An unexpected hydratase synthesizes the green light-absorbing pigment fucoxanthin

Decreasing protein biotinylation background in a diatom facilitates proximity labeling of the periplastidial compartment proteome

Diatoms are ecologically and industrially significant microalgae, crucial for global carbon fixation and biotechnological applications. Their complex plastid membrane structures, resulting from secondary endosymbiosis, remain poorly characterized, particularly the periplastidial compartment (PPC). Proximity labeling techniques, such as TurboID and ascorbate peroxidase 2 (APEX2)-based labeling, are powerful tools for identifying protein-protein interactions and spatial proteomes, but their application in diatoms is hindered by unknown factors. In this study, we identified and characterized the high biotinylation background in diatoms, including Phaeodactylum tricornutum and other microalgae, which significantly impairs the effectiveness of proximity labeling. We also characterized the biotin synthase (BIOB) in P. tricornutum, a key enzyme in biotin biosynthesis. By using a biob mutant to deplete biotin, we successfully decreased the biotinylation background, enhancing the sensitivity and quality of proximity labeling. Applying this approach to the PPC, we identified several proteins previously undetectable through bioinformatics and confocal microscopy. Our results demonstrate that inhibiting biotin synthesis improves TurboID-based proximity labeling methods for studying protein interactions and spatial proteomics in diatoms. The case study of the improved proximity labeling system in PPC also increased our understanding of the complex plastids derived from higher-order endosymbiosis.

Metabolic engineering and cultivation strategies for efficient production of fucoxanthin and related carotenoids

Fucoxanthin, a bioactive carotenoid derived from algae, has attracted considerable attention for its applications in health, cosmetics, and nutrition. Advances in metabolic engineering, such as the overexpression of pathway-specific enzymes and enhancement of precursor availability, have shown promising results in improving production efficiency. However, despite its high value, the biosynthetic pathway of fucoxanthin remains only partially elucidated, posing significant challenges for metabolic engineering efforts. Recent studies have identified previously unknown enzymes and regulatory elements within the pathway, providing opportunities for further productivity enhancements through targeted metabolic modifications. Additionally, adaptive evolution, mutagenesis-driven strain development, and optimized cultivation conditions have demonstrated significant potential to boost fucoxanthin yields. This review consolidates the latest insights into the biosynthetic pathway of fucoxanthin and highlights metabolic engineering strategies aimed at enhancing the production of fucoxanthin and related carotenoids, offering approaches to design high-yielding strains. Furthermore, recent advancements in random mutagenesis and cultivation technology are discussed. By integrating these developments, more economically viable and environmentally sustainable fucoxanthin production systems can be achieved. KEY POINTS : • Insights into fucoxanthin biosynthesis enable targeted metabolic engineering. • ALE and cultivation strategies complement metabolic engineering efforts. • Balanced push-pull-block strategies improve fucoxanthin production efficiency.

The heat and irradiation driven degradation of the diagnostic pigments in marine phytoplankton and the compositions of special degradation products

Marine phytoplankton stands as one of the most crucial components of marine ecosystems, so tracking it using appropriate biomarkers holds significant meaning. Chlorins are a sort of degradation products derived from the diagnostic pigment of marine phytoplankton and serve as valuable biomarkers for describing the temporal and spatial distribution of phytoplankton. However, previous research has not qualitatively or quantitatively studied multiple Chlorins, nor has it clearly revealed the conditions of their formation. Thus, this study investigated the chemical structure and formation mechanism of Chlorins in Chlorophytes, Prochlorococcus, and Chrysophytes communities by experiencing specific heat and irradiation conditions. According to the standardized redundancy analysis results, Phytin-a and its analogues with shorter phytyl chain are sensitive to irradiation intensity, and different Phytin-a analogues represent different degradation pathway of Chl-a. The composition and concentration of Phide-a and its further degradation products emerged as the primary thermosensitive components, capable of indicating and reversing temperature fluctuations within the environment. During the degradation processes of Chl-a, the carotenoids of each phytoplankton can also affect the degradation direction of Chl-a. Phycourobilin can cause Chl-a in the Prochlorococcus group to transform into special Phide-a analogues relying on low irradiation intensity. Zeaxanthin and Diatoxanthin dominate the conversion of Chl-a in Chrysophytes, and tend to cause heat-driven degradation of pigments. Zeaxanthin and Prasinoxanthin can also mediate the degradation of Chl-a in Chlorophytes. Thus, Chlorophyll and the composition of its Chlorins briefly reveal the rates of degradation and light intensity, and the carotenoids and their Chlorins can represent the temperature condition in the environment. These results imply that Chlorins can be utilized as biomarkers to infer the distribution and abundance of phytoplankton communities, reflecting the environmental factors in which phytoplankton live.

