Biology subjects

Peltier, G.

Publications and source records attributed to Peltier, G..

12 recordsLinked to original sources

bioRxiv2024

Joint operation of the CO2 concentrating mechanism and photorespiration in green algae during acclimation to limiting CO2

Due to low availability of CO2 in aquatic environment, microalgae have evolved a CO2 concentrating mechanism (CCM). It has long been thought that operation of CCM would suppress photorespiration by increasing the CO2 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-CO2 inducible 20 (LCI20) and show that LCI20 is a chloroplast-envelope glutamate/malate transporter playing a role in photorespiration. By monitoring growth and glycolate excretion in mutants deficient in either CCM or photorespiration, we conclude that: i. CCM induction does not depend on photorespiration, ii. glycolate excretion protects algal cells from the toxicity of unmetabolized photorespiratory intermediates, iii. photorespiration is active at low CO2 when the CCM is operational. This work provides a foundation for a better understanding of the carbon cycle in the ocean where significant glycolate concentrations have been found.

plant biology↗

bioRxiv2024

DYRKP kinase regulates cell wall degradation in Chlamydomonas by inducing matrix metalloproteinase expression

The cell wall of plants and algae is an important cell structure that protects cells from changes in the external physical and chemical environment. This extracellular matrix composed of polysaccharides and glycoproteins, is needed to be remodeled continuously throughout the life cycle. However, compared to matrix polysaccharides, little is known about the mechanisms regulating the formation and degradation of matrix glycoproteins. We report here that a plant kinase belonging to the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family present in all eukaryotes regulates cell wall degradation in the model microalga Chlamydomonas reinhardtii by inducing the expression of matrix metalloproteinases (MMPs). In the absence of DYRKP, daughter cells fail to degrade the parental cell wall, and form multicellular structures. On the other hand, the complementation line of DYRKP was shown to degrade the parental cell wall normally. Transcriptomic and proteomic analyses indicate a marked down-regulation of MMP expression in the dyrkp mutants. Additionally, the expression of MMP was confirmed to be consistent with the expression pattern of DYRKP. Our findings show that DYRKP, by ensuring timely MMP expression, enables the successful execution of the cell cycle. Altogether, this study provides new insight into the life cycle regulation in plants and algae. IN A NUTSHELLO_ST_ABSBackgroundC_ST_ABSPlants and algae have different types of polysaccharides in their cell walls, but they have glycoproteins in common. Glycoprotein synthesis and degradation must be tightly regulated to ensure normal growth and differentiation. However, little is known about the regulatory mechanism of glycoprotein degradation in both plants and algae. The cell cycle of Chlamydomonas reinhardtii begins anew with the hatching of daughter cells, and the role of matrix metalloproteinases (MMPs) is known to be important in this process. In our previous study, we observed that a knockout mutant of the plant kinase belonging to the dual-specificity tyrosine phosphorylation-regulated kinase (DYRKP) formed a palmelloid structure and failed to hatch. QuestionsWhat is the role of DYRKP in microalgae? Specifically, why does the dyrkp mutant form a palmelloid structure? Palmelloid is usually observed in dividing cells or after exposure to stresses. We therefore hypothesized that the palmelloid phenotype observed in dyrkp mutant could either be due to a defect in cell hatching or due to an increased stress state in the mutant population. FindingsWe answered these questions by comparative studies in different culture conditions and by examining additional dyrkp knockout mutants generated by CRISPR-Cas9 in various background strains with more or less intact cell walls. Palmelloid formation in the dyrkp mutant was observed under optimal growth (mixo- or auto-trophic condition) and very low light conditions. Interestingly, unlike the parent strain, in which only cell wall fragments are observed in old cultures, the parental cell wall of the dyrkp mutant remained almost intact even after the release of daughter cells. Also, the cell division rate of the cell wall-less dyrkp mutants was similar to their background strain. These results suggest that dyrkp mutants have a problem in degrading the parental cell walls. Indeed, proteomic and transcriptomic analyses revealed reduced levels of protease families in the dyrkp mutant, and in particular with a significantly lower amount of several key members of the MMP family. Through the analysis of complementation lines, we confirmed that the DYRKP was required for strong and rapid expression of MMPs. Next stepsWe are pursuing research to understand what the phosphorylation clients of DYRKP are and how they regulate the expression of the MMPs identified in this study. One sentence summaryThe DYRKP kinase induces the expression of matrix metalloproteinases involved in the degradation of the parental cell wall, allowing prompt hatching of daughter cells after cell division.

