Rubisco mutants of Chlamydomonas reinhardtii display divergent photosynthetic parameters and lipid allocation

Influence of Cell Wall on Biomolecules Biosynthesis in Chlamydomonas reinhardtii Strains Exposed to Magnetic Fields

The application of magnetic fields (MF) has attracted the attention of researchers due to their efficiency to change cell metabolism. Chlamydomonas reinhardtii is a biotechnologically useful microalga with versatile metabolism that may be a valuable organism to study the effects of the MF in biology. Therefore, two C. reinhardtii strains, one with cell wall (2137) and other which lacks the cell wall (Wt-S1-cc4694), were evaluated that a new sensitivity factor in the analysis could be included. Comparative studies were undertaken with the two C. reinhardtii strains under the MF intensities of 0.005 mT (terrestrial MF - control), 11  and 20 mT. Results indicated that the physical cell wall barrier protected cells against the MF applied during the assays. Only with the highest MF applied (20 mT) a slight increase in lipid concentration in the cell wall strain was detected. The lowest growth of the strain that lacks cell wall (Wt-S1) indicated that these cells are under a negative effect. To cope with the two MF stresses conditions, Wt-S1 cells produced more pigments (chlorophylls and carotenoids) and lipids and enhanced the antioxidant defense system. The raise of these compounds under MF could potentially have a positive biotechnological impact on algal biomass.

Advances in Genetic Engineering in Improving Photosynthesis and Microalgal Productivity

Even though sunlight energy far outweighs the energy required by human activities, its utilization is a key goal in the field of renewable energies. Microalgae have emerged as a promising new and sustainable feedstock for meeting rising food and feed demand. Because traditional methods of microalgal improvement are likely to have reached their limits, genetic engineering is expected to allow for further increases in the photosynthesis and productivity of microalgae. Understanding the mechanisms that control photosynthesis will enable researchers to identify targets for genetic engineering and, in the end, increase biomass yield, offsetting the costs of cultivation systems and downstream biomass processing. This review describes the molecular events that happen during photosynthesis and microalgal productivity through genetic engineering and discusses future strategies and the limitations of genetic engineering in microalgal productivity. We highlight the major achievements in manipulating the fundamental mechanisms of microalgal photosynthesis and biomass production, as well as promising approaches for making significant contributions to upcoming microalgal-based biotechnology.

Ocean Acidification Alleviates Dwarf Eelgrass (Zostera noltii) Lipid Landscape Remodeling under Warming Stress

Coastal seagrass meadows provide a variety of essential ecological and economic services, including nursery grounds, sediment stabilization, nutrient cycling, coastal protection, and blue carbon sequestration. However, these ecosystems are highly threatened by ongoing climatic change. This study was aimed to understand how the dwarf eelgrass Zostera noltii leaf lipid landscapes are altered under predicted ocean warming (+4 °C) and hypercapnic (ΔpH 0.4) conditions. Warming and hypercapnic conditions were found to induce a severe reduction in the leaf total fatty acid, though the combined treatment substantially alleviated this depletion. The lipid discrimination revealed a significant increase in the relative monogalactosyldiacylglycerol (MGDG) content in both hypercapnic and warming conditions, allied to plastidial membrane stabilization mechanisms. Hypercapnia also promoted enhanced phosphatidylglycerol (PG) leaf contents, a mechanism often associated with thylakoid reinvigoration. In addition to changing the proportion of storage, galacto- and phospholipids, the tested treatments also impacted the FA composition of all lipid classes, with warming exposure leading to decreases in polyunsaturated fatty acids (PUFAs); however, the combination of both stress conditions alleviated this effect. The observed galactolipid and phospholipid PUFA decreases are compatible with a homeoviscous adaptation, allowing for the maintenance of membrane stability by counteracting excessive membrane fluidity. Neutral lipid contents were substantially increased under warming conditions, especially in C18 fatty acids (C18), impairing their use as substrates for fatty acylated derivatives essential for maintaining the osmotic balance of cells. An analysis of the phospholipid and galactolipid fatty acid profiles as a whole revealed a higher degree of discrimination, highlighting the higher impact of warming and the proposed stress alleviation effect induced by increased water-dissolved CO2 availability. Still, it is essential to remember that the pace at which the ocean is warming can overcome the ameliorative capacity induced by higher CO2 availability, leaving seagrasses under severe heat stress beyond their lipid remodeling capacity.

