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Dunaliella salina is an innovative expression system due to its distinct advantages such as high salt tolerance, low susceptibility to contamination, and the absence of the cell wall. While nuclear transformation has been extensively studied, research on D. salina chloroplast transformation remains in the preliminary stages. In this study, we established an efficient chloroplast expression system for D. salina using Golden Gate assembly. We developed a D. salina toolkit comprising essential components such as chloroplast-specific promoters, terminators, homologous fragments, and various vectors. We confirmed its functionality by expressing the EGFP protein. Moreover, we detailed the methodology of the entire construction process. This expression system enables the specific targeting of foreign genes through simple homologous recombination, resulting in stable expression in chloroplasts. The toolkit achieved a relatively high transformation efficiency within a shorter experimental cycle. Consequently, the construction and utilization of this toolkit have the potential to enhance the efficiency of transgenic engineering in D. salina and advance the development of microalgal biofactories., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Astaxanthin is a naturally occurring xanthophyll with powerful: antioxidant, antitumor, and antibacterial properties that are widely employed in food, feed, medicinal and nutraceutical industries. Currently, chemical synthesis dominates the world's astaxanthin market, but the increasing demand for natural products is shifting the market for natural astaxanthin. Haematococcus pluvialis (H. pluvialis) is the factory source of natural astaxanthin when grown in optimal conditions. Currently, various strategies for the production of astaxanthin have been proposed or are being developed in order to meet its market demand. This up-to-date review scrutinized the current approaches or strategies that aim to increase astaxanthin yield from H. pluvialis . We have emphasized the genetic and environmental parameters that increase astaxanthin yield. We also looked at the transcriptomic dynamics caused by environmental factors (phytohormones induction, light, salt, temperature, and nutrient starvation) on astaxanthin synthesizing genes and other metabolic changes. Genetic engineering and culture optimization (environmental factors) are effective approaches to producing more astaxanthin for commercial purposes. Genetic engineering, in particular, is accurate, specific, potent, and safer than conventional random mutagenesis approaches. New technologies, such as CRISPR-Cas9 coupled with omics and emerging computational tools, may be the principal strategies in the future to attain strains that can produce more astaxanthin. This review provides accessible data on the strategies to increase astaxanthin accumulation natively. Also, this review can be a starting point for new scholars interested in H. pluvialis research.

Nucleotide-binding leucine-rich repeat (NLR) proteins are crucial intracellular immune receptors in plants, responsible for detecting invading pathogens and initiating defense responses. While previous studies on the evolution and function of NLR genes were mainly limited to land plants, the evolutionary trajectory and immune-activating character of NLR genes in algae remain less explored. In this study, genome-wide NLR gene analysis was conducted on 44 chlorophyte species across seven classes and seven charophyte species across five classes. A few but variable number of NLR genes, ranging from one to 20, were identified in five chlorophytes and three charophytes, whereas no NLR gene was identified from the remaining algal genomes. Compared with land plants, algal genomes possess fewer or usually no NLR genes, implying that the expansion of NLR genes in land plants can be attributed to their adaptation to the more complex terrestrial pathogen environments. Through phylogenetic analysis, domain composition analysis, and conserved motifs profiling of the NBS domain, we detected shared and lineage-specific features between NLR genes in algae and land plants, supporting the common origin and continuous evolution of green plant NLR genes. Immune-activation assays revealed that both TNL and RNL proteins from green algae can elicit hypersensitive responses in Nicotiana benthamiana, indicating the molecular basis for immune activation has emerged in the early evolutionary stage of different types of NLR proteins. In summary, the results from this study suggest that NLR proteins may have taken a role as intracellular immune receptors in the common ancestor of green plants., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Desmodesmus spp. are one of the most dominant components of phytoplankton, which are present in most water bodies. However, identification of the species based only on morphological data is challenging. The aim of the present study was to provide a comprehensive understanding of the actual distribution of the Desmodesmus species in Saga City, Saga Prefecture, Japan. In the present study, 38 water bodies were surveyed between June 2017 and March 2023. A total of 86 culture strains were established from the samples collected from the 21 sites, and identified by molecular phylogenetic analysis, comparison of ITS2 rRNA secondary structures, and observation of surface microstructure. In total, four new species, including D. notatus Demura sp. nov., D. lamellatus Demura sp. nov., D. fragilis Demura sp. nov., and D. reticulatus Demura sp. nov. were proposed and 17 Desmodesmus species were identified as described species. The present study revealed > 20 Desmodesmus species, exhibiting high genetic diversity in a small area., (© 2024. The Author(s).)

Optogenetics, the method of light-controlled regulation of cellular processes is based on the use of the channelrhodopsins that directly generate photoinduced currents. Most of the channelrhodopsin genes have been identified in the green microalgae Chlorophyta, and the demand for increasing the number of functionally characterized channelrhodopsins and the diversity of their photochemical parameters keeps growing. We performed the expression analysis of cation channelrhodopsin (CCR) genes in natural isolates of microalgae of the genera Haematococcus and Bracteacoccus from the unique Arctic Circle region. The identified full-length CCR transcript of H. lacustris is the product of alternative splicing and encodes the Hl98CCR2 protein with no photochemical activity. The 5'-partial fragment of the B. aggregatus CCR transcript encodes the Ba34CCR protein containing a conserved TM1-TM7 membrane domain and a short cytosolic fragment. Upon heterologous expression of the TM1-TM7 fragment in CHO-K1 cell culture, light-dependent current generation was observed with the parameters corresponding to those of the CCR. The first discovered functional channelrhodopsin of Bracteacoccus has no close CCR homologues and may be of interest as a candidate for optogenetics.

Photostasis is the light-dependent maintenance of energy balance associated with cellular homeostasis in photoautotrophs. We review evidence that illustrates how photosynthetic adaptation in polar photoautrophs such as aquatic green algae, cyanobacteria, boreal conifers as well as terrestrial angiosperms exhibit an astonishing plasticity in structure and function of the photosynthetic apparatus. This plasticity contributes to the maintenance of photostasis, which is essential for the long-term survival in the seemingly inhospitable Antarctic and Arctic habitats. However, evidence indicates that polar photoautrophic species exhibit different functional solutions for the maintenance of photostasis. We suggest that this reflects, in part, the genetic diversity symbolized by inherent genetic redundancy characteristic of polar photoautotrophs which enhances their survival in a thermodynamically challenging environment., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The marine prasinophyte green algae Pycnococcus provasolii and Pseudoscourfieldia marina represent the only extant genera and known species of the Pycnococcaceae. However, their taxonomic status needs to be reassessed, owing to the very close relationship inferred from previous sequence comparisons of individual genes. Although Py. provasolii and Ps. marina are morphologically different, their plastid rbcL and nuclear small subunit rRNA genes were observed to be nearly or entirely identical in sequence, thus leading to the hypothesis that they represent distinct growth forms or alternate life-cycle stages of the same organism. To evaluate this hypothesis, we used organelle genomes as molecular markers. The plastome and mitogenome of Ps. marina UIO 007 were sequenced and compared with those available for two isolates of Py. provasolii (CCMP 1203 and CCAP 190/2). The Ps. marina organelle genomes proved to be almost identical in size and had the same gene content and gene order as their Py. provasolii counterparts. Single nucleotide substitutions and insertions/deletions were localized using genome-scale sequence alignments. Over 99.70% sequence identities were observed in all pairwise comparisons of plastomes and mitogenomes. Alignments of both organelle genomes revealed that Ps. marina UIO 007 is closer to Py. provasolii CCAP 190/2 than are the two Py. provasolii strains to one another. Therefore, our results are not consistent with the placement of Ps. marina and Py. provasolii strains into distinct genera. We propose a taxonomic revision of the Pycnococcaceae and the erection of a new class of Chlorophyta, the Pseudoscourfieldiophyceae., (© 2024 The Author(s). Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

