The green algae CO concentrating mechanism and photorespiration jointly operate during acclimation to low CO.

Due to low availability of CO in aquatic environment, microalgae have evolved a CO concentrating mechanism (CCM). It has long been thought that operation of CCM would suppress photorespiration by increasing the CO concentration at the Rubisco active site, but experimental evidence is scarce. To better explore the function of photorespiration in algae, we first characterized a Chlamydomonas reinhardtii mutant defected in low-CO inducible 20 (LCI20) and show that LCI20 is a chloroplast-envelope glutamate/malate transporter playing a role in photorespiration.

The cell biology and genome of , a giant cell that embeds symbiotic algae in a microtubule meshwork.

Endosymbiotic events in which an endosymbiont is retained within a cell that remains capable of phagocytosis, a situation known as mixotrophy, provide potentially important clues about the eukaryotic evolution. Here we describe the cell biology and genome of the giant mixotrophic ciliate . We show that contains as an endosymbiont that retains the ability to live outside the host.

Dramatic changes in mitochondrial subcellular location and morphology accompany activation of the CO concentrating mechanism.

Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for ~50% of global photosynthesis, compartmentalize their Ribulose 1,5 Bisphosphate Carboxylase/Oxygenase (Rubisco) into a specialized structure known as the pyrenoid when the cells experience limiting CO conditions; this compartmentalization is a component of the CO Concentrating Mechanism (CCM), which facilitates photosynthetic CO fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO limitation, although a role for this reorganization in CCM function remains unclear.

Absence of alka(e)nes triggers profound remodeling of glycerolipid and carotenoid composition in cyanobacteria membrane.

Alka(e)nes are produced by many living organisms and exhibit diverse physiological roles, reflecting a high functional versatility. Alka(e)nes serve as waterproof wax in plants, communicating pheromones for insects, and microbial signaling molecules in some bacteria. Although alka(e)nes have been found in cyanobacteria and algal chloroplasts, their importance for photosynthetic membranes has remained elusive.

Coordinated wound responses in a regenerative animal-algal holobiont.

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.

Alternative electron pathways of photosynthesis power green algal CO2 capture.

Microalgae contribute to about half of global net photosynthesis, which converts sunlight into the chemical energy (ATP and NADPH) used to transform CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required to sustain CO2 fixation. However, the relative importance of each alternative pathway remains elusive.

Dramatic Changes in Mitochondrial Subcellular Location and Morphology Accompany Activation of the CO Concentrating Mechanism.

Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for ~50% of global photosynthesis, compartmentalize their Rubisco into a specialized structure known as the pyrenoid when the cells experience limiting CO conditions; this compartmentalization appears to be a component of the CO Concentrating Mechanism (CCM), which facilitates photosynthetic CO fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO limiting conditions, although a role for this reorganization in CCM function remains unclear.

Crosstalk between photosynthesis and respiration in microbes.

Phototrophic organisms harbor two main bioenergetic hubs, photosynthesis and respiration, and these processes dynamically exchange and share metabolites to balance the energy of the cell. In microalgae and cyanobacteria, the crosstalk between the light-triggered reactions of photosynthesis and respiration is particularly prominent with respiratory O uptake which can be stimulated upon illumination. Since its discovery, this light-enhanced respiration has been proposed to be critical in dissipating the excess reducing power generated by photosynthesis.

The role of BST4 in the pyrenoid of .

In many eukaryotic algae, CO fixation by Rubisco is enhanced by a CO-concentrating mechanism, which utilizes a Rubisco-rich organelle called the pyrenoid. The pyrenoid is traversed by a network of thylakoid-membranes called pyrenoid tubules, proposed to deliver CO. In the model alga (), the pyrenoid tubules have been proposed to be tethered to the Rubisco matrix by a bestrophin-like transmembrane protein, BST4.

Quantifying the roles of algal photosynthetic electron pathways: a milestone towards photosynthetic robustness.

During photosynthesis, electron transport reactions generate and shuttle reductant to allow CO reduction by the Calvin-Benson-Bassham cycle and the formation of biomass building block in the so-called linear electron flow (LEF). However, in nature, environmental parameters like light intensity or CO availability can vary and quickly change photosynthesis rates, creating an imbalance between photosynthetic energy production and metabolic needs. In addition to LEF, alternative photosynthetic electron flows are central to allow photosynthetic energy to match metabolic demand in response to environmental variations.

Energy crosstalk between photosynthesis and the algal CO-concentrating mechanisms.