plant biology↗

bioRxiv2023

Alka(e)nes contribute to membrane lipid homeostasis and resilience of photosynthesis to high light in cyanobacteria

Alka(e)nes are produced by many living organisms and exhibit diverse physiological roles, reflecting a high functional versatility. Alka(e)nes serve as water proof 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, a possible role in photosynthesis and chloroplast function remains elusive. In this study, we investigated the consequences of the absence of alka(e)nes on membrane lipid remodeling and photosynthesis using the cyanobacteria Synechocystis PCC6803 as a model organism. By following the dynamics of membrane lipids and the photosynthetic performance in strains defected and altered in alka(e)ne biosynthesis, we show that a profound remodeling of the membrane lipidome and carotenoid content occur in the absence of alka(e)nes, including a decrease in the membrane carotenoid content, a decrease in some digalactosyldiacylglycerol (DGDG) species and a parallel increase in monogalactosyldiacylglycerol (MGDG) species. Under high light, this effect is accompanied in alka(e)ne deficient strains by a higher susceptibility of photosynthesis and growth, the effect being reversed by expressing an algal photoenzyme producing alka(e)nes from fatty acids. We conclude that alka(e)nes play a crucial role in maintaining lipid homeostasis of photosynthetic membranes, thereby contributing to the proper functioning of photosynthesis, particularly under elevated light intensities. Significance statementWe used cyanobacteria as a model organism to explore the role of alka(e)nes related to photosynthesis. Our findings reveal that the absence of alka(e)nes induces alterations in the composition of membrane lipids and carotenoid content, resulting in an increased susceptibility of photosynthesis. By introducing a fatty acid photodecarboxylase to produce alkanes, we could reverse these effects, highlighting the critical role of alka(e)nes in maintaining lipid balance in photosynthetic membranes and ensuring efficient photosynthesis. Uncovering the physiological role of alka(e)nes provides insights to a better understanding of the widespread presence of genes encoding alka(e)nes-synthesizing enzymes in cyanobacteria and microalgae, organisms of major ecological and evolutionary importance in the global CO2 assimilation.

microbiology↗

bioRxiv2023

Algal CO2 capture is powered by alternative electron pathways of photosynthesis

On Earth, microalgae contribute to about half of global net photosynthesis. During photosynthesis, sunlight is converted into chemical energy (ATP and NADPH) used by metabolism to convert CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required for sustaining CO2 fixation, but the relative importance of each pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic and chloroplast to mitochondria electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that each pathway has the potential to energize substantial CO2 fixation, can compensate each other, and that the additional energy requirement to fix CO2 is more than 3 times higher than previous estimations. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast-mitochondria interaction being the most efficient, thus laying bioenergetic foundations for biotechnological improvement of CO2 capture.