The colonial green microalga Botryococcus braunii is well known for producing liquid hydrocarbons that can be utilized as biofuel feedstocks. B. braunii is taxonomically classified as a single species made up of three chemical races, A, B, and L, that are mainly distinguished by the hydrocarbons produced. We previously reported a B race draft nuclear genome, and here we report the draft nuclear genomes for the A and L races. A comparative genomic study of the three B. braunii races and 14 other algal species within Chlorophyta revealed significant differences in the genomes of each race of B. braunii. Phylogenomically, there was a clear divergence of the three races with the A race diverging earlier than both the B and L races, and the B and L races diverging from a later common ancestor not shared by the A race. DNA repeat content analysis suggested the B race had more repeat content than the A or L races. Orthogroup analysis revealed the B. braunii races displayed more gene orthogroup diversity than three closely related Chlamydomonas species, with nearly 24-36% of all genes in each B. braunii race being specific to each race. This analysis suggests the three races are distinct species based on sufficient differences in their respective genomes. We propose reclassification of the three chemical races to the following species names: Botryococcus alkenealis (A race), Botryococcus braunii (B race), and Botryococcus lycopadienor (L race)., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Boland et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Energy status and nutrients regulate photosynthetic protein expression. The unicellular green alga Chromochloris zofingiensis switches off photosynthesis in the presence of exogenous glucose (+Glc) in a process that depends on hexokinase (HXK1). Here, we show that this response requires that cells lack sufficient iron (-Fe). Cells grown in -Fe+Glc accumulate triacylglycerol (TAG) while losing photosynthesis and thylakoid membranes. However, cells with an iron supplement (+Fe+Glc) maintain photosynthesis and thylakoids while still accumulating TAG. Proteomic analysis shows that known photosynthetic proteins are most depleted in heterotrophy, alongside hundreds of uncharacterized, conserved proteins. Photosynthesis repression is associated with enzyme and transporter regulation that redirects iron resources to (a) respiratory instead of photosynthetic complexes and (b) a ferredoxin-dependent desaturase pathway supporting TAG accumulation rather than thylakoid lipid synthesis. Combining insights from diverse organisms from green algae to vascular plants, we show how iron and trophic constraints on metabolism aid gene discovery for photosynthesis and biofuel production., (© 2024. The Author(s).)

Snow algae are a diverse group of extremophilic microeukaryotes found on melting polar and alpine snowfields. They play an important role in the microbial ecology of the cryosphere, and their propagation on snow and ice surfaces may in part accelerate climate-induced melting of these systems. High-quality snow algae genomes are needed for studies on their unique physiology, adaptive mechanisms, and genome evolution under multiple forms of stress, including cold temperatures and intense sunlight. Here, we assembled and annotated the genome of Limnomonas spitsbergensis, a cryophilic biciliate green alga originally isolated from melting snow on Svalbard, in the Arctic. The L. spitsbergensis genome assembly is based primarily on the use of PacBio long reads and secondly Illumina short reads, with an assembly size of 260.248 Mb in 124 contigs. A combination of 3 alternative annotation strategies was used including protein homology, RNA-seq evidence, and PacBio full-length transcript isoforms. The best merged set of annotations identified 18,277 protein-coding genes, which were 95.2% complete based on Benchmarking Universal Single-Copy Orthologs analysis. We also provide the annotated mitogenome, which is a relatively large 77.942 kb circular mapping sequence containing extensive repeats. The L. spitsbergensis genome will provide a new resource for research on snow algae adaptation, behavior, and natural selection in unique, low-temperature terrestrial environments that are under threat from climate change., Competing Interests: Conflicts of interest The authors declare no conflicts of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Genetics Society of America.)

Steroid estrogens (SEs) have garnered global attention because of their potential hazards to human health and aquatic organisms at low concentrations (ng/L). The ecosystems of plateau freshwater lakes are fragile, the water lag time is long, and pollutants easily accumulate, making them more vulnerable to the impact of SEs. However, the knowledge of the impact of SEs on the growth and decomposition of phytoplankton communities in plateau lakes and the eutrophication process is limited. This study investigated the effects and mechanisms of SEs exposure on dominant algal communities and the expression of typical algal functional genes in Erhai Lake using indoor simulations and molecular biological methods. The results showed that phytoplankton were sensitive to 17β-estradiol (E2β) pollution, with a concentration of 50, and 100 ng/L E2β exposure promoting the growth of cyanophyta and chlorophyta in the short term; this poses an ecological risk of inducing algal blooms. E2β of 1000 ng/L exposure led to cross-effects of estrogenic effects and toxicity, with most phytoplankton being inhibited. However, small filamentous cyanobacteria and diatoms exhibited greater tolerance; Melosira sp. even exhibited "low inhibition, high promotion" behavior. Exposure to E2β reduced the Shannon-Wiener diversity index (H'), Pielou index (J), and the number of dominant algal species (S) in phytoplankton communities, leading to instability in community succession. E2β of 50 ng/L enhanced the expression levels of relevant functional genes, such as ftsH, psaB, atpB, and prx, related to Microcystis aeruginosa. E2β of 50 ng/L and 5 mg/L can promote the transcription of Microcystis toxins (MC) related genes (mcyA), leading to more MC production by algal cells., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The green algae of the genus Ancylonema, which belong to the zygnematophytes, are prevalent colonizers of glaciers worldwide. They display a striking reddish-brown pigmentation in their natural environment, due to vacuolar compounds related to gallic acid. This pigmentation causes glacier darkening when these algae bloom, leading to increased melting rates. The Ancylonema species known so far are true psychrophiles, which hinders experimental work and limits our understanding of these algae. For instance, the biosynthesis, triggering factors, and biological function of Ancylonema's secondary pigments remain unknown. In this study, we introduce a mesophilic Ancylonema species, A. palustre sp. nov., from temperate moorlands. This species forms the sister lineage to all known psychrophilic strains. Despite its morphological similarity to the latter, it exhibits unique autecological and photophysiological characteristics. It allows us to describe vegetative and sexual cellular processes in great detail. We also conducted experimental tests for abiotic factors that induce the secondary pigments of zygnematophytes. We found that low nutrient conditions combined with ultraviolet B radiation result in vacuolar pigmentation, suggesting a sunscreen function. Our thriving, bacteria-free cultures of Ancylonema palustre will enable comparative genomic studies of mesophilic and extremophilic zygnematophytes. These studies may provide insights into how Ancylonema species colonized the world's glaciers., (© 2024 The Author(s). Environmental Microbiology published by John Wiley & Sons Ltd.)

