Fatty Acid Production and Direct Acyl Transfer through Polar Lipids Control TAG Biosynthesis during Nitrogen Deprivation in the Halotolerant Alga .

The aims of this work were to evaluate the contribution of the free fatty acid (FA) pool to triacylglyceride (TAG) biosynthesis and to try to characterize the mechanism by which FA are assimilated into TAG in the green alga . A time-resolved lipidomic analysis showed that nitrogen (N) deprivation induces a redistribution of total lipidome, particularly of free FA and major polar lipid (PL), in parallel to enhanced accumulation of polyunsaturated TAG. The steady-state concentration of the FA pool, measured by prolonged C-bicarbonate pre-labeling, showed that N deprivation induced a 50% decrease in total FA level within the first 24 h and up to 85% after 96 h.

A hypothesis about the origin of carotenoid lipid droplets in the green algae Dunaliella and Haematococcus.

Hypercarotenogenesis in green algae evolved by mutation of PSY that increased its transcription at high light, disintegration of the eyespot in Dunaliella and acquisition of the capacity to export carotenoids from chloroplasts in Haematococcus. Carotenoids (Car) are lipid-soluble pigments synthesized in plants, algae, bacteria and fungi. Car have strong antioxidative properties and as such are utilized to reduce the danger of different diseases in humans.

Triacylglycerol is produced from starch and polar lipids in the green alga Dunaliella tertiolecta.

The halotolerant green alga Dunaliella tertiolecta accumulates starch and triacylglycerol (TAG) amounting to 70% and 10-15% of total cellular carbon, respectively, when exposed to nitrogen (N) deprivation. The purpose of this study was to clarify the inter-relationships between the biosynthesis of TAG, starch, and polar lipids (PLs) in this alga. Pulse labeling with [14C]bicarbonate was utilized to label starch and [14C]palmitic acid (PlA) to label lipids.

Novel 9-cis/all-trans β-carotene isomerases from plastidic oil bodies in Dunaliella bardawil catalyze the conversion of all-trans to 9-cis β-carotene.

We identified and demonstrated the function of 9-cis/all-trans β-carotene isomerases in plastidic globules of Dunaliella bardawil, the species accumulating the highest levels of 9-cis β-carotene that is essential for humans. The halotolerant alga Dunaliella bardawil is unique in that it accumulates under light stress high levels of β-carotene in plastidic lipid globules. The pigment is composed of two major isomers: all-trans β-carotene, the common natural form of this pigment, and 9-cis β-carotene.

Acetyl-CoA synthetase is activated as part of the PDH-bypass in the oleaginous green alga Chlorella desiccata.

In a recent study, it has been shown that biosynthesis of triacylglycerol (TAG) in the oleaginous green alga Chlorella desiccata is preceded by a large increase in acetyl-coenzyme A (Ac-CoA) levels and by upregulation of plastidic pyruvate dehydrogenase (ptPDH). It was proposed that the capacity to accumulate high TAG critically depends on enhanced production of Ac-CoA. In this study, two alternative Ac-CoA producers-plastidic Ac-CoA synthase (ptACS) and ATP citrate lyase (ACL)-are shown to be upregulated prior to TAG accumulation under nitrogen deprivation in the oleaginous species C.

Enhanced acetyl-CoA production is associated with increased triglyceride accumulation in the green alga Chlorella desiccata.

Triglycerides (TAGs) from microalgae can be utilized as food supplements and for biodiesel production, but little is known about the regulation of their biosynthesis. This work aimed to test the relationship between acetyl-CoA (Ac-CoA) levels and TAG biosynthesis in green algae under nitrogen deprivation. A novel, highly sensitive liquid chromatography mass spectrometry (LC-MS/MS) technique enabled us to determine the levels of Ac-CoA, malonyl-CoA, and unacetylated (free) CoA in green microalgae.

Proteome analysis of cytoplasmatic and plastidic β-carotene lipid droplets in Dunaliella bardawil.

The halotolerant green alga Dunaliella bardawil is unique in that it accumulates under stress two types of lipid droplets: cytoplasmatic lipid droplets (CLD) and β-carotene-rich (βC) plastoglobuli. Recently, we isolated and analyzed the lipid and pigment compositions of these lipid droplets. Here, we describe their proteome analysis.

Iron uptake mechanism in the chrysophyte microalga Dinobryon.

The mechanism of iron uptake in the chrysophyte microalga Dinobryon was studied. Previous studies have shown that iron is the dominant limiting elements for growth of Dinobryon in the Eshkol reservoir in northern Israel, which control its burst of bloom. It is demonstrated that Dinobryon has a light-stimulated ferrireductase activity, which is sensitive to the photosynthetic electron transport inhibitor DCMU and to the uncoupler CCCP.

Origin of β-carotene-rich plastoglobuli in Dunaliella bardawil.

The halotolerant microalgae Dunaliella bardawil accumulates under nitrogen deprivation two types of lipid droplets: plastoglobuli rich in β-carotene (βC-plastoglobuli) and cytoplasmatic lipid droplets (CLDs). We describe the isolation, composition, and origin of these lipid droplets. Plastoglobuli contain β-carotene, phytoene, and galactolipids missing in CLDs.

LIGHT-INDUCED OIL GLOBULE MIGRATION IN HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE).

Astaxanthin-rich oil globules in Haematococcus pluvialis display rapid light-induced peripheral migration that is unique to this organism and serves to protect the photosynthetic system from excessive light. We observed rapid light-induced peripheral migration that is associated with chlorophyll fluorescence quenching, whereas the recovery was slow. A simple assay to follow globule migration, based on chlorophyll fluorescence level has been developed.

Characterization of major lipid droplet proteins from Dunaliella.