plant biology↗

bioRxiv2023

The role of BST4 in the pyrenoid of Chlamydomonas reinhardtii

In many eukaryotic algae, CO2 fixation by Rubisco is enhanced by a CO2- 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 CO2. In the model alga Chlamydomonas reinhardtii (Chlamydomonas), the pyrenoid tubules have been proposed to be tethered to the Rubisco matrix by a bestrophin-like transmembrane protein, BST4. Here, we show that BST4 forms a complex that localizes to the pyrenoid tubules. A Chlamydomonas mutant impaired in the accumulation of BST4 (bst4) formed normal pyrenoid tubules and heterologous expression of BST4 in Arabidopsis thaliana did not lead to the incorporation of thylakoids into a reconstituted Rubisco condensate. Chlamydomonas bst4 mutant did not show impaired growth at air level CO2. By quantifying the non-photochemical quenching (NPQ) of chlorophyll fluorescence, we show that bst4 displays a transiently lower thylakoid lumenal pH during dark to light transition compared to control strains. When acclimated to high light, bst4 had sustained higher NPQ and elevated levels of light-induced H2O2 production. We conclude that BST4 is not a tethering protein, but rather is an ion channel involved in lumenal pH regulation possibly by mediating bicarbonate transport across the pyrenoid tubules. One-sentence summaryIn Chlamydomonas, the pyrenoid-localized bestrophin-like protein BST4 is a putative ion channel involved in pH regulation of the thylakoid lumen, possibly by mediating bicarbonate transport.

plant biology↗

bioRxiv2023

Cyclic and pseudo-cyclic electron pathways play antagonistic roles during nitrogen deficiency in Chlamydomonas reinhardtii

Nitrogen (N) scarcity is a frequently encountered situation that constrains global biomass productivity. In response to N deficiency, cell division stops and photosynthetic electron transfer is downregulated, while carbon storage is enhanced. However, the molecular mechanism downregulating photosynthesis during N deficiency and its relationship with carbon storage are not fully understood. The Proton Gradient Regulator-like 1 (PGRL1) controlling cyclic electron flow (CEF) and Flavodiiron proteins involved in pseudo-(CEF) are major players in the acclimation of photosynthesis. To determine the role of PGRL1 or FLV in photosynthesis under N deficiency, we measured photosynthetic electron transfer, oxygen gas exchange and carbon storage in Chlamydomonas pgrl1 and flvB knockout mutants. Under N deficiency, pgrl1 maintains higher net photosynthesis and O2 photoreduction rates, while flvB shows a similar response compared to control strains. Cytochrome b6f and PSI are maintained at a higher abundance in pgrl1. The photosynthetic activity of flvB and pgrl1 flvB double mutants decreases in response to N deficiency similar to the control strains. Furthermore, the preservation of photosynthetic activity in pgrl1 is accompanied by an increased accumulation of triacylglycerol depending on the genetic background. Taken together, our results suggest that in the absence of PGRL1-controlled CEF, FLV-mediated PCEF maintains net photosynthesis at a high level and that CEF and PCEF play antagonistic roles during N deficiency. It further illustrates how nutrient status and genetic makeup of a strain can affect the regulation of photosynthetic energy conversion in relation to carbon storage and provides new strategies for improving lipid productivity in algae. Significance statementNitrogen (N) deficiency, an often-encountered phenomenon in nature, results in growth arrest, downregulation of photosynthesis and massive carbon storage in microalgae. However, more mechanistic insights involved in tuning photosynthetic electron transfer during N deficiency are required. Here, we provide evidence that a well-conserved protein in chlorophytes, the Proton Gradient Regulator-like 1 (PGRL1), is a key regulator of photosynthesis during N deficiency. In its absence, cells exhibited sustained photosynthesis thanks to the Flavodiiron (FLV) proteins. We propose that both PGRL1 and FLV, by having antagonistic roles in N deficiency, manage the redox landscape, carbon storage and biomass production. Our work revolves around the current paradigm of photosynthesis regulation during N deficiency and provides a new framework for improving biomass production and carbon storage in microalgae for biotechnological purposes.

plant biology↗

bioRxiv2022

Boosting chloroplast ribosome biogenesis by a plastidial DEAD-box RNA helicase is critical for high light acclimation