Distribution, Biosynthesis, and Function of Carotenoids in Oxygenic Phototrophic Algae

For photosynthesis, oxygenic phototrophic organisms necessarily contain not only chlorophylls but also carotenoids. Various carotenoids have been identified in algae and taxonomic studies of algae have been conducted. In this review, the relationship between the distribution of chlorophylls and carotenoids and the phylogeny of sea and freshwater oxygenic phototrophs, including cyanobacteria, red algae, brown algae, and green algae, is summarized. These phototrophs contain division- or class-specific chlorophylls and carotenoids, such as fucoxanthin, peridinin, diadinoxanthin, and siphonaxanthin. The distribution of β-carotene and its derivatives, including β-carotene, zeaxanthin, violaxanthin, neoxanthin, diadinoxanthin, fucoxanthin, and peridinin (β-branch carotenoids), are limited to divisions of a part of Rhodophyta, Cryptophyta, Heterokontophyta, Haptophyta, and Dinophyta. Meanwhile, the distribution of α-carotene and its derivatives, such as lutein, loroxanthin, and siphonaxanthin (α-branch carotenoids), are limited to divisions of a part of Rhodophyta (macrophytic type), Cryptophyta, Euglenophyta, Chlorarachniophyta, and Chlorophyta. In addition, carotenogenesis pathways are also discussed based on the chemical structures of carotenoids and the known characteristics of carotenogenesis enzymes in other organisms. The specific genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction centers and light-harvesting complexes. Some carotenoids function in photosynthesis and are briefly summarized. Water-soluble peridinin-chlorophyll a-protein (PCP) and orange carotenoid protein (OCP) have also been characterized. This review is a summary and update from the previous review on the distribution of major carotenoids, primary carotenogenesis pathways, and the characteristics of carotenogenesis enzymes and genes.

Identifying the gene responsible for non-photochemical quenching reversal in Phaeodactylum tricornutum

Algae such as diatoms and haptophytes have distinct photosynthetic pigments from plants, including a novel set of carotenoids. This includes a primary xanthophyll cycle comprised of diadinoxanthin and its de-epoxidation product diatoxanthin that enables the switch between light harvesting and non-photochemical quenching (NPQ)-mediated dissipation of light energy. The enzyme responsible for the reversal of this cycle was previously unknown. Here, we identified zeaxanthin epoxidase 3 (ZEP3) from Phaeodactylum tricornutum as the candidate diatoxanthin epoxidase. Knocking out the ZEP3 gene caused a loss of rapidly reversible NPQ following saturating light exposure. This correlated with the maintenance of high concentrations of diatoxanthin during recovery in low light. Xanthophyll cycling and NPQ relaxation were restored via complementation of the wild-type ZEP3 gene. The zep3 knockout strains showed reduced photosynthetic rates at higher light fluxes and reduced specific growth rate in variable light regimes, likely due to the mutant strains becoming locked in a light energy dissipation state. We were able to toggle the level of NPQ capacity in a time and dose dependent manner by placing the ZEP3 gene under the control of a β-estradiol inducible promoter. Identification of this gene provides a deeper understanding of the diversification of photosynthetic control in algae compared to plants and suggests a potential target to improve the productivity of industrial-scale cultures.