Microalgal photosynthesis is responsible for nearly half of the CO annually captured by Earth's ecosystems. In aquatic environments where the CO availability is low, the CO-fixing efficiency of microalgae greatly relies on mechanisms - called COconcentrating mechanisms (CCMs) - for concentrating CO at the catalytic site of the CO-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). While the transport of inorganic carbon (C) across membrane bilayers against a concentration gradient consumes part of the chemical energy generated by photosynthesis, the bioenergetics and cellular mechanisms involved are only beginning to be elucidated.

Interplay between LHCSR proteins and state transitions governs the NPQ response in Chlamydomonas during light fluctuations.

Photosynthetic organisms use sunlight as the primary energy source to fix CO . However, in nature, light energy is highly variable, reaching levels of saturation for periods ranging from milliseconds to hours. In the green microalga Chlamydomonas reinhardtii, safe dissipation of excess light energy by nonphotochemical quenching (NPQ) is mediated by light-harvesting complex stress-related (LHCSR) proteins and redistribution of light-harvesting antennae between the photosystems (state transition).

Alternative photosynthesis pathways drive the algal CO-concentrating mechanism.

Global photosynthesis consumes ten times more CO than net anthropogenic emissions, and microalgae account for nearly half of this consumption. The high efficiency of algal photosynthesis relies on a mechanism concentrating CO (CCM) at the catalytic site of the carboxylating enzyme RuBisCO, which enhances CO fixation. Although many cellular components involved in the transport and sequestration of inorganic carbon have been identified, how microalgae supply energy to concentrate CO against a thermodynamic gradient remains unknown.

Coral symbionts evolved a functional polycistronic flavodiiron gene.

Photosynthesis in cyanobacteria, green algae, and basal land plants is protected against excess reducing pressure on the photosynthetic chain by flavodiiron proteins (FLV) that dissipate photosynthetic electrons by reducing O. In these organisms, the genes encoding FLV are always conserved in the form of a pair of two-type isozymes (FLVA and FLVB) that are believed to function in O photo-reduction as a heterodimer. While coral symbionts (dinoflagellates of the family Symbiodiniaceae) are the only algae to harbor FLV in photosynthetic red plastid lineage, only one gene is found in transcriptomes and its role and activity remain unknown.

Fatty acid photodecarboxylase is an ancient photoenzyme that forms hydrocarbons in the thylakoids of algae.

Fatty acid photodecarboxylase (FAP) is one of the few enzymes that require light for their catalytic cycle (photoenzymes). FAP was first identified in the microalga Chlorella variabilis NC64A, and belongs to an algae-specific subgroup of the glucose-methanol-choline oxidoreductase family. While the FAP from C.

Role of an ancient light-harvesting protein of PSI in light absorption and photoprotection.

Diverse algae of the red lineage possess chlorophyll a-binding proteins termed LHCR, comprising the PSI light-harvesting system, which represent an ancient antenna form that evolved in red algae and was acquired through secondary endosymbiosis. However, the function and regulation of LHCR complexes remain obscure. Here we describe isolation of a Nannochloropsis oceanica LHCR mutant, named hlr1, which exhibits a greater tolerance to high-light (HL) stress compared to the wild type.

Corrigendum: Membrane Inlet Mass Spectrometry: A Powerful Tool for Algal Research.

[This corrects the article DOI: 10.3389/fpls.2020.

Membrane Inlet Mass Spectrometry: A Powerful Tool for Algal Research.

Since the first great oxygenation event, photosynthetic microorganisms have continuously shaped the Earth's atmosphere. Studying biological mechanisms involved in the interaction between microalgae and cyanobacteria with the Earth's atmosphere requires the monitoring of gas exchange. Membrane inlet mass spectrometry (MIMS) has been developed in the early 1960s to study gas exchange mechanisms of photosynthetic cells.

Membrane Inlet Mass Spectrometry at the Crossroads of Photosynthesis, Biofuel, and Climate Research.

Advances in algal biology have built on gas exchange measurements by MIMS in the fields of photosynthesis, biofuel production, and climate research.

Subcellular Energetics and Carbon Storage in .

Microalgae have emerged as a promising platform for production of carbon- and energy- rich molecules, notably starch and oil. Establishing an economically viable algal biotechnology sector requires a holistic understanding of algal photosynthesis, physiology, cell cycle and metabolism. Starch/oil productivity is a combined effect of their cellular content and cell division activities.

Continuous photoproduction of hydrocarbon drop-in fuel by microbial cell factories.

Use of microbes to produce liquid transportation fuels is not yet economically viable. A key point to reduce production costs is the design a cell factory that combines the continuous production of drop-in fuel molecules with the ability to recover products from the cell culture at low cost. Medium-chain hydrocarbons seem ideal targets because they can be produced from abundant fatty acids and, due to their volatility, can be easily collected in gas phase.