Search

The red macroalga Pyropia yezoensis is an economically important seaweed widely cultured in Asian countries and is a model organism for molecular biological and commercial research. This species is unique in that it utilizes both phycobilisomes and transmembrane light-harvesting proteins as its antenna system. Here, one of the genes of P. yezoensis (PyLHCI) was selected for introduction into its genome to overexpress PyLHCI. However, the co-suppression phenomenon occurred. This is the first documentation of co-suppression in algae, in which it exhibits a different mechanism from that in higher plants. The transformant (T1) was demonstrated to have higher phycobilisomes and lower LHC binding pigments, resulting in a redder color, higher sensitivity to salt stress, smaller in size, and slower growth rate than the wildtype (WT). The photosynthetic performances of T1 and WT showed similar characteristics; however, P700 reduction was slower in T1. Most importantly, T1 could release a high percentage of carpospores in young blades to switch generation during its life cycle, which was rarely seen in WT. The co-suppression of PyLHCI revealed its key roles in light harvesting, stress resistance, and generation alternation (generation switch from gametophytes to sporophytes, and reproduction from asexual to sexual).

Phytoene and astaxanthin are 2 important carotenoids in the green alga Haematococcus pluvialis. Under environmental stress, the synthesis of phytoene in H. pluvialis increases significantly, and phytoene is converted to astaxanthin through enzymatic catalysis. This paper analyzes the relationship between astaxanthin and phytoene accumulation in carotenoid synthesis pathways under different concentrations of sodium acetate (NaAc) by high-performance liquid chromatography. The highest concentrations of phytoene and astaxanthin were observed at the NaAc concentration of 6 g l-1 on the 12th day of induction. The highest astaxanthin concentration achieved was 2.26 ± 0.28%. Therefore, we concluded that 6 g l-1 NaAc and induction for 12 d provided the optimal inducing conditions for astaxanthin accumulation in H. pluvialis. psy, pds, lcyB, β-carotene ketolase crtw, and crtz, which are genes related to phytoene and astaxanthin synthesis, were cloned and studied at the transcriptional level. crtw and crtz were continuously up-regulated since the first day of induction, while psy, pds, and lcyB were continuously up-regulated starting on the 3rd day of induction. These findings are important for enhancing our understanding of the mechanism of accumulation of phytoene and astaxanthin in H. pluvialis and provide a foundation for identifying the induction conditions necessary for optimizing astaxanthin production and increasing astaxanthin yields.

Haematococcus pluvialis has attracted attention due to its ability to produce astaxanthin, which has many functions such as antioxidation and anticancer. In order to further understand its nitrogen metabolism, the transcription levels and the enzyme levels of glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) in the process of nitrogen assimilation were studied under different nitrogen concentrations after cloning their cDNA sequences. The cloned cDNA sequence of gs is 1438 bp, including a 178-bp 5′ untranslatable region (UTR), a 114-bp 3′ UTR, and a 1146-bp open reading frame (ORF), which encodes a protein of 381 amino acids. The gogat had a total cDNA of 4931 bp, including a 17-bp 5′ UTR and a 4914-bp ORF, which encodes a protein of 1637 amino acids. The gdh had a total cDNA of 1529 bp, including 131-bp 3′ UTR and a 1398-bp ORF, which encodes a protein of 465 amino acids. During cultivation the transcription levels of the three genes fluctuated slightly during the first 4 days and then declined significantly. At the fourth day, the highest level of the transcription of the three genes was at the nitrogen concentration of 1000 mg L−1. The enzyme level also fluctuated with culture time, which is positively correlated with the transcription level. This study may lay foundation for optimization of nitrogen concentration for cultivation of H. pluvialis.

Haematococcus pluvialis is an economic microalga to produce astaxathin. To study the nitrogen metabolic process of H. pluvialis, the transcription level and enzyme content of nitrite reductase at different nitrate and phosphorus concentrations were studied. In this research, nitrite reductase gene (nir) was first cloned from H. pluvialis, which consists of 5592 nucleotides and includes 12 introns. The cDNA ORF is 1776 bp, encoding a 592 amino acid protein with two conserved domains. Phylogenetic analysis showed that the nir gene in H. pluvialis had the highest affinity with other freshwater green algae. Nitrogen and phosphorus play an important role in the growth of H. pluvialis. The single factor experiments of nitrogen on growth conditions showed that the group with 0.2 g/L NaNO3 had a relative high biomass. The single factor experiments of phosphorus on growth conditions showed that the group with 0.06 g/L K2HPO4 had a relative high biomass. The transcription level and enzymatic activity of nitrite reductase were detected at different nitrate and phosphorus concentrations. In the absence of nitrogen and phosphorus in the medium, nitrite reductase activity is the highest. This research provides theoretical guidance for optimization of culture medium for H. pluvialis and also provides an experimental basis for understanding of nitrogen metabolism pathway in H. pluvialis.

Haematococcus pluvialis is a commercial microalga, that produces abundant levels of astaxanthin under stress conditions. Acetate and Fe2+ are reported to be important for astaxanthin accumulation in H. pluvialis. In order to study the synergistic effects of high light stress and these two factors, we obtained transcriptomes for four groups: high light irradiation (HL), addition of 25 mM acetate under high light (HA), addition of 20 μM Fe2+ under high light (HF) and normal green growing cells (HG). Among the total clean reads of the four groups, 156,992 unigenes were found, of which 48.88% were annotated in at least one database (Nr, Nt, Pfam, KOG/COG, SwissProt, KEGG, GO). The statistics for DEGs (differentially expressed genes) showed that there were more than 10 thousand DEGs caused by high light and 1800–1900 DEGs caused by acetate or Fe2+. The results of DEG analysis by GO and KEGG enrichments showed that, under the high light condition, the expression of genes related to many pathways had changed, such as the pathway for carotenoid biosynthesis, fatty acid elongation, photosynthesis-antenna proteins, carbon fixation in photosynthetic organisms and so on. Addition of acetate under high light significantly promoted the expression of key genes related to the pathways for carotenoid biosynthesis and fatty acid elongation. Furthermore, acetate could obviously inhibit the expression of genes related to the pathway for photosynthesis-antenna proteins. For addition of Fe2+, the genes related to photosynthesis-antenna proteins were promoted significantly and there was no obvious change in the gene expressions related to carotenoid and fatty acid synthesis.

To optimize the cultivation media for the growth rate of Haematococcus pluvialis and to study the transcription regulation of the algal nitrate reductase (NR), a key enzyme for nitrogen metabolism.The NR gene from H. pluvialis hd7 consists of 5636 nucleotides, including 14 introns. The cDNA ORF is 2718 bp, encoding a 905 aa protein with three conserved domains. The NR amino acids of H. pluvialis hd7 are hydrophilic and have similarity of 72% compared to that of Dunaliella. NR transcription increased with an increase of nitrate concentration from 0.4 to 1 g/l. A deficiency of nitrogen increased NR transcription significantly. The transcription level of NR increased at phosphorus concentrations from 0.08 to 0.2 g/l, with a maximum at 0.08 g/l. The optimum parameters of medium component for transcription of NR and growth of H. pluvialis were 0.3 g NaNOThis study provides a better understanding of nitrate regulation in H. pluvialis.