Unlocking the Green Gold: Exploring the Cancer Treatment and the Other Therapeutic Potential of Fucoxanthin Derivatives from Microalgae

Fucoxanthin, a carotenoid widely studied in marine microalgae, is at the heart of scientific research because of its promising bioactive properties for human health. Its unique chemical structure and specific biosynthesis, characterized by complex enzymatic conversion in marine organisms, have been examined in depth in this review. The antioxidant, anti-inflammatory, and anti-cancer activities of fucoxanthin have been rigorously supported by data from in vitro and in vivo experiments and early clinical trials. Additionally, this review explores emerging strategies to optimize the stability and efficacy of fucoxanthin, aiming to increase its solubility and bioavailability to enhance its therapeutic applications. However, despite these potential benefits, challenges persist, such as limited bioavailability and technological obstacles hindering its large-scale production. The medical exploitation of fucoxanthin thus requires an innovative approach and continuous optimization to overcome these barriers. Although further research is needed to refine its clinical use, fucoxanthin offers promising potential in the development of natural therapies aimed at improving human health. By integrating knowledge about its biosynthesis, mechanisms of action, and potential beneficial effects, future studies could open new perspectives in the treatment of cancer and other chronic diseases.

The role of cis-zeatin in enhancing high-temperature resistance and fucoxanthin biosynthesis in Phaeodactylum tricornutum

Phaeodactylum tricornutum a prominent source of industrial fucoxanthin production, faces challenges in its application due to its tolerance to high-temperature environments. This study investigates the physiological responses of P. tricornutum to high-temperature stress and its impact on fucoxanthin content, with a specific focus on the role of cis-zeatin. The results reveal that high-temperature stress inhibits P. tricornutum's growth and photosynthetic activity, leading to a decrease in fucoxanthin content. Transcriptome analysis shows that high temperature suppresses the expression of genes related to photosynthesis (e.g., psbO, psbQ, and OEC) and fucoxanthin biosynthesis (e.g., PYS, PDS1, and PSD2), underscoring the negative effects of high temperature on P. tricornutum. Interestingly, genes associated with cis-zeatin biosynthesis and cytokinesis signaling pathways exhibited increased expression under high-temperature conditions, indicating a potential role of cis-zeatin signaling in response to elevated temperatures. Content measurements confirm that high temperature enhances cis-zeatin content. Furthermore, the exogenous addition of cytokinesis mimetics or inhibitors significantly affected P. tricornutum's high-temperature resistance. Overexpression of the cis-zeatin biosynthetic enzyme gene tRNA DMATase enhanced P. tricornutum's resistance to high-temperature stress, while genetic knockout of tRNA DMATase reduced its resistance to high temperatures. Therefore, this research not only uncovers a novel mechanism for high-temperature resistance in P. tricornutum but also offers a possible alga species that can withstand high temperatures for the industrial production of fucoxanthin, offering valuable insights for practical utilization.IMPORTANCEThis study delves into Phaeodactylum tricornutum's response to high-temperature stress, specifically focusing on cis-zeatin. We uncover inhibited growth, reduced fucoxanthin, and significant cis-zeatin-related gene expression under high temperatures, highlighting potential signaling mechanisms. Crucially, genetic engineering and exogenous addition experiments confirm that the change in cis-zeatin levels could influence P. tricornutum's resistance to high-temperature stress. This breakthrough deepens our understanding of microalgae adaptation to high temperatures and offers an innovative angle for industrial fucoxanthin production. This research is a pivotal step toward developing heat-resistant microalgae for industrial use.

Molecular design of microalgae as sustainable cell factories

Microalgae are regarded as sustainable and potent chassis for biotechnology. Their capacity for efficient photosynthesis fuels dynamic growth independent from organic carbon sources and converts atmospheric CO2 directly into various valuable hydrocarbon-based metabolites. However, approaches to gene expression and metabolic regulation have been inferior to those in more established heterotrophs (e.g., prokaryotes or yeast) since the genetic tools and insights in expression regulation have been distinctly less advanced. In recent years, however, these tools and their efficiency have dramatically improved. Various examples have demonstrated new trends in microalgal biotechnology and the potential of microalgae for the transition towards a sustainable bioeconomy.