Green feather algae (Bryopsidales) undergo a unique life cycle in which a single cell repeatedly executes nuclear division without cytokinesis, resulting in the development of a thallus (>100 mm) with characteristic morphology called coenocyte. Bryopsis is a representative coenocytic alga that has exceptionally high regeneration ability: extruded cytoplasm aggregates rapidly in seawater, leading to the formation of protoplasts. However, the genetic basis of the unique cell biology of Bryopsis remains poorly understood. Here, we present a high-quality assembly and annotation of the nuclear genome of Bryopsis sp. (90.7 Mbp, 27 contigs, N50 = 6.7 Mbp, 14 034 protein-coding genes). Comparative genomic analyses indicate that the genes encoding BPL-1/Bryohealin, the aggregation-promoting lectin, are heavily duplicated in Bryopsis, whereas homologous genes are absent in other ulvophyceans, suggesting the basis of regeneration capability of Bryopsis. Bryopsis sp. possesses >30 kinesins but only a single myosin, which differs from other green algae that have multiple types of myosin genes. Consistent with this biased motor toolkit, we observed that the bidirectional motility of chloroplasts in the cytoplasm was dependent on microtubules but not actin in Bryopsis sp. Most genes required for cytokinesis in plants are present in Bryopsis, including those in the SNARE or kinesin superfamily. Nevertheless, a kinesin crucial for cytokinesis initiation in plants (NACK/Kinesin-7II) is hardly expressed in the coenocytic part of the thallus, possibly underlying the lack of cytokinesis in this portion. The present genome sequence lays the foundation for experimental biology in coenocytic macroalgae., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Marine microbes are important in biogeochemical cycling, but the nature and magnitude of their contributions are influenced by their associated viruses. In the presence of a lytic virus, cells that have evolved resistance to infection have an obvious fitness advantage over relatives that remain susceptible. However, susceptible cells remain extant in the wild, implying that the evolution of a fitness advantage in one dimension (virus resistance) must be accompanied by a fitness cost in another dimension. Identifying costs of resistance is challenging because fitness is context-dependent. We examined the context dependence of fitness costs in isolates of the picophytoplankton genus Micromonas and their co-occurring dsDNA viruses using experimental evolution. After generating 88 resistant lineages from two ancestral Micromonas strains, each challenged with one of four distinct viral strains, we found resistance led to a 46% decrease in mean growth rate under high irradiance and a 19% decrease under low. After a year in culture, the experimentally selected lines remained resistant, but fitness costs had attenuated. Our results suggest that the cost of resistance in Micromonas is dependent on environmental conditions and the duration of population adaptation, illustrating the dynamic nature of fitness costs of viral resistance among marine protists., (© 2024 John Wiley & Sons Ltd.)

Light management strategy is crucial for improving microalgal production in terms of higher biomass and economically valuable bioactive molecules. However, green light has received less attention in developing light managements for algae and higher plant due to its low absorption rate by chlorophyll. In this study, the effects of green light supplementation, in the combination with red and blue light were investigated in Haematococcus pluvialis. 10% and 20% of green light supplementations were applied in 3:2 ratios of red and blue LED light combinations as an expense of red-light. Growth rates, chlorophyll concentration, and dry weight were measured to assess the growth kinetics of H. pluvialis along with the relative transcript accumulations of four mRNAs: Rubisco, PTOX 2 , PsaB, and PsbS. Growth rates, chlorophyll concentrations and dry weight were found significantly higher in presence of 10% green light supplementation compared to red and blue light combinations. The relative transcript accumulations of Rubisco and PsbS genes showed significant upregulation at the end of the experiments (with the fold change of 42.91 ± 12.08 and 98.57 ± 27.38, respectively, relative to the beginning of the experiments) compared to combinations of red and blue light (fold change of 19.09 ± 3.0 and 47.77 ± 14.21, respectively, relative to beginning of the experiments). PsaB and PTOX 2 transcripts did not show significant accumulation differences between treatments. It seems that green light has a dose dependent additive effect on the growth rate of H. pluvialis. The upregulation of Rubisco and PsbS may indicate green light dependent carbon assimilation and light-harvesting response in H. pluvialis., (© 2024 American Institute of Chemical Engineers.)

Cadmium (Cd) has become a severe issue in relatively low concentration and attracts expert attention due to its toxicity, accumulation, and biomagnification in living organisms. Cd does not have a biological role and causes serious health issues. Therefore, Cd pollutants should be reduced and removed from the environment. Microalgae have great potential for Cd absorption for waste treatment since they are more environmentally friendly than existing treatment methods and have strong metal sorption selectivity. This study evaluated the tolerance and ability of the microalga Tetratostichococcus sp. P1 to remove Cd ions under acidic conditions and reveal mechanisms based on transcriptomics analysis. The results showed that Tetratostichococcus sp. P1 had a high Cd tolerance that survived under the presence of Cd up to 100 µM, and IC 50 , the half-maximal inhibitory concentration value, was 57.0 μM, calculated from the change in growth rate based on the chlorophyll content. Long-term Cd exposure affected the algal morphology and photosynthetic pigments of the alga. Tetratostichococcus sp. P1 removed Cd with a maximum uptake of 1.55 mg g -1 dry weight. Transcriptomic analysis revealed the upregulation of the expression of genes related to metal binding, such as metallothionein. Group A, Group B transporters and glutathione, were also found upregulated. While the downregulation of the genes were related to photosynthesis, mitochondria electron transport, ABC-2 transporter, polysaccharide metabolic process, and cell division. This research is the first study on heavy metal bioremediation using Tetratostichococcus sp. P1 and provides a new potential microalga strain for heavy metal removal in wastewater.[Figure: see text] Abbreviations: BP: Biological process; bZIP: Basic Leucine Zipper; CC: Cellular component; ccc1: Ca (II)-sensitive cross complementary 1; Cd: Cadmium; CDF: Cation diffusion facilitator; Chl: Chlorophyll; CTR: Cu TRansporter families; DAGs: Directed acyclic graphs; DEGs: Differentially expressed genes; DVR: Divinyl chlorophyllide, an 8-vinyl-reductase; FPN: FerroportinN; FTIR: Fourier transform infrared; FTR: Fe TRansporter; GO: Gene Ontology; IC50: Growth half maximal inhibitory concentration; ICP: Inductively coupled plasma; MF: molecular function; NRAMPs: Natural resistance-associated aacrophage proteins; OD: Optical density; RPKM: Reads Per Kilobase of Exon Per Million Reads Mapped; VIT1: Vacuolar iron transporter 1 families; ZIPs: Zrt-, Irt-like proteins.

Green algae usually assigned to the genus Oophila are known to colonize egg capsules of amphibian egg masses across the Nearctic and Palearctic regions. We study the phylogenetic relationships of these algae using a phylotranscriptomic data set of 76 protein-coding single-copy nuclear genes. Our data set includes novel RNAseq data for six amphibian-associated and five free-living green algae, and draft genomes of two of the latter. Within the Oophila clade (nested within Moewusinia), we find samples from two European frogs (Rana dalmatina and R. temporaria) closely related to those of the North American frog R. aurora (Oophila subclade III). An isolate from the North American R. sylvatica (subclade IV) appears to be sister to the Japanese isolate from the salamander Hynobius nigrescens (subclade J1), and subclade I algae from Ambystoma maculatum are sister to all other lineages in the Oophila clade. Two free-living algae (Chlamydomonas nasuta and Cd. pseudogloeogama) are nested within the Oophila clade, and a strain of the type species of Chlorococcum (Cc. infusionum) is related to this assemblage. Our phylotranscriptomic tree suggests that recognition of different species within the Oophila clade ("clade B" of earlier studies) is warranted, and calls for a comprehensive taxonomic revision of Moewusinia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Chromochloris zofingiensis , a unicellular green alga, is a potential source of natural carotenoids. In this study, the mutant LUT-4 was acquired from the chemical mutagenesis pool of C. zofingiensis strain. The biomass yield and lutein content of LUT-4 reached 9.23 g·L -1 , and 0.209% of dry weight (DW) on Day 3, which was 49.4%, and 33% higher than that of wild-type (WT), respectively. The biomass yields of LUT-4 under 100, 300, and 500 µmol/m 2 /s reached 8.4 g·L -1 , 7.75 g·L -1 , and 6.6 g·L -1 , which was 10.4%, 21%, and 29.6% lower compared with the control, respectively. Under mixotrophic conditions, the lutein yields were significantly higher than that obtained in the control. The light intensity of 300 µmol/m 2 /s was optimal for lutein biosynthesis and the content of lutein reached 0.294% of DW on Day 3, which was 40.7% more than that of the control. When LUT-4 was grown under 300 µmol/m 2 /s, a significant increase in expression of genes implicated in lutein biosynthesis, including phytoene synthase ( PSY ), phytoene desaturase ( PDS ), and lycopene epsilon cyclase ( LCYe ) was observed. The changes in biochemical composition, Ace-CoA, pyruvate, isopentenyl pyrophosphate (IPP), and geranylgeranyl diphosphate (GGPP) contents during lutein biosynthesis were caused by utilization of organic carbon. It was thereby concluded that 300 µmol/m 2 /s was the optimal culture light intensity for the mutant LUT-4 to synthesize lutein. The results would be helpful for the large-scale production of lutein.

