Parthenosporophytes of the brown alga Ectocarpus siliculosus exhibit sex-dependent differences in thermotolerance as well as fatty acid and sterol composition

Evidence of sterility of the male sporophytes of the brown alga Saccharina japonica (Phaeophyceae) in culture irrespective of their ploidy levels

Monoclonal female gametophytes of Saccharina japonica, when cultured independently, can develop into female sporophytes. Previous research has shown that the chromosomes in female sporophytes of S. japonica may naturally duplicate, forming diploids, and these diploid female sporophytes are capable of forming sori and releasing zoospores. In contrast, male sporophytes derived from culturing monoclonal male gametophytes failed to form sori and produce meiospores; thus, it was hypothesized that these male sporophytes are haploid and unable to perform meiotic division. In order to explore whether the chromosomes in male sporophytes can naturally duplicate and whether such diploid male sporophytes can effectively form sori and produce meiospores, we obtained 62 male sporophytes and cultivated them into adults. Only male-specific DNA markers were detected in all of these male sporophytes, indicating their male nature. Ten microsatellite markers were used to estimate the relatedness of the parental gametophytes and the corresponding sporophytes. Results revealed that the genotypes of the male sporophytes matched exactly with the corresponding male gametophytes. Both diploid and haploid sporophytes were detected in these 62 male sporophytes when analyzed by flow cytometry. After 16 months of cultivation, none of the male sporophytes formed sori regardless of their ploidy. As controls, both female and hybrid sporophytes developed sori and released viable zoospores. These findings suggest that the sterility of male sporophytes in S. japonica is not related to their ploidy; rather, it is attributed to the absence of essential elements for sori formation that may be present only in the female.

Lipoxygenase pathway in brown algae: The biosynthesis of novel oxylipins 'ectocarpins' by hydroperoxide bicyclase CYP5164A3 of Ectocarpus siliculosus

The sequence encoding the CYP5164A3 of the brown alga Ectocarpus siliculosus (Stramenopiles, SAR) was heterologously expressed in E. coli cells. The resulting recombinant CYP74 clan-related protein CYP5164A3 possessed a selective activity towards the α-linolenic acid 13(S)-hydroperoxide (13-HPOTE) and eicosapentaenoic acid 15(S)-hydroperoxide (15-HPEPE). The major products were the heterobicyclic oxylipins. For instance, the 13-HPOTE was converted into plasmodiophorols A, B, and C formed at about 14:3:2 ratio. Plasmodiophorols A-C have been recently described as the products of enzyme hydroperoxide bicyclase CYP50918A1 of cercozoan Plasmodiophora brassicae (Rhizaria, SAR). Furthermore, an unknown compound 1 was detected. Purified product 1 (Me) was identified as a novel substituted 3-propenyl-6-oxabicyclo[3.1.0]hexane based on its MS and NMR spectral data. Conversion of 15-HPEPE by CYP5164A3 resulted in products 7 and 8, analogous to plasmodiophorols A and B. This work uncovered the CYP5164A3 as the first hydroperoxide bicyclase in brown algae. Apparently, this enzyme plays a crucial role in the biosynthesis of heterobicyclic oxylipins like hybridalactone, ecklonilactones, and related natural products, widespread in brown algae.

Phytosterol Profiles, Genomes and Enzymes - An Overview

The remarkable diversity of sterol biosynthetic capacities described in living organisms is enriched at a fast pace by a growing number of sequenced genomes. Whereas analytical chemistry has produced a wealth of sterol profiles of species in diverse taxonomic groups including seed and non-seed plants, algae, phytoplanktonic species and other unicellular eukaryotes, functional assays and validation of candidate genes unveils new enzymes and new pathways besides canonical biosynthetic schemes. An overview of the current landscape of sterol pathways in the tree of life is tentatively assembled in a series of sterolotypes that encompass major groups and provides also peculiar features of sterol profiles in bacteria, fungi, plants, and algae.