Photosynthesis and pigment production: elucidation of the interactive effects of nutrients and light on Chlamydomonas reinhardtii

Chlamydomonas reinhardtii produces a variety of compounds that can be beneficial to human and animal health. Among these compounds, application of photosynthetic pigments, such as chlorophylls and carotenoids, has gained considerable interest in numerous industries. A better understanding on the interactive effects of essential nutrients and light on microalgal physiology and pigment production would be beneficial in improving cultivation strategies. Therefore, this study evaluated biomass, carotenoid and chlorophyll yield and the following fluorescence parameters: quantum yield in PS II [Y(II)] and electron transport rate (ETR) using response surface methodology (RSM). The F_v/F_m, Y(NO) and Y(NPQ) were also monitored; however, no significant relationship was observed. From the investigation it was apparent that nitrogen and carbon; as well as the interactive effects of (nitrogen and carbon) and (carbon and light irradiance) were significant factors. The model predicted the optimum conditions for maximum carotenoids (8.15 ± 0.389 mg g^-1) were 08.7 mol l^-1 of nitrogen, 0.2 mol l^-1 and 50 μmol photon m^-2 s^-1 of light irradiance. While maximum chlorophyll (33.6 ± 0.854 mg g^-1) required a higher nitrogen (11.21 mol l^-1). The photosynthetic parameters [Y(II), ETR] was correlated with the primary pigments and biomass production. Increased photosynthetic activity was associated with high carbon and light. The Y(II)and ETR of PSII under these conditions were 0.2 and ~ 14, respectively. This approach was accurate in developing the model, optimizing factors and analysing interaction effects. This study served to provide a better understanding on the interactions between factors influencing pigment biosynthesis and photosynthetic performance of Chlamydomonas reinhardtii.

Heavy Metal Pre-Conditioning History Modulates Spartina patens Physiological Tolerance along a Salinity Gradient

Land salinization, resulting from the ongoing climate change phenomena, is having an increasing impact on coastal ecosystems like salt marshes. Although halophyte species can live and thrive in high salinities, they experience differences in their salt tolerance range, being this a determining factor in the plant distribution and frequency throughout marshes. Furthermore, intraspecific variation to NaCl response is observed in high-ranging halophyte species at a population level. The present study aims to determine if the environmental history, namely heavy metal pre-conditioning, can have a meaningful influence on salinity tolerance mechanisms of Spartina patens, a highly disperse grass invader in the Mediterranean marshes. For this purpose, individuals from pristine and heavy metal contaminated marsh populations were exposed to a high-ranging salinity gradient, and their intraspecific biophysical and biochemical feedbacks were analyzed. When comparing the tolerance mechanisms of both populations, S. patens from the contaminated marsh appeared to be more resilient and tolerant to salt stress, this was particularly present at the high salinities. Consequently, as the salinity increases in the environment, the heavy metal contaminated marsh may experience a more resilient and better adapted S. patens community. Therefore, the heavy metal pre-conditioning of salt mash populations appears to be able to create intraspecific physiological variations at the population level that can have a great influence on marsh plant distribution outcome.

An apoplastic fluid extraction method for the characterization of grapevine leaves proteome and metabolome from a single sample

The analysis of complex biological systems keeps challenging researchers. The main goal of systems biology is to decipher interactions within cells, by integrating datasets from large scale analytical approaches including transcriptomics, proteomics and metabolomics and more specialized 'OMICS' such as epigenomics and lipidomics. Studying different cellular compartments allows a broader understanding of cell dynamics. Plant apoplast, the cellular compartment external to the plasma membrane including the cell wall, is particularly demanding to analyze. Despite our knowledge on apoplast involvement on several processes from cell growth to stress responses, its dynamics is still poorly known due to the lack of efficient extraction processes adequate to each plant system. Analyzing woody plants such as grapevine raises even more challenges. Grapevine is among the most important fruit crops worldwide and a wider characterization of its apoplast is essential for a deeper understanding of its physiology and cellular mechanisms. Here, we describe, for the first time, a vacuum-infiltration-centrifugation method that allows a simultaneous extraction of grapevine apoplastic proteins and metabolites from leaves on a single sample, compatible with high-throughput mass spectrometry analyses. The extracted apoplast from two grapevine cultivars, Vitis vinifera cv 'Trincadeira' and 'Regent', was directly used for proteomics and metabolomics analysis. The proteome was analyzed by nanoLC-MS/MS and more than 700 common proteins were identified, with highly diverse biological functions. The metabolome profile through FT-ICR-MS allowed the identification of 514 unique putative compounds revealing a broad spectrum of molecular classes.

Lipid landscape remodelling in Sarcocornia fruticosa green and red physiotypes

Under certain abiotic conditions (elevated irradiance, temperature and sediment salinity) observed mostly during the Mediterranean summer, the halophyte Sarcocornia fruticosa suffers a metabolic shift evidenced by a red coloration, evidencing the presence of two physiotypes (green and red). Previous works indicated that this metabolic shift has severe implications in the primary photochemistry of this species, impairing the light and carbon harvesting. Under stress plants have lower light use efficiencies and are more prone to photoinhibition, and thus this metabolic shift is essential for this species to deal with the high light intensities characteristic from this time of the year. Nevertheless, the fatty acid and lipid remodelling in green and red S. fruticosa physiotypes was not previously evaluated nor its relations with this metabolic shift. The evaluation of the lipid landscape suggests several lipid and fatty acid remodelling when comparing both red and green physiotype, as strategies to overcome stress. The galactolipids of the red physiotype suffer several changes aiming to keep chloroplast membrane structural and functional stability during water stress and can also be related to an improvement of the plants response to osmotic stress. At the phospholipid level, a readjustment of its fatty acid profiles was also observable. This remodelling allows the plants to adjust membrane fluidity the imposed osmotic stress, being this action transversal to choroplastidial, extraplastidial, and involves the action of the different phospholipids. Additionally, neutral lipids (NLs) also appear to play a role in osmotic stress adaptation, with an increase content in C18 fatty acids in the red physiotype. The resulting lipid landscape in both physiotypes presents very specific signatures that can be used as biomarkers to track this kind of metabolic shifts, in future studies with similar species.