Sphingolipids (SLs) are ubiquitous components of eukaryotic cell membranes and are found in some prokaryotic organisms and viruses. They are composed of a sphingoid backbone that may be acylated and glycosylated. Assembly of various sphingoid base, fatty acyl and glycosyl moieties results in highly diverse structures. The functional significance of variations in SL chemical diversity and abundance is still in the early stages of investigation. Among SL modifications, Δ8-desaturation of the sphingoid base occurs only in plants and fungi. In plants, SL Δ8-unsaturation is involved in cold hardiness. Our knowledge of the structure and functions of SLs in microalgae lags far behind that of animals, plants and fungi. Original SL structures have been reported from microalgae. However, functional studies are still missing. Ostreococcus tauri is a minimal microalga at the base of the green lineage and is therefore a key organism for understanding lipid evolution. In the present work, we achieved the detailed characterization of O. tauri SLs and unveiled unique glycosylceramides as sole complex SLs. The head groups are reminiscent of bacterial SLs, as they contain hexuronic acid residues and can be polyglycosylated. Ceramide backbones show a limited variety, and SL modification is restricted to Δ8-unsaturation. The Δ8-SL desaturase from O. tauri only produced E isomers. Expression of both Δ8-SL desaturase and Δ8-unsaturation of sphingolipids varied with temperature, with lower levels at 24°C than at 14°C. Overexpression of the Δ8-SL desaturase dramatically increases the level of Δ8 unsaturation at 24°C and is paralleled by a failure to increase cell size. Our work provides the first characterization of O. tauri SLs and functional evidence for the involvement of SL Δ8-unsaturation for temperature acclimation in microalgae, suggesting that this function is an ancestral feature in the green lineage., (© The Author(s) 2024. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In flowering plants, euchromatic transposons are transcriptionally silenced by RNA-directed DNA Methylation, a small RNA-guided de novo methylation pathway. RNA-directed DNA Methylation requires the activity of the RNA Polymerases IV and V, which produce small RNA precursors and noncoding targets of small RNAs, respectively. These polymerases are distinguished from Polymerase II by multiple plant-specific paralogous subunits. Most RNA-directed DNA Methylation components are present in all land plants, and some have been found in the charophytic green algae, a paraphyletic group that is sister to land plants. However, the evolutionary origin of key RNA-directed DNA Methylation components, including the two largest subunits of Polymerase IV and Polymerase V, remains unclear. Here, we show that multiple lineages of charophytic green algae encode a single-copy precursor of the largest subunits of Polymerase IV and Polymerase V, resolving the two presumed duplications in this gene family. We further demonstrate the presence of a Polymerase V-like C-terminal domain, suggesting that the earliest form of RNA-directed DNA Methylation utilized a single Polymerase V-like polymerase. Finally, we reveal that charophytic green algae encode a single CLSY/DRD1-type chromatin remodeling protein, further supporting the presence of a single specialized polymerase in charophytic green algae., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

Ostreococcus spp. are unicellular organisms with one of the simplest cellular organizations. The sequencing of the genomes of different Ostreococcus species has reinforced this status since Ostreococcus tauri has one most compact nuclear genomes among eukaryotic organisms. Despite this, it has retained a number of genes, setting it apart from other organisms with similar small genomes. Ostreococcus spp. feature a substantial number of selenocysteine-containing proteins, which, due to their higher catalytic activity compared to their selenium-lacking counterparts, may require a reduced quantity of proteins. Notably, O. tauri encodes several ammonium transporter genes, that may provide it with a competitive edge for acquiring nitrogen (N). This characteristic makes it an intriguing model for studying the efficient use of N in eukaryotes. Under conditions of low N availability, O. tauri utilizes N from abundant proteins or amino acids, such as L-arginine, similar to higher plants. However, the presence of a nitric oxide synthase (L-arg substrate) sheds light on a new metabolic pathway for L-arg in algae. The metabolic adaptations of O. tauri to day and night cycles offer valuable insights into carbon and iron metabolic configuration. O. tauri has evolved novel strategies to optimize iron uptake, lacking the classic components of the iron absorption mechanism. Overall, the cellular and genetic characteristics of Ostreococcus contribute to its evolutionary success, making it an excellent model for studying the physiological and genetic aspects of how green algae have adapted to the marine environment. Furthermore, given its potential for lipid accumulation and its marine habitat, it may represent a promising avenue for third-generation biofuels., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Dunaliella salina, a microalga that thrives under high-saline conditions, is notable for its high β-carotene content and the absence of a polysaccharide cell wall. These unique characteristics render it a prime candidate as a cellular platform for astaxanthin production. In this study, our initial tests in an E. coli revealed that β-ring-4-dehydrogenase (CBFD) and 4-hydroxy-β-ring-4-dehydrogenase (HBFD) genes from Adonis aestivalis outperformed β-carotene hydroxylase (BCH) and β-carotene ketolase (BKT) from Haematococcus pluvialis counterparts by two-fold in terms of astaxanthin biosynthesis efficiency. Subsequently, we utilized electroporation to integrate either the BKT gene or the CBFD and HBFD genes into the genome of D. salina. In comparison to wild-type D. salina, strains transformed with BKT or CBFD and HBFD exhibited inhibited growth, underwent color changes to shades of red and yellow, and saw a nearly 50% decline in cell density. HPLC analysis confirmed astaxanthin synthesis in engineered D. salina strains, with CBFD + HBFD-D. salina yielding 134.88 ± 9.12 μg/g of dry cell weight (DCW), significantly higher than BKT-D. salina (83.58 ± 2.40 μg/g). This represents the largest amount of astaxanthin extracted from transgenic D. salina, as reported to date. These findings have significant implications, opening up new avenues for the development of specialized D. salina-based microcell factories for efficient astaxanthin production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Marine biogeochemical cycles are built on interactions between surface ocean microbes, particularly those connecting phytoplankton primary producers to heterotrophic bacteria. Details of these associations are not well understood, especially in the case of direct influences of bacteria on phytoplankton physiology. Here we catalogue how the presence of three marine bacteria (Ruegeria pomeroyi DSS-3, Stenotrophomonas sp. SKA14 and Polaribacter dokdonensis MED152) individually and uniquely impact gene expression of the picoeukaryotic alga Micromonas commoda RCC 299. We find a dramatic transcriptomic remodelling by M. commoda after 8 h in co-culture, followed by an increase in cell numbers by 56 h compared with the axenic cultures. Some aspects of the algal transcriptomic response are conserved across all three bacterial co-cultures, including an unexpected reduction in relative expression of photosynthesis and carbon fixation pathways. Expression differences restricted to a single bacterium are also observed, with the Flavobacteriia P. dokdonensis uniquely eliciting changes in relative expression of algal genes involved in biotin biosynthesis and the acquisition and assimilation of nitrogen. This study reveals that M. commoda has rapid and extensive responses to heterotrophic bacteria in ways that are generalizable, as well as in a taxon specific manner, with implications for the diversity of phytoplankton-bacteria interactions ongoing in the surface ocean., (© 2024 The Author(s). Environmental Microbiology Reports published by John Wiley & Sons Ltd.)