Many green algal species can accumulate large amounts of triacylglycerides (TAG) under nutrient deprivation, making them a potential source for production of biodiesel. TAG are organized in cytoplasmic lipid bodies, which contain a major lipid droplet protein termed MLDP. Green algae MLDP differ in sequence from plant oleosins and from animal perilipins, and their structure and function are not clear.

Kinetic anomalies in the interactions of Nile red with microalgae.

Nile red (NR) is a popular fluorescent indicator to visualize lipid bodies in intact cells and has been extensively utilized to monitor triglyceride accumulation in microalgae. Typically, addition of NR to algae results in a rapid fluorescence enhancement followed by fluorescence quenching. NR fluorescence rise can be resolved into two kinetic phases: a fast phase (P₁, sec), monitored at 525 nm/630 nm, followed by a slower phase (P₂, min), monitored at 488 nm/575 nm.

Isolation of a novel oil globule protein from the green alga Haematococcus pluvialis (Chlorophyceae).

Cytoplasmic oil globules of Haematococcus pluvialis (Chlorophyceae) were isolated and analyzed for pigments, lipids and proteins. Astaxanthin appeared to be the only pigment deposited in the globules. Triacyglycerols were the main lipids (more than 90% of total fatty acids) in both the cell-free extract and in the oil globules.

Salt-induced changes in the plasma membrane proteome of the halotolerant alga Dunaliella salina as revealed by blue native gel electrophoresis and nano-LC-MS/MS analysis.

The halotolerant alga Dunaliella salina is a recognized model photosynthetic organism for studying plant adaptation to high salinity. The adaptation mechanisms involve major changes in the proteome composition associated with energy metabolism and carbon and iron acquisition. To clarify the molecular basis for the remarkable resistance to high salt, we performed a comprehensive proteomics analysis of the plasma membrane.

Effects of iron deficiency on iron binding and internalization into acidic vacuoles in Dunaliella salina.

Uptake of iron in the halotolerant alga Dunaliella salina is mediated by a transferrin-like protein (TTf), which binds and internalizes Fe(3+) ions. Recently, we found that iron deficiency induces a large enhancement of iron binding, which is associated with accumulation of three other plasma membrane proteins that associate with TTf. In this study, we characterized the kinetic properties of iron binding and internalization and identified the site of iron internalization.

A multicopper ferroxidase involved in iron binding to transferrins in Dunaliella salina plasma membranes.

The halotolerant alga Dunaliella salina is unique among plants in that it utilizes a transferrin (TTf) to mediate iron acquisition (Fisher, M., Zamir, A., and Pick, U.

Phosphorylation of SPICK2, an AKT2 channel homologue from Samanea motor cells.

SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus.

A chlorophyll a/b-binding protein homolog that is induced by iron deficiency is associated with enlarged photosystem I units in the eucaryotic alga Dunaliella salina.

Adaptation of the halotolerant alga Dunaliella salina to iron deprivation involves extensive changes of chloroplast morphology, photosynthetic activities, and induction of a major 45-kDa chloroplast protein termed Tidi. Partial amino acid sequencing of proteolytic peptides suggested that Tidi resembles chlorophyll a/b-binding proteins which compose light-harvesting antenna complexes (LHC) (Varsano, T., Kaftan, D.

Enhanced photosynthesis and redox energy production contribute to salinity tolerance in Dunaliella as revealed by homology-based proteomics.

Salinity is a major limiting factor for the proliferation of plants and inhibits central metabolic activities such as photosynthesis. The halotolerant green alga Dunaliella can adapt to hypersaline environments and is considered a model photosynthetic organism for salinity tolerance. To clarify the molecular basis for salinity tolerance, a proteomic approach has been applied for identification of salt-induced proteins in Dunaliella.

The respiratory inhibitor antimycin A specifically binds Fe(III) ions and mediates utilization of iron by the halotolerant alga Dunaliella salina (Chlorophyta).

It is demonstrated that Antimycin A (AA), a respiratory inhibitor produced by Streptomyces bacteria, forms lipophylic complexes with Fe(III) ions. Spectroscopic titration indicates that Fe(III) ions interact with 2AA molecules. At growth-limiting Fe concentrations, AA mediates Fe uptake and promotes growth and chlorophyll synthesis better than other Fe chelators in the halotolerant alga Dunaliella salina.

Temperature-regulated expression of a glycine-rich RNA-binding protein in the halotolerant alga Dunaliella salina.

Acclimation of the halotolerant alga Dunaliella salina to low temperature induced the accumulation of a 12.4 kDa protein (DsGRP-1) and reduction of a 13.1 kDa protein (DsGRP-2).

A transferrin-like protein that does not bind iron is induced by iron deficiency in the alga Dunaliella salina.

Iron deficiency induces two major transferrin-like proteins in the plasma membrane (Pm) of the halotolerant alga Dunaliella salina. TTf, a 150-kDa protein, previously identified as a salt-induced triplicated transferrin, having iron-binding characteristics resembling animal transferrins, and a 100-kDa protein designated idi-100 (for iron-deficiency-induced 100 kDa protein). According to the predicted amino acid sequence of idi-100, it is only 30% identical to TTf and differs from it in having two, rather than three, homologous internal repeats and in a lower conservation of canonical iron/bicarbonate binding residues.

Cold-acclimation protects photosystem II against freezing damage in the halotolerant alga Dunaliella salina.

Cold-acclimation (CA) of the halotolerant alga Dunaliella was inhibited by light and by high salt. CA was associated with enhanced resistance to freezing in saline growth solutions, as manifested by protection of photosynthetic oxygen evolution and by reduced permeabilisation of the plasma membrane. Oxygen evolution activity in isolated chloroplasts was not affected by freezing, but was inhibited by high salt and the inhibition could be reversed or protected by glycerol.