Zeaxanthin epoxidase 3 Knockout Mutants of the Model Diatom Phaeodactylum tricornutum Enable Commercial Production of the Bioactive Carotenoid Diatoxanthin

Carotenoids are pigments that have a range of functions in human health. The carotenoid diatoxanthin is suggested to have antioxidant, anti-inflammatory and chemo-preventive properties. Diatoxanthin is only produced by a few groups of microalgae, where it functions in photoprotection. Its large-scale production in microalgae is currently not feasible. In fact, rapid conversion into the inactive pigment diadinoxanthin is triggered when cells are removed from a high-intensity light source, which is the case during large-scale harvesting of microalgae biomass. Zeaxanthin epoxidase (ZEP) 2 and/or ZEP3 have been suggested to be responsible for the back-conversion of high-light accumulated diatoxanthin to diadinoxanthin in low-light in diatoms. Using CRISPR/Cas9 gene editing technology, we knocked out the ZEP2 and ZEP3 genes in the marine diatom Phaeodactylum tricornutum to investigate their role in the diadinoxanthin-diatoxanthin cycle and determine if one of the mutant strains could function as a diatoxanthin production line. Light-shift experiments proved that ZEP3 encodes the enzyme converting diatoxanthin to diadinoxanthin in low light. Loss of ZEP3 caused the high-light-accumulated diatoxanthin to be stable for several hours after the cultures had been returned to low light, suggesting that zep3 mutant strains could be suitable as commercial production lines of diatoxanthin.

A key gene, violaxanthin de-epoxidase-like 1, enhances fucoxanthin accumulation in Phaeodactylum tricornutum

BACKGROUND

Fucoxanthin has been widely investigated owing to its beneficial biological properties, and the model diatom Phaeodactylum tricornutum, possessing fucoxanthin (Fux) chlorophyll proteins as light-harvesting systems, is considered to have the potential to become a commercial cell factory for the pigment production.

RESULTS

Here, we compared the pigment contents in 10 different P. tricornutum strains from the globe, and found that strain CCMP631 (Pt6) exhibited the highest Fux content but with a low biomass. Comparison of mRNA levels revealed that higher Fux content in Pt6 was related with the higher expression of gene violaxanthin de-epoxidase-like (VDL) protein 1 (VDL1), which encodes the enzyme catalyzing the tautomerization of violaxanthin to neoxanthin in Fux biosynthesis pathway. Single nucleotide variants of VDL1 gene and allele-specific expression in strains Pt1 (the whole genome sequenced strain CCMP632) and Pt6 were analyzed, and overexpressing of each of the 4 VDL1 alleles, two from Pt1 and two from Pt6, in strain Pt1 leads to an increase in downstream product diadinoxanthin and channels the pigments towards Fux biosynthesis. All the 8 VDL1 overexpression (OE) lines showed significant increases by 8.2 to 41.7% in Fux content without compromising growth, and VDL1 Allele 2 OE lines even exhibited the higher cell density on day 8, with an increase by 24.2-28.7% in two Pt1VDL1-allele 2 OE lines and 7.1-11.1% in two Pt6VDL1-allele 2 OE lines, respectively.

CONCLUSIONS

The results reveal VDL1, localized in the plastid stroma, plays a key role in Fux over-accumulation in P. tricornutum. Overexpressing VDL1, especially allele 2, improved both the Fux content and growth rate, which provides a new strategy for the manipulation of Fux production in the future.

Biosynthesis of chlorophyll c in a dinoflagellate and heterologous production in planta

Chlorophyll c is a key photosynthetic pigment that has been used historically to classify eukaryotic algae. Despite its importance in global photosynthetic productivity, the pathway for its biosynthesis has remained elusive. Here we define the CHLOROPHYLL C SYNTHASE (CHLCS) discovered through investigation of a dinoflagellate mutant deficient in chlorophyll c. CHLCSs are proteins with chlorophyll a/b binding and 2-oxoglutarate-Fe(II) dioxygenase (2OGD) domains found in peridinin-containing dinoflagellates; other chlorophyll c-containing algae utilize enzymes with only the 2OGD domain or an unknown synthase to produce chlorophyll c. 2OGD-containing synthases across dinoflagellate, diatom, cryptophyte, and haptophyte lineages form a monophyletic group, 8 members of which were also shown to produce chlorophyll c. Chlorophyll c1 to c2 ratios in marine algae are dictated in part by chlorophyll c synthases. CHLCS heterologously expressed in planta results in the accumulation of chlorophyll c1 and c2, demonstrating a path to augment plant pigment composition with algal counterparts.