Microalgae are the preferred species for producing astaxanthin because they pose a low toxicity risk than chemical synthesis. Astaxanthin has multiple health benefits and is being used in: medicines, nutraceuticals, cosmetics, and functional foods. Haematococcus pluvialis is a model microalga for astaxanthin biosynthesis; however, its natural astaxanthin content is low. Therefore, it is necessary to develop methods to improve the biosynthesis of astaxanthin to meet industrial demands, making its commercialization cost-effective. Several strategies related to cultivation conditions are employed to enhance the biosynthesis of astaxanthin in H. pluvialis. However, the mechanism of its regulation by transcription factors is unknown. For the first time, this study critically reviewed the studies on identifying transcription factors, progress in H. pluvialis genetic transformation, and use of phytohormones that increase the gene expression related to astaxanthin biosynthesis. In addition, we propose future approaches, including (i) Cloning and characterization of transcription factors, (ii) Transcriptional engineering through overexpression of positive regulators or downregulation/silencing of negative regulators, (iii) Gene editing for enrichment or deletion of transcription factors binding sites, (iv) Hormonal modulation of transcription factors. This review provides considerable knowledge about the molecular regulation of astaxanthin biosynthesis and the existing research gap. Besides, it provides the basis for transcription factors mediated metabolic engineering of astaxanthin biosynthesis in H. pluvialis .

Mutualistic symbioses have contributed to major transitions in the evolution of life. Here, we investigate the evolutionary history and the molecular innovations at the origin of lichens, which are a symbiosis established between fungi and green algae or cyanobacteria. We de novo sequence the genomes or transcriptomes of 12 lichen algal symbiont (LAS) and closely related non-symbiotic algae (NSA) to improve the genomic coverage of Chlorophyte algae. We then perform ancestral state reconstruction and comparative phylogenomics. We identify at least three independent gains of the ability to engage in the lichen symbiosis, one in Trebouxiophyceae and two in Ulvophyceae, confirming the convergent evolution of the lichen symbioses. A carbohydrate-active enzyme from the glycoside hydrolase 8 (GH8) family was identified as a top candidate for the molecular-mechanism underlying lichen symbiosis in Trebouxiophyceae. This GH8 was acquired in lichenizing Trebouxiophyceae by horizontal gene transfer, concomitantly with the ability to associate with lichens fungal symbionts (LFS) and is able to degrade polysaccharides found in the cell wall of LFS. These findings indicate that a combination of gene family expansion and horizontal gene transfer provided the basis for lichenization to evolve in chlorophyte algae., (© 2024. The Author(s).)

Background: Dark pigmented snow and glacier ice algae on glaciers and ice sheets contribute to accelerating melt. The biological controls on these algae, particularly the role of viruses, remain poorly understood. Giant viruses, classified under the nucleocytoplasmic large DNA viruses (NCLDV) supergroup (phylum Nucleocytoviricota), are diverse and globally distributed. NCLDVs are known to infect eukaryotic cells in marine and freshwater environments, providing a biological control on the algal population in these ecosystems. However, there is very limited information on the diversity and ecosystem function of NCLDVs in terrestrial icy habitats., Results: In this study, we investigate for the first time giant viruses and their host connections on ice and snow habitats, such as cryoconite, dark ice, ice core, red and green snow, and genomic assemblies of five cultivated Chlorophyta snow algae. Giant virus marker genes were present in almost all samples; the highest abundances were recovered from red snow and the snow algae genomic assemblies, followed by green snow and dark ice. The variety of active algae and protists in these GrIS habitats containing NCLDV marker genes suggests that infection can occur on a range of eukaryotic hosts. Metagenomic data from red and green snow contained evidence of giant virus metagenome-assembled genomes from the orders Imitervirales, Asfuvirales, and Algavirales., Conclusion: Our study highlights NCLDV family signatures in snow and ice samples from the Greenland ice sheet. Giant virus metagenome-assembled genomes (GVMAGs) were found in red snow samples, and related NCLDV marker genes were identified for the first time in snow algal culture genomic assemblies; implying a relationship between the NCLDVs and snow algae. Metatranscriptomic viral genes also aligned with metagenomic sequences, suggesting that NCLDVs are an active component of the microbial community and are potential "top-down" controls of the eukaryotic algal and protistan members. This study reveals the unprecedented presence of a diverse community of NCLDVs in a variety of glacial habitats dominated by algae., (© 2024. The Author(s).)

Animal regeneration involves coordinated responses across cell types throughout the animal body. In endosymbiotic animals, whether and how symbionts react to host injury and how cellular responses are integrated across species remain unexplored. Here, we study the acoel Convolutriloba longifissura, which hosts symbiotic Tetraselmis sp. green algae and can regenerate entire bodies from tissue fragments. We show that animal injury causes a decline in the photosynthetic efficiency of the symbiotic algae, alongside two distinct, sequential waves of transcriptional responses in acoel and algal cells. The initial algal response is characterized by the upregulation of a cohort of photosynthesis-related genes, though photosynthesis is not necessary for regeneration. A conserved animal transcription factor, runt, is induced after injury and required for acoel regeneration. Knockdown of Cl-runt dampens transcriptional responses in both species and further reduces algal photosynthetic efficiency post-injury. Our results suggest that the holobiont functions as an integrated unit of biological organization by coordinating molecular networks across species through the runt-dependent animal regeneration program., (© 2024. The Author(s).)

The genomes of charophyte green algae, close relatives of land plants, typically do not show signs of developmental regulation by phytohormones. However, scattered reports of endogenous phytohormone production in these organisms exist. We performed a comprehensive analysis of multiple phytohormones in Viridiplantae, focusing mainly on charophytes. We show that auxin, salicylic acid, ethylene and tRNA-derived cytokinins including cis-zeatin are found ubiquitously in Viridiplantae. By contrast, land plants but not green algae contain the trans-zeatin type cytokinins as well as auxin and cytokinin conjugates. Charophytes occasionally produce jasmonates and abscisic acid, whereas the latter is detected consistently in land plants. Several phytohormones are excreted into the culture medium, including auxin by charophytes and cytokinins and salicylic acid by Viridiplantae in general. We note that the conservation of phytohormone biosynthesis and signaling pathways known from angiosperms does not match the capacity for phytohormone biosynthesis in Viridiplantae. Our phylogenetically guided analysis of established algal cultures provides an important insight into phytohormone biosynthesis and metabolism across Streptophyta., (© 2024. The Author(s).)

Dunaliella bardawil is a marine unicellular green algal that produces large amounts of β-carotene and is a model organism for studying the carotenoid synthesis pathway. However, there are still many mysteries about the enzymes of the D. bardawil lycopene synthesis pathway that have not been revealed. Here, we have identified a CruP-like lycopene isomerase, named DbLyISO, and successfully cloned its gene from D. bardawil . DbLyISO showed a high homology with CruPs. We constructed a 3D model of DbLyISO and performed molecular docking with lycopene, as well as molecular dynamics testing, to identify the functional characteristics of DbLyISO. Functional activity of DbLyISO was also performed by overexpressing gene in both E. coli and D. bardawil . Results revealed that DbLyISO acted at the C-5 and C-13 positions of lycopene, catalyzing its cis - trans isomerization to produce a more stable trans structure. These results provide new ideas for the development of a carotenoid series from engineered bacteria, algae, and plants.

The community structure and co-occurrence pattern of eukaryotic algae in Yuncheng Salt Lake were analyzed based on marker gene analysis of the 18S rRNA V4 region to understand the species composition and their synergistic adaptations to the environmental factors in different salinity waters. The results showed indicated that the overall algal composition of Yuncheng Salt Lake showed a Chlorophyta-Pyrrophyta-Bacillariophyta type structure. Chlorophyta showed an absolute advantage in all salinity waters. In addition, Cryptophyta dominated in the least saline waters; Pyrrophyta and Bacillariophyta were the dominant phyla in the waters with salinity ranging from 13.2 to 18%. Picochlorum, Nannochloris, Ulva, and Tetraselmis of Chlorophyta, Biecheleria and Oxyrrhis of Pyrrophyta, Halamphora, Psammothidium, and Navicula of Bacillariophyta, Guillardia and Rhodomonas of Cryptophyta were not observed in previous surveys of the Yuncheng Salt Lake, suggesting that the algae are undergoing a constant turnover as the water environment of the Salt Lake continues to change. The network diagram demonstrated that the algae were strongly influenced by salinity, NO 3 - , and pH, changes in these environmental factors would lead to changes in the algal community structure, thus affecting the stability of the network structure., (© 2024. The Author(s).)