Photosynthetic organisms have developed sophisticated strategies to fine-tune light energy conversion to meet the metabolic demand, thereby optimizing growth in fluctuating light environments. Although mechanisms such as energy dissipation, photosynthetic control, or the photosystem II (PSII) damage and repair have been widely studied, little is known about the regulation of protein synthesis capacity during light acclimation. By screening a Chlamydomonas reinhardtii insertional mutant library using chlorophyll fluorescence imaging, we isolated a high chlorophyll fluorescence mutant (hf0) defected in a gene encoding a putative plastid targeted DEAD-box RNA helicase called CreRH22. CreRH22 is rapidly induced upon illumination and belongs to the GreenCut, a set of proteins specific to photosynthetic organisms. While photosynthesis is slightly affected in the mutant under low light (LL), exposure to high light (HL) induces a marked decrease in both PSII and PSI, and a strong alteration of the light-induced gene expression pattern. These effects are explained by the inability of hf0 to increase plastid ribosome amounts under HL. We conclude that CreRH22, by promoting ribosomal RNA precursor maturation in a light-dependent manner, enables the assembly of extra-ribosomes required to synthesize photosystem subunits at a higher rate, a critical step in the acclimation of algae to HL.

plant biology↗

bioRxiv2021

Alternative electron pathways of photosynthesis drive the algal CO2 concentrating mechanism

Global photosynthesis consumes ten times more CO2 than net anthropogenic emissions, and microalgae account for nearly half of this consumption1. The great efficiency of algal photosynthesis relies on a mechanism concentrating CO2 (CCM) at the catalytic site of the carboxylating enzyme RuBisCO, thus enhancing CO2 fixation2. While many cellular components involved in the transport and sequestration of inorganic carbon (Ci) have been uncovered3,4, the way microalgae supply energy to concentrate CO2 against a thermodynamic gradient remains elusive4-6. Here, by monitoring dissolved CO2 consumption, unidirectional O2 exchange and the chlorophyll fluorescence parameter NPQ in the green alga Chlamydomonas, we show that the complementary effects of cyclic electron flow and O2 photoreduction, respectively mediated by PGRL1 and flavodiiron proteins, generate the proton motive force (pmf) required by Ci transport across thylakoid membranes. We demonstrate that the trans-thylakoid pmf is used by bestrophin-like Ci transporters and further establish that a chloroplast-to-mitochondria electron flow contributes to energize non-thylakoid Ci transporters, most likely by supplying ATP. We propose an integrated view of the CCM energy supply network, describing how algal cells distribute photosynthesis energy to power different Ci transporters, thus paving the way to the transfer of a functional algal CCM in plants towards improving crop productivity. One sentence summaryPhotosynthetic alternative electron flows and mitochondrial respiration drive the algal CO2 concentrating mechanism

plant biology↗

bioRxiv2020

Fatty acid photodecarboxylase is an ancient photoenzyme responsible for hydrocarbon formation in the thylakoid membranes of algae

ABSTRACTFatty acid photodecarboxylase (FAP) is one of the three enzymes that require light for their catalytic cycle (photoenzymes). FAP has been first identified in the green microalga Chlorella variabilis NC64A and belongs an algae-specific subgroup of the glucose-methanol-choline oxidoreductase family. While the FAP from Chlorella and its Chlamydomonas reinhardtii homolog CrFAP have demonstrated in vitro activity, their activity and physiological function have not been studied in vivo. Besides, the conservation of FAP activity beyond green microalgae remains hypothetical. Here, using a Chlamydomonas FAP knockout line (fap), we show that CrFAP is responsible for the formation of 7-heptadecene, the only hydrocarbon present in this alga. We further show that CrFAP is associated to the thylakoids and that 90% of 7-heptadecene is recovered in this cell fraction. In the fap mutant, photosynthesis activity was not affected under standard growth conditions but was reduced after cold acclimation. A phylogenetic analysis including sequences from Tara Ocean identified almost 200 putative FAPs and indicated that FAP was acquired early after primary endosymbiosis. Within Bikonta, FAP was kept in photosynthetic secondary endosymbiosis lineages but absent in those that lost the plastid. Characterization of recombinant FAPs from various algal genera (Nannochloropsis, Ectocarpus, Galdieria, Chondrus) provided experimental evidence that FAP activity is conserved in red and brown algae and is not limited to unicellular species. These results thus indicate that FAP has been conserved during evolution of most algal lineages when photosynthesis was kept and suggest that its function is linked to photosynthetic membranes.One sentence summary FAP is present in thylakoids and conserved beyond green algae.Competing Interest StatementThe authors have declared no competing interest.View Full Text