The Absence of Hydrodynamic Stress Promotes Acquisition of Freezing Tolerance and Freeze-Dependent Asexual Reproduction in the Red Alga 'Bangia' sp. ESS1

The ebb tide causes calm stress to intertidal seaweeds in tide pools; however, little is known about their physiological responses to loss of water movement. This study investigated the effects of static culture of ‘Bangia’ sp. ESS1 at 15 °C on tolerance to temperature fluctuation. The freezing of aer-obically cultured thalli at −80 °C for 10 min resulted in the death of most cells. By contrast, statically cultured thalli acquired freezing tolerance that increased cell viability after freeze–thaw cycles, although they did not achieve thermotolerance that would enable survival at the lethal temperature of 32 °C. Consistently, the unsaturation of membrane fatty acids occurred in static culture. Notably, static culture of thalli enhanced the release of asexual spores after freeze-and-thaw treatment. We conclude that calm stress triggers both the acquisition of freezing tolerance and the promotion of freezing-dependent asexual reproduction. These findings provide novel insights into stress toler-ance and the regulation of asexual reproduction in Bangiales.

Semi-Quantitative Targeted Gas Chromatography-Mass Spectrometry Profiling Supports a Late Side-Chain Reductase Cycloartenol-to-Cholesterol Biosynthesis Pathway in Brown Algae

Sterols are biologically important molecules that serve as membrane fluidity regulators and precursors of signaling molecules, either endogenous or involved in biotic interactions. There is currently no model of their biosynthesis pathways in brown algae. Here, we benefit from the availability of genome data and gas chromatography-mass spectrometry (GC-MS) sterol profiling using a database of internal standards to build such a model. We expand the set of identified sterols in 11 species of red, brown, and green macroalgae and integrate these new data with genomic data. Our analyses suggest that some metabolic reactions may be conserved despite the loss of canonical eukaryotic enzymes, like the sterol side-chain reductase (SSR). Our findings are consistent with the principle of metabolic pathway drift through enzymatic replacement and show that cholesterol synthesis from cycloartenol may be a widespread but variable pathway among chlorophyllian eukaryotes. Among the factors contributing to this variability, one could be the recruitment of cholesterol biosynthetic intermediates to make signaling molecules, such as the mozukulins. These compounds were found in some brown algae belonging to Ectocarpales, and we here provide a first mozukulin biosynthetic model. Our results demonstrate that integrative approaches can already be used to infer experimentally testable models, which will be useful to further investigate the biological roles of those newly identified algal pathways.

Suitability of stationary phase for LC analysis of biomolecules

Biologically active compounds such as carotenoids/isoprenoids, vitamins, steroids, saponins, sugars, long chain fatty acids, and amino acids play a very important role in coordinating functions in living organisms. Determination of those substances is indispensable in advanced biological sciences. Engineered stationary phase in LC for the analysis of biomolecules has become easier with the development of chromatographic science. In general, C₁₈ column is being used for routine analysis but specific columns are being used for specific molecule. Monolithic columns are found to have higher efficiency than normal column. Among recent introduction, triacontyl stationary phases, designed for the separation of carotenoid isomers, are widely used for the estimation of carotenoids. In comparison to conventional C₁₈ phases, C₃₀ phases exhibited superior shape selectivity for the separation of isomers of carotenoids. It is also found useful for better elution and analysis of tocopherols, vitamin K, sterols, and fatty acids. Vitamin K, E, and their isomers are also successfully resoluted and analyzed by using C₃₀ column. Amino bonded phase column is specifically used for better elution of sugars, whereas phenyl columns are suitable for the separation and analysis of curcuminoids and taxol. Like triacontyl stationary phase, pentafluorophenyl columns are also used for the separation and analysis of carotenoids. Similarly, HILIC column are best suited for sugar analysis. All the stationary phases are made possible to resolute and analyze the target biomolecules better, which are the future of liquid chromatography. The present article focuses on the differential interaction between stationary phase and target biomolecules. The applicability of these stationary phases are reported in different matrices.

Heat-stress Memory is Responsible for Acquired Thermotolerance in Bangia fuscopurpurea

The environmental stresses that sessile organisms experience usually fluctuate dramatically and are often recurrent. Terrestrial plants can acquire memory of exposure to sublethal heat stress to acquire thermotolerance and survive subsequent lethal high-temperature stress; however, little is known concerning whether seaweeds acquire thermotolerance via heat-stress memory. We have demonstrated that the red seaweed Bangia fuscopurpurea can indeed acquire memory of sublethal high-temperature stress, resulting in the acquisition of thermotolerance that protects against subsequent lethal high-temperature stress. Moreover, the maintenance of heat-stress memory was associated with a slight increase in the saturation level of membrane fatty acids. This suggests that the modification of membrane fluidity via changes in membrane fatty acid composition is involved in the establishment and maintenance of heat-stress memory in B. fuscopurpurea. These findings provide insights into the physiological survival and growth strategies of sessile red seaweeds to cope with recurrent changes in environmental conditions.