Symbiomonas scintillans Guillou et Chrétiennot-Dinet, 1999 is a tiny (1.4 μm) heterotrophic microbial eukaryote. The genus was named based on the presence of endosymbiotic bacteria in its endoplasmic reticulum, however, like most such endosymbionts neither the identity nor functional association with its host were known. We generated both amplification-free shotgun metagenomics and whole genome amplification sequencing data from S. scintillans strains RCC257 and RCC24, but were unable to detect any sequences from known lineages of endosymbiotic bacteria. The absence of endobacteria was further verified with FISH analyses. Instead, numerous contigs in assemblies from both RCC24 and RCC257 were closely related to prasinoviruses infecting the green algae Ostreococcus lucimarinus, Bathycoccus prasinos, and Micromonas pusilla (OlV, BpV, and MpV, respectively). Using the BpV genome as a reference, we assembled a near-complete 190 kbp draft genome encoding all hallmark prasinovirus genes, as well as two additional incomplete assemblies of closely related but distinct viruses from RCC257, and three similar draft viral genomes from RCC24, which we collectively call SsVs. A multi-gene tree showed the three SsV genome types branched within highly supported clades with each of BpV2, OlVs, and MpVs, respectively. Interestingly, transmission electron microscopy also revealed a 190 nm virus-like particle similar the morphology and size of the endosymbiont originally reported in S. scintillans. Overall, we conclude that S. scintillans currently does not harbour an endosymbiotic bacterium, but is associated with giant viruses., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Cho et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The unicellular green alga Oophila amblystomatis was named by Lambert in 1905 based upon its association with egg masses of the spotted salamander Ambystoma maculatum. We collected algal cells from Lambert's original egg capsule preparations that were contributed to Phycotheca Boreali-Americana (PBA) in 1905 and subjected them to DNA extraction and PCR with O. amblystomatis-specific 18S rRNA gene primers. DNA amplified from these preparations was cloned and nine clones were sequenced. Along with representative sequences from the Oophila clade and Chlorophyceae, a phylogenetic tree was inferred. Seven sequences clustered within the Oophila clade and two clustered with Chlamydomonas moewusii, which is included in a sister clade to Oophila. By sequencing algal material from the egg capsules of representative type material we can unambiguously characterize O. amblystomatis and define a monophyletic clade centered on this type material. Accordingly, we reject a recent proposal that this species be transferred to Chlorococcum., (© 2024 Phycological Society of America.)

Thick-walled rosette-like snow algae were long thought to be a life stage of various other species of snow algae. Rosette-like cells have not been cultured, but by manually isolating cells from 38 field samples in southern British Columbia, we assigned a variety of rosette morphologies to DNA sequence. Phylogenetic analysis of Rubisco large-subunit (rbcL) gene, ribosomal internal transcribed spacer 2 (ITS2) rRNA region, and 18S rRNA gene revealed that the rosette-like cells form a new clade within the phylogroup Chloromonadinia. Based on these data, we designate a new genus, Rosetta, which comprises five novel species: R. castellata, R. floranivea, R. stellaria, R. rubriterra, and R. papavera. In a survey of 762 snow samples from British Columbia, we observed R. floranivea exclusively on snow overlying high-elevation glaciers, whereas R. castellata was observed at lower elevations, near the tree line. The other three species were rarely observed. Spherical red cells enveloped in a thin translucent sac were conspecific with Rosetta, possibly a developmental stage. These results highlight the unexplored diversity among snow algae and emphasize the utility of single-cell isolation to advance the centuries-old problem of disentangling life stages and cryptic species., (© 2024 The Authors. Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

The diversity of bacteria associated with alpine lichens was profiled. Lichen samples belonging to the Umbilicariaceae family, commonly known as rock tripe lichens, were gathered from two distinct alpine fellfields: one situated on Mt. Brennkogel located in the Eastern European Alps (Austria), and the other on Mt. Stanley located in the Rwenzori mountains of equatorial Africa (Uganda). The primary aim of this research was to undertake a comparative investigation into the bacterial compositions, and diversities, identifying potential indicators and exploring their potential metabolisms, of these lichen samples. Bulk genomic DNA was extracted from the lichen samples, which was used to amplify the 18S rRNA gene by Sanger sequencing and the V3-V4 region of the 16S rRNA gene by Illumina Miseq sequencing. Examination of the fungal partner was carried out through the analysis of 18S rRNA gene sequences, belonging to the genus Umbilicaria (Ascomycota), and the algal partner affiliated with the lineage Trebouxia (Chlorophyta), constituted the symbiotic components. Analyzing the MiSeq datasets by using bioinformatics methods, operational taxonomic units (OTUs) were established based on a predetermined similarity threshold for the V3-V4 sequences, which were assigned to a total of 26 bacterial phyla that were found in both areas. Eight of the 26 phyla, i.e. Acidobacteriota, Actinomycota, Armatimonadota, Bacteroidota, Chloroflexota, Deinococcota, Planctomycetota, and Pseudomonadota, were consistently present in all samples, each accounting for more than 1% of the total read count. Distinct differences in bacterial composition emerged between lichen samples from Austria and Uganda, with the OTU frequency-based regional indicator phyla, Pseudomonadota and Armatimonadota, respectively. Despite the considerable geographic separation of approximately 5430 km between the two regions, the prediction of potential metabolic pathways based on OTU analysis revealed similar relative abundances. This similarity is possibly influenced by comparable alpine climatic conditions prevailing in both areas., (© 2024. The Author(s).)

Pyrenoids are microcompartments that are universally found in the photosynthetic plastids of various eukaryotic algae. They contain ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and play a pivotal role in facilitating CO 2 assimilation via CO 2 -concentrating mechanisms (CCMs). Recent investigations involving model algae have revealed that pyrenoid-associated proteins participate in pyrenoid biogenesis and CCMs. However, these organisms represent only a small part of algal lineages, which limits our comprehensive understanding of the diversity and evolution of pyrenoid-based CCMs. Here we report a pyrenoid proteome of the chlorarachniophyte alga Amorphochlora amoebiformis , which possesses complex plastids acquired through secondary endosymbiosis with green algae. Proteomic analysis using mass spectrometry resulted in the identification of 154 potential pyrenoid components. Subsequent localization experiments demonstrated the specific targeting of eight proteins to pyrenoids. These included a putative Rubisco-binding linker, carbonic anhydrase, membrane transporter, and uncharacterized GTPase proteins. Notably, most of these proteins were unique to this algal lineage. We suggest a plausible scenario in which pyrenoids in chlorarachniophytes have evolved independently, as their components are not inherited from green algal pyrenoids., Competing Interests: Competing interests statement:The authors declare no competing interest.

We report the complete organellar genome sequences of an ultrasmall green alga, Medakamo hakoo strain M-hakoo 311, which has the smallest known nuclear genome in freshwater green algae. Medakamo hakoo has 90.8-kb chloroplast and 36.5-kb mitochondrial genomes containing 80 and 33 putative protein-coding genes, respectively. The mitochondrial genome is the smallest in the Trebouxiophyceae algae studied so far. The GC content of the nuclear genome is 73%, but those of chloroplast and mitochondrial genomes are 41% and 35%, respectively. Codon usages in the organellar genomes have a different tendency from that in the nuclear genome. The organellar genomes have unique characteristics, such as the biased encoding of mitochondrial genes on a single strand and the absence of operon structures in chloroplast ribosomal genes. Medakamo hakoo will be helpful for understanding the evolution of the organellar genome and the regulation of gene expression in chloroplasts and mitochondria.