Mediator subunit MED8 interacts with heat shock transcription factor HSF3 to promote fucoxanthin synthesis in the diatom Phaeodactylum tricornutum

Fucoxanthin, a natural carotenoid that has substantial pharmaceutical value due to its anticancer, antioxidant, antiobesity, and antidiabetic properties, is biosynthesized from glyceraldehyde-3-phosphate (G3P) via a series of enzymatic reactions. However, our understanding of the transcriptional mechanisms involved in fucoxanthin biosynthesis remains limited. Using reverse genetics, the med8 mutant was identified based on its phenotype of reduced fucoxanthin content, and the biological functions of MED8 in fucoxanthin synthesis were characterized using approaches such as gene expression, protein subcellular localization, protein-protein interaction and chromatin immunoprecipitation assay. Gene-editing mutants of MED8 exhibited decreased fucoxanthin content as well as reduced expression levels of six key genes involved in fucoxanthin synthesis, namely DXS, PSY1, ZDS-like, CRTISO5, ZEP1, and ZEP3, when compared to the wild-type (WT) strain. Furthermore, we showed that MED8 interacts with HSF3, and genetic analysis revealed their shared involvement in the genetic pathway governing fucoxanthin synthesis. Additionally, HSF3 was required for MED8 association with the promoters of the six fucoxanthin synthesis genes. In conclusion, MED8 and HSF3 are involved in fucoxanthin synthesis by modulating the expression of the fucoxanthin synthesis genes. Our results increase the understanding of the molecular regulation mechanisms underlying fucoxanthin synthesis in the diatom P. tricornutum.

Synthetic biology in microalgae towards fucoxanthin production for pharmacy and nutraceuticals

Synthetic biology has emerged as a powerful tool for engineering biological systems to produce valuable compounds, including pharmaceuticals and nutraceuticals. Microalgae, in particular, offer a promising platform for the production of bioactive compounds due to their high productivity, low land and water requirements, and ability to perform photosynthesis. Fucoxanthin, a carotenoid pigment found predominantly in brown seaweeds and certain microalgae, has gained significant attention in recent years due to its numerous health benefits, such as antioxidation, antitumor effect and precaution osteoporosis. This review provides an overview of the principles and applications of synthetic biology in the microbial engineering of microalgae for enhanced fucoxanthin production. Firstly, the fucoxanthin bioavailability and metabolism in vivo was introduced for the beneficial roles, followed by the biological functions of anti-oxidant activity, anti-inflammatory activity, antiapoptotic role antidiabetic and antilipemic effects. Secondly, the cultivation condition and strategy were summarized for fucoxanthin improvement with low production costs. Thirdly, the genetic engineering of microalgae, including gene overexpression, knockdown and knockout strategies were discussed for further improving the fucoxanthin production. Then, synthetic biology tools of CRISPR-Cas9 genome editing, transcription activator-like effector nucleases as well as modular assembly and chassis engineering were proposed to precise modification of microalgal genomes to improve fucoxanthin production. Finally, challenges and future perspectives were discussed to realize the industrial production and development of functional foods of fucoxanthin from microalgae.

Overexpression of PtVDL1 in Phaeodactylum tricornutum Increases Fucoxanthin Content under Red Light

Phaeodactylum tricornutum is a model diatom with significant biotechnological applications, including enhancing biomass, biofuel, and carotenoid production. Specifically, owing to the capacity of this organism to serve as a valuable source of essential raw materials for pharmaceuticals and nutraceuticals, ongoing research is actively focused on enhancing its productivity. One of the genes involved in various stages of fucoxanthin (Fx) biosynthesis, violaxanthin de-epoxidase like 1 (VDL1), has recently been identified. To validate the intracellular function of this gene and boost Fx production through overexpression, we established and examined three transgenic P. tricornutum lines characterized by elevated P. tricortunum VDL1 ( PtVDL1) expression and evaluate their cell growth and Fx productivity. These transgenic lines exhibited substantially increased PtVDL1 mRNA and protein levels compared to the wild type (WT). Notably, the enzyme substrate violaxanthin was entirely depleted and could not be detected in the transformants, whereas it remained at constant levels in the WT. Interestingly, under standard white light conditions, Fx productivity in the transformants remained unchanged; however, but after 48 h of exposure to red light, it increased by up to 15%. These results indicate that PtVDL1-overexpressing P. tricornutum has industrial potential, particularly for enhancing Fx production under red light conditions.