl 1 ( QAE1) isoforms of type III antifreeze proteins ( AFPs) prevent the growth of ice crystals within organisms living in polar regions. We determined the antifreeze activity of wild-type and mutant constructs of the Japanese notched-fin eelpout ( Zoarces elongates Kner) AFP8 (nfe AFP8) and characterized the structural and dynamics properties of their ice-binding surface using NMR. We found that the three constructs containing the V20G mutation were incapable of stopping the growth of ice crystals and exhibited structural changes, as well as increased conformational flexibility, in the first 310 helix (residues 18-22) of the sequence. Our results suggest that the inactive nfe AFP8s are incapable of anchoring water molecules due to the unusual and flexible backbone conformation of their primary prism plane-binding surface. [ABSTRACT FROM AUTHOR]

Harmful algal blooms ( HABs) can lead to substantial socio-economic losses and extensive damage to aquatic ecosystems, drinking water sources and human health. Common algicidal techniques, including ozonation, ultrasonic treatment and dispersion of algae-killing chemicals, are unsatisfactory both economically and ecologically. This study therefore presents a novel alternative strategy for the efficient control of deleterious algae via the use of host-specific virus-like particles ( VLPs) combined with chemically synthesized algicidal compounds. The capsid protein of HcRNAV34, a single-stranded RNA virus that infects the toxic dinoflagellate, H eterocapsa circularisquama, was expressed in and purified from E scherichia coli and then self-assembled into VLPs in vitro. Next, the algicidal compound, thiazolidinedione 49 ( TD49), was encapsidated into HcRNAV34 VLPs for specific delivery to H . circularisquama. Consequently, HcRNAV34 VLPs demonstrated the same host selectivity as naturally occurring HcRNAV34 virions, while TD49-encapsidated VLPs showed a more potent target-specific algicidal effect than TD49 alone. These results indicate that target-specific VLPs for the delivery of cytotoxic compounds to nuisance algae might provide a safe, environmentally friendly approach for the management of HABs in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Summary Telomerase is a specialized RNA-directed DNA polymerase that adds telomeric repeats onto the ends of linear eukaryotic chromosomes. It was recently reported that the low, basal level of telomerase activity markedly increased at early S-phase of the cell cycle, and auxin further increased the S-phase-specific telomerase activity in tobacco BY-2 cells. In this study we show that abscisic acid (ABA), a phytohormone known to induce the cyclin-dependent protein kinase inhibitor, effectively abolished both the auxin- and S-phase-specific activation of telomerase in a concentration- and time-dependent fashion in synchronized tobacco BY-2 cells. These results suggest that there exists a hormonal cross-talk between auxin and ABA for the regulation of telomerase activity during the cell cycle of tobacco cells. Treatment of synchronized BY-2 cells with the protein kinase inhibitor staurosporine or H-7 effectively prevented the S-phase-specific activation of telomerase activity. By contrast, when okadaic acid or cantharidin, potent inhibitors of protein phosphatase 2A (PP2A), was applied to the cells, the S-phase-specific high level of telomerase activity was continuously maintained in the cell cycle for at least 14 h after release from M-phase arrest. Incubation of tobacco cell extracts with exogenous PP2A rapidly abrogated in vitro telomerase activity, while okadaic acid and cantharidin blocked the action of PP2A, effectively restoring in vitro telomerase activity. Taken together, these findings are discussed in the light of the suggestion that antagonistic functions of auxin and ABA, and reciprocal phosphorylation and dephosphorylation of telomerase complex, are necessarily involved in the cell cycle-dependent modulation of telomerase activity in tobacco cells. [ABSTRACT FROM AUTHOR]