It is known that co-cultivation of green algae with heterotrophic microorganisms, such as yeast, improves green algae's growth potential and carbon dioxide fixation, even under low CO 2 concentration conditions such as the atmosphere. Introducing mutations into green algae is also expected to enhance their growth potential. In this study, we sought to improve the growth potential of a co-culture system of the green algae Chlamydomonas reinhardtii and the yeast Saccharomyces cerevisiae by introducing mutations into the green algae. Additionally, we performed a transcriptome analysis of the co-culture of the green algae mutant strain with yeast, discussing the interaction between the green algae mutant strain and the yeast. When the green algae mutant strain was co-cultured with yeast, the number of green algae cells reached 152 × 10 5 cells/mL after 7 days of culture. This count was 2.6 times higher than when the wild-type green algae strain was cultured alone and 1.6 times higher than when the wild-type green algae strain and yeast were co-cultured. The transcriptome analysis also indicated that the primary reason for the increased growth potential of the green algae mutant strain was its enhanced photosynthetic activity and nitrogen utilization efficiency., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Complex virus-virus interactions can arise when multiple viruses coinfect the same host, impacting infection outcomes with broader ecological and evolutionary significance for viruses and host. Yet, our knowledge regarding virus competition is still limited, especially for single-celled eukaryotic host-virus systems. Here, we report on mutual interference of two dsDNA viruses, MpoV-45T and MpoV-46T, competing for their Arctic algal host Micromonas polaris. Both viruses affected each other's gene expression and displayed reduced genome replication during coinfection. MpoV-45T was the dominant virus, likely due to interference in the DNA replication of is competitor. Even when its coinfection was delayed, the dominant virus still prevailed while genome production of the other virus was strongly suppressed. This contrasts with typical superinfection exclusion, where the primary infection prevents secondary infection by other viruses. Higher temperature made the suppressed virus a stronger competitor, signifying that global warming is likely to alter virus-virus interactions in Arctic waters., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Microbial Ecology.)

The globin superfamily of proteins is ancient and diverse. Regular assessments based on the increasing number of available genome sequences have elaborated on a complex evolutionary history. In this review, we present a summary of a decade of advances in characterising the globins of cyanobacteria and green algae. The focus is on haem-containing globins with an emphasis on recent experimental developments, which reinforce links to nitrogen metabolism and nitrosative stress response in addition to dioxygen management. Mention is made of globins that do not bind haem to provide an encompassing view of the superfamily and perspective on the field. It is reiterated that an effort toward phenotypical and in-vivo characterisation is needed to elucidate the many roles that these versatile proteins fulfil in oxygenic photosynthetic microbes. It is also proposed that globins from oxygenic organisms are promising proteins for applications in the biotechnology arena., (Copyright © 2024. Published by Elsevier Inc.)

Different marine seaweed species have been shown to harbour specific bacterial communities, however, the extent to which vertical symbiont transmission from parents to offspring contributes to host-specificity is unclear. Here we use fluorescence and electron microscopy as well as 16S rRNA gene-based community analysis to investigate symbiont transmission in members of the three major seaweed groups (green Chlorophyta, red Rhodophyta and brown Phaeophyceae). We found seaweeds employ diverse strategies to transfer symbionts to their progeny. For instance, the green Ulva australis does not appear to have the capacity for vertical transmission. In contrast, the brown Phyllospora comosa adopts a non-selective vertical transmission. The red Delisea pulchra demonstrates weak selectivity in symbiont transmission, while the brown Hormosira banksii exhibits a strongly selective symbiont transfer. Mucilage on the gametes appears to facilitate vertical transmission and transferred bacteria have predicted properties that could support early development of the seaweeds. Previous meta-analysis has indicated that vertical transmission is rare in aquatic compared to terrestrial environments, however, our results contribute to the growing evidence that this might not be the case and that instead vertical transmission with various degrees of symbiont selection occurs in the ecologically important group of seaweeds., (© 2023 The Authors. Environmental Microbiology published by Applied Microbiology International and John Wiley & Sons Ltd.)

Botryococcus braunii, a colonial alga, is known for notably slow growth; however, the growth rate and hydrocarbon productivity are expected to be improved using genetic modification techniques. Nevertheless, B. braunii has a hydrocarbon-rich extracellular matrix (ECM), and the ECM is a major barrier to DNA transformation. To analyse and utilize genetically modified B. braunii, it is essential to regenerate genetically homogeneous colonies derived from single cells. In this study, we developed a novel, simple method for harvesting viable single cells of B. braunii by centrifugation of the culture and subsequent filtration alone. The harvest of single cells was made possible by culturing B. braunii colonies in AF6 medium until the depletion of nitrogen and phosphorus sources and then releasing the single cells in colonies into the medium. Twenty-day culture of single cells in a 96-well plate resulted in 96% regeneration of colonies, and the regeneration of colonies was also confirmed on agar medium. This is the first report of colony regeneration from single cells of B. braunii. We believe that our method developed in this study will contribute greatly to the advancement of genetic modification techniques for B. braunii., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Green algae display a wide range of extracellular matrix (ECM) components that include various types of cell walls (CW), scales, crystalline glycoprotein coverings, hydrophobic compounds, and complex gels or mucilage. Recently, new information derived from genomic/transcriptomic screening, advanced biochemical analyses, immunocytochemical studies, and ecophysiology has significantly enhanced and refined our understanding of the green algal ECM. In the later diverging charophyte group of green algae, the CW and other ECM components provide insight into the evolution of plants and the ways the ECM modulates during environmental stress. Chlorophytes produce diverse ECM components, many of which have been exploited for various uses in medicine, food, and biofuel production. This review highlights major advances in ECM studies of green algae., Competing Interests: Conflict of interest statement. The authors declare that they have no conflict of interests., (© The Author(s) 2023. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Lichen symbiosis is centered around a relationship between a fungus and a photosynthetic microbe, usually a green alga. In addition to their main photosynthetic partner (the photobiont), lichen symbioses can contain additional algae present in low abundance. The biology of these algae and the way they interact with the rest of lichen symbionts remains largely unknown. Here we present the first genome sequence of a non-photobiont lichen-associated alga. Coccomyxa viridis was unexpectedly found in 12% of publicly available lichen metagenomes. With few exceptions, members of the Coccomyxa viridis clade occur in lichens as non-photobionts, potentially growing in thalli endophytically. The 45.7 Mbp genome of C. viridis was assembled into 18 near chromosome-level contigs, making it one of the most contiguous genomic assemblies for any lichen-associated algae. Comparing the C. viridis genome to its close relatives revealed the presence of traits associated with the lichen lifestyle. The genome of C. viridis provides a new resource for exploring the evolution of the lichen symbiosis, and how symbiotic lifestyles shaped evolution in green algae., (© 2023. The Author(s).)

In the present study, a taxonomic review was conducted on representatives of the genus Tetmemorus (Desmidiaceae, Zygnematophyceae) documented within Brazilian territory. This review involved compiling data from the literature and analyzing samples collected throughout the Bahia State, updating our knowledge about this genus in Brazil. For each identified taxon, we provided information such as description, distribution across biomes and states, watersheds, ecological aspects (including habitat and community types), a list of examined (and excluded) materials, and taxonomic comments. Additionally, a taxonomic key for all species reported in Brazil was provided. Through this comprehensive review, we identified a total of eight Tetmemorus taxa occurring in Brazilian territory, comprising five species (T. brebissonii, T. furcatus, T. granulatus, T. laevis, T. planctonicus) and three non-typical varieties (T. brebissonii var. minor, T. laevis var. borgei, T. laevis var. minutus).