Marine heat waves alter gene expression of key enzymes of membrane and storage lipids metabolism in Phaeodactylum tricornutum

Across the globe, heat waves are getting more intense and frequent. Diatoms are a major group of microalgae at the base of the marine food webs and an important source of long chain polyunsaturated fatty acids that are transferred through the food web. The present study investigates the possible impacts of temperature increase on lipid classes and expression of genes encoding enzymes related to lipid metabolism in Phaeodactylum tricornutum. The heat wave exposure caused an increase in the relative amounts of plastidial lipids such as the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulphoquinovosyldiacylglycerol (SQDG) in parallel with a decrease in the neutral lipid fraction, which includes triacylglycerols. In agreement, gene expression analyses revealed an up-regulation of a gene encoding one MGDG synthase and down-regulation of a diacylglycerol acyltransferase (DGAT), a key enzyme in triacylglycerol synthesis. Our results show that heat waves not only negatively impact the abundance of unsaturated fatty acids such as eicosapentaenoic acid (20:5n-3, EPA) and hexadecatrienoic acid (16:3n-4) as observed by the decrease in their relative abundance in MGDG and neutral lipids, respectively, but also induce changes in the relative amounts of the diverse membrane lipids as well as the proportion of membrane/storage lipids. The expression study of key genes indicates that some of the aforementioned alterations are regulated at the transcription level whereas others appear to be post-transcriptional. The changes observed in plastidial lipids are related to negative impacts on the photosynthesis.

The leaf lipid composition of ectomycorrhizal oak plants shows a drought-tolerance signature

Ectomycorrhizas have been reported to increase plant tolerance to drought. However, the mechanisms involved are not yet fully understood. Membranes are the first targets of degradation during drought, and growing evidences support a role for membrane lipids in plant tolerance and adaptation to drought. We have previously shown that improved tolerance of ectomycorrhizal oak plants to drought could be related to leaf membrane lipid metabolism, namely through an increased ability to sustain fatty acid content and composition, indicative of a higher membrane stability under stress. Here, we analysed in deeper detail the modulation of leaf lipid metabolism in oak plants mycorrhized with Pisolithus tinctorius and subjected to drought stress. Results show that mycorrhizal plants show patterns associated with water deficit tolerance, like a higher content of chloroplast lipids, whose levels are maintained upon drought stress. Likewise, mycorrhizal plants show increased levels of unsaturated fatty acids in the chloroplast phosphatidylglycerol lipid fraction. As a common response to drought, the digalactosyldiacyloglycerol/monogalactosyldiacyloglycerol ratio increased in the non-mycorrhizal plants, but not in the mycorrhizal plants, associated to smaller alterations in the expression of galactolipid metabolism genes, indicative of a higher drought tolerance. Under drought, inoculated plants showed increased expression of genes involved in neutral lipids biosynthesis, which could be related to an increased ability to tolerate drought stress. Overall, results from this study provide evidences of the involvement of lipid metabolism in the response of ectomycorrhizal plants to water deficit and point to an increased ability to maintain a stable chloroplast membrane functional integrity under stress.

Preliminary diversity assessment of an undervalued tropical bean (Lablab purpureus (L.) Sweet) through fatty acid profiling

Several large-scale metabolic profiling studies have been directed to prospect crops with a major focus on yield-related traits and, ultimately, with the definition of specific markers for plant selection in breeding programs. However, some of these technologies are expensive, time-consuming and not easily feasible for a quick approach. Fatty acid profiling was described as reliable biomarkers and as a chemotaxonomic tool allowing to study not only the diversity in germplasm collections but also to discriminate their geographic origin. We have used fatty acids profiling for a preliminary assessment of Lablab purpureus (L.) Sweet (hyacinth bean) diversity and landraces discrimination. Hyacinth bean displays an enormous variability of agro-morphological traits, probably linked to the multi-purpose uses in different regions, i.e. as pulse, or as food with nutraceutical potential (Africa and Asia), forage (Africa and Australia) and ornamental (Europe and USA). Only two forage cultivars are widely marketed, cv. Rongai and cv. Highworth, with several landraces remaining to be addressed in terms of diversity. We show that fatty acids profiling was able to distinguish landraces, which display shared fatty acids with cultivars from the center of hyacinth bean diversity origin (East Africa). We propose that fatty acid profiling is a tool that may be used not only for nutritional value assessment but also as a chemodiversity tool in crop research.