plant biology↗

bioRxiv2020

ACCLIMATION OF PHOTOSYNTHESIS TO THE ENVIRONMENT 1 regulates Photosystem II Supercomplex dynamics in response to light in Chlamydomonas reinhardtii

Photosynthetic organisms require acclimation mechanisms to regulate photosynthesis in response to light conditions. Here, two mutant alleles of ACCLIMATION OF PHOTOSYNTHESIS TO THE ENVIRONMENT 1 (ape1) have been characterized in Chlamydomonas reinhardtii. The ape1 mutants are photosensitive and show PSII photoinhibition during high light acclimation or under high light stress. The ape1 mutants retain more PSII super-complexes and have changes to thylakoid stacking relative to control strains during photosynthetic growth at different light intensities. The APE1 protein is found in all oxygenic phototrophs and encodes a 25 kDa thylakoid protein that interacts with the Photosystem II core complex as monomers, dimers and supercomplexes. We propose a model where APE1 bound to PSII supercomplexes releases core complexes and promotes PSII heterogeneity influencing the stacking of Chlamydomonas thylakoids. APE1 is a regulator in light acclimation and its function is to reduce over-excitation of PSII centres and avoid PSII photoinhibition to increase the resilience of photosynthesis to high light.

plant biology↗

bioRxiv2019

Algal photosynthesis converts nitric oxide into nitrous oxide

Nitrous oxide (N2O), a potent greenhouse gas in the atmosphere, is produced mostly from aquatic ecosystems, to which algae substantially contribute. However, mechanisms of N2O production by photosynthetic organisms are poorly described. Here, we show that the green microalga Chlamydomonas reinhardtii reduces NO into N2O using the photosynthetic electron transport. Through the study of C. reinhardtii mutants deficient in flavodiiron proteins (FLVs) or in a cytochrome p450 (CYP55), we show that FLVs contribute to NO reduction in the light, while CYP55 operates in the dark. Furthermore, NO reduction by both pathways is restricted to Chlorophytes, organisms particularly abundant in ocean N2O-producing hotspots. Our results provide a mechanistic understanding of N2O production in eukaryotic phototrophs and represent an important step toward a comprehensive assessment of greenhouse gas emission by aquatic ecosystems.\n\nOne sentence summaryGreen microalgae produce N2O using flavodiiron proteins in the light and a cytochrome P450 NO reductase in the dark.

plant biology↗

bioRxiv2019

An oomycete effector impairs autophagy in evolutionary distant organisms and favors host infection

An arsenal of effector proteins from plant pathogenic Phytophthora species manipulates their host from inside the cells. Phytophthora parasitica produces the effector AVH195 during an initial, biotrophic phase of infection. The protein transiently impairs plant immune-associated hypersensitive cell death in Nicotiana. ATG8 Interaction Motifs in the protein indicate that the effector targets the autophagic core machinery. We selected a photosynthetic microalga with a single copy ATG8 gene as an alternative model to dissect AVH195-induced autophagic perturbation. AVH195 slows down autophagic flux in Chlamydomonas reinhardtii thus promoting the accumulation of cargo-rich vesicles. In yeast, membrane-associated AVH195 interacts with ATG8 from Chlamydomonas and with different ATG8 isoforms from Arabidopsis thaliana. The overexpression of Avh195 in Arabidopsis promotes growth of both infecting P. parasitica and Hyaloperonospora arabidopsidis, an obligate biotroph. To our knowledge, this report provides first evidence that an oomycete effector non-selectively targets ATG8 in different organisms from the green lineage to slow down autophagic flux for infection.

plant biology↗