Marine algae are central to global carbon fixation, and their productivity is dictated largely by resource availability. Reduced nutrient availability is predicted for vast oceanic regions as an outcome of climate change; however, there is much to learn regarding response mechanisms of the tiny picoplankton that thrive in these environments, especially eukaryotic phytoplankton. Here, we investigate responses of the picoeukaryote Micromonas commoda, a green alga found throughout subtropical and tropical oceans. Under shifting phosphate availability scenarios, transcriptomic analyses revealed altered expression of transfer RNA modification enzymes and biased codon usage of transcripts more abundant during phosphate-limiting versus phosphate-replete conditions, consistent with the role of transfer RNA modifications in regulating codon recognition. To associate the observed shift in the expression of the transfer RNA modification enzyme complement with the transfer RNAs encoded by M. commoda, we also determined the transfer RNA repertoire of this alga revealing potential targets of the modification enzymes. Codon usage bias was particularly pronounced in transcripts encoding proteins with direct roles in managing phosphate limitation and photosystem-associated proteins that have ill-characterized putative functions in "light stress." The observed codon usage bias corresponds to a proposed stress response mechanism in which the interplay between stress-induced changes in transfer RNA modifications and skewed codon usage in certain essential response genes drives preferential translation of the encoded proteins. Collectively, we expose a potential underlying mechanism for achieving growth under enhanced nutrient limitation that extends beyond the catalog of up- or downregulated protein-encoding genes to the cell biological controls that underpin acclimation to changing environmental conditions., (© The Author(s) 2023. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

The Klebsormidiophyceae are a class of green microalgae observed globally in both freshwater and terrestrial habitats. Morphology-based classification schemes of this class have been shown to be inadequate due to the simple morphology of these algae, the tendency of morphology to vary in culture versus field conditions, and rampant morphological homoplasy. Molecular studies revealing cryptic diversity have renewed interest in this group. We sequenced the complete chloroplast genomes of a broad series of taxa spanning the known taxonomic breadth of this class. We also sequenced the chloroplast genomes of three strains of Streptofilum, a recently discovered green algal lineage with close affinity to the Klebsormidiophyceae. Our results affirm the previously hypothesized polyphyly of the genus Klebsormidium as well as the polyphyly of the nominal species in this genus, K. flaccidum. Furthermore, plastome sequences strongly support the status of Streptofilum as a distinct, early-diverging lineage of charophytic algae sister to a clade comprising Klebsormidiophyceae plus Phragmoplastophyta. We also uncovered major structural alterations in the chloroplast genomes of species in Klebsormidium that have broad implications regarding the underlying mechanisms of chloroplast genome evolution., (© 2023 The Authors. Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Phytoplankton are exposed to dramatic variations in light quality when cells are carried by upwelling or downwelling currents or encounter sediment. We investigated the potential impact of light quality changes in Ostreococcus, a key marine photosynthetic picoeukaryote, by analysing changes in its transcriptome, pigment content, and photophysiology after acclimation to monochromatic red, green, or blue light. The clade B species RCC809, isolated from the deep euphotic zone of the tropical Atlantic Ocean, responded to blue light by accelerating cell division at the expense of storage reserves and by increasing the relative level of blue-light-absorbing pigments. It responded to red and green light by increasing its potential for photoprotection. In contrast, the clade A species OTTH0595, which originated from a shallow water environment, showed no difference in photosynthetic properties and minor differences in carotenoid contents between light qualities. This was associated with the loss of candidate light-quality responsive promoter motifs identified in RCC809 genes. These results demonstrate that light quality can have a major influence on the physiology of eukaryotic phytoplankton and suggest that different light quality environments can drive selection for diverse patterns of responsiveness and environmental niche partitioning., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Oral administration of rhamnan sulfate (RS), derived from the seaweed Monostroma nitidum , markedly suppresses inflammatory damage in the vascular endothelium and organs of lipopolysaccharide-treated mice. This study aimed to analyze whether orally administered RS inhibits the development of atherosclerosis, a chronic inflammation of the arteries. ApoE-deficient female mice were fed a normal or high-fat diet (HFD) with or without RS for 12 weeks. Immunohistochemical and mRNA analyses of atherosclerosis-related genes were performed. The effect of RS on the migration of RAW264.7 cells was also examined in vitro. RS administration suppressed the increase in blood total cholesterol and triglyceride levels. In the aorta of HFD-fed mice, RS reduced vascular smooth muscle cell proliferation, macrophage accumulation, and elevation of VCAM-1 and inhibited the reduction of Robo4. Increased mRNA levels of Vcam1 , Mmp9 , and Srebp1 in atherosclerotic areas of HFD-fed mice were also suppressed with RS. Moreover, RS directly inhibited the migration of RAW264.7 cells in vitro. Thus, in HFD-fed ApoE-deficient mice, oral administration of RS ameliorated abnormal lipid metabolism and reduced vascular endothelial inflammation and hyperpermeability, macrophage infiltration and accumulation, and smooth muscle cell proliferation in the arteries leading to atherosclerosis. These results suggest that RS is an effective functional food for the prevention of atherosclerosis.

Melting snow and glacier surfaces host microalgal blooms in polar and mountainous regions. The aim of this study was to determine the dominant taxa at the species level in the European Arctic and the Alps. A standardized protocol for amplicon metabarcoding using the 18S rRNA gene and ITS2 markers was developed. This is important because previous biodiversity studies have been hampered by the dominance of closely related algal taxa in snow and ice. Due to the limited resolution of partial 18S rRNA Illumina sequences, the hypervariable ITS2 region was used to further discriminate between the genotypes. Our results show that red snow was caused by the cosmopolitan Sanguina nivaloides (Chlamydomonadales, Chlorophyta) and two as of yet undescribed Sanguina species. Arctic orange snow was dominated by S. aurantia, which was not found in the Alps. On glaciers, at least three Ancylonema species (Zygnematales, Streptophyta) dominated. Golden-brown blooms consisted of Hydrurus spp. (Hydrurales, Stramenophiles) and these were mainly an Arctic phenomenon. For chrysophytes, only the 18S rRNA gene but not ITS2 sequences were amplified, showcasing how delicate the selection of eukaryotic 'universal' primers for community studies is and that primer specificity will affect diversity results dramatically. We propose our approach as a 'best practice'., (© The Author(s) 2023. Published by Oxford University Press on behalf of FEMS.)

NO is a gaseous signaling redox-active molecule that functions in various eukaryotes. However, its synthesis, turnover, and effects in cells are specific in plants in several aspects. Compared with higher plants, the role of NO in Chlorophyta has not been investigated enough. However, some of the mechanisms for controlling the levels of this signaling molecule have been characterized in model green algae. In Chlamydomonas reinhardtii, NO synthesis is carried out by a dual system of nitrate reductase and NO-forming nitrite reductase. Other mechanisms that might produce NO from nitrite are associated with components of the mitochondrial electron-transport chain. In addition, NO formation in some green algae proceeds by an oxidative mechanism similar to that in mammals. The recent discovery of L-arginine-dependent NO synthesis in the colorless alga Polytomella parva suggests the existence of a protein complex with enzyme activities that are similar to animal nitric oxide synthase. This latter finding paves the way for further research into potential members of the NO synthases family in Chlorophyta. Beyond synthesis, the regulatory processes to maintain intracellular NO levels are also an integral part for its function in cells. Members of the truncated hemoglobins family with dioxygenase activity can convert NO to nitrate, as was shown for C. reinhardtii. In addition, the implication of NO reductases in NO scavenging has also been described. Even more intriguing, unlike in animals, the typical NO/cGMP signaling module appears not to be used by green algae. S-nitrosylated glutathione, which is considered the main reservoir for NO, provides NO signals to proteins. In Chlorophyta, protein S-nitrosation is one of the key mechanisms of action of the redox molecule. In this review, we discuss the current state-of-the-art and possible future directions related to the biology of NO in green algae.