Zhengquan Gao

Saccharina genomes provide novel insight into kelp biology.

Seaweeds are essential for marine ecosystems and have immense economic value. Here we present a comprehensive analysis of the draft genome of Saccharina japonica, one of the most economically important seaweeds. The 537-Mb assembled genomic sequence covered 98.5% of the estimated genome, and 18,733 protein-coding genes are predicted and annotated. Gene families related to cell wall synthesis, halogen concentration, development and defence systems were expanded. Functional diversification of the mannuronan C-5-epimerase and haloperoxidase gene families provides insight into the evolutionary adaptation of polysaccharide biosynthesis and iodine antioxidation. Additional sequencing of seven cultivars and nine wild individuals reveal that the genetic diversity within wild populations is greater than among cultivars. All of the cultivars are descendants of a wild S. japonica accession showing limited admixture with S. longissima. This study represents an important advance toward improving yields and economic traits in Saccharina and provides an invaluable resource for plant genome studies.

Induction of salicylic acid (SA) on transcriptional expression of eight carotenoid genes and astaxanthin accumulation in Haematococcus pluvialis

The green alga Haematococcus pluvialis can produce large amounts of pink carotenoid astaxanthin which is a high value ketocarotenoid. In our study, transcriptional expression patterns of eight carotenoid genes in H. pluvialis in response to SA were measured using qRT-PCR. Results indicated that both 25 and 50 mg/L salicylic acid (SA) could increase astaxanthin productivity and enhance transcriptional expression of eight carotenoid genes in H. pluvialis. But these genes exhibited different expression profiles. Moreover, SA25 (25 mg/L SA) induction had a greater effect on the transcriptional expression of ipi-1, psy, pds, crtR-B and lyc (more than 6-fold up-regulation) than on ipi-2, bkt and crtO, but SA50 (50 mg/L SA) treatment had a greater impact on the transcriptional expression of ipi-1, ipi-2, pds, crtR-B and lyc than on psy, bkt and crtO. Furthermore, astaxanthin biosynthesis under SA was up-regulated mainly by ipi-1, ipi-2, psy, crtR-B, bkt and crtO at transcriptional level, lyc at post-transcriptional level and pds at both levels. Summarily, these results suggest that SA constitute molecular signals in the network of astaxanthin biosynthesis. Induction of astaxanthin accumulation by SA without any other stimuli presents an attractive application potential in astaxanthin production with H. pluvialis.

Differential Expression of Carotenogenic Genes, Associated Changes on Astaxanthin Production and Photosynthesis Features Induced by JA in H. pluvialis

Haematococcus pluvialis is an organism that under certain conditions can produce astaxanthin, an economically important carotenoid. In this study, the transcriptional expression patterns of eight carotenogenic genes of H. pluvialis in response to jasmonic acid (JA) were evaluated using real-time PCR. Astaxanthin accumulation action and photosynthesis flourescence were monitored at the same time. The results showed all eight genes exhibited higher transcriptional expression significantly under JA treatments. JA25 (25 mg/L) induction had greater effect (>10-fold up-regulation) on the transcriptional expression of pds, crtR-B and lyc than on ipi-1, ipi-2, psy, bkt2, and crtO. JA50 (50 mg/L) treatment had greater impact on the transcriptional expression of ipi-1, ipi-2, psy, crtR-B and crtO than on pds, lyc and bkt2. Astaxanthin biosynthesis in the presence of JA appeared to be up-regulated mainly by psy, pds, crtR-B, lyc, bkt2 and crtO at the transcriptional level and ipi-1, ipi-2 at both transcriptional and post-transcriptional levels. Under JA induction, the photosynthetic efficiency [Y (II)] and the maximum quantum efficiency of PS II (Fv/Fm) decreased significantly, but the non-photochemical quenching of chlorophyll fluorescence (NPQ) increased drastically with the accumulation of astaxanthin.

Detection and quantitation of lipid in the microalga Tetraselmis subcordiformis (Wille) Butcher with BODIPY 505/515 staining.

BODIPY 505/515, a lipophilic bright green fluorescent dye was tested for lipid detection in the microalga Tetraselmis subcordiformis. A concentration of 0.28 μg ml(-1) and staining for 6 min was optimal. Lipid bodies stained with BODIPY505/515 had a characteristic green fluorescence. Their volumes were determined using the sphere volume formula. Lipid accumulation under different nitrogen concentrations was analyzed. With an increase in NaNO(3) concentration from 0 to 240 mg L(-1), the maximum algal concentration increased from 8.23 ± 0.62 (× 10(5) cells ml(-1)) to 1.61 ± 0.13 (×10(6) cells ml(-1)), while the maximum volume of intracellular neutral lipid decreased from 9.78 ± 1.77 μm(3) cell(-1) to 6.00 ± 0.59 μm(3) cell(-1). A comparison of the lipid contents measured by BODIPY 505/515 staining and the gravimetric method showed a positive correlation coefficient of R(2) = 0.93. BODIPY 505/515 staining is a promising method in lipid quantitation in T. subcordiformis.

Evaluation of the potential role of the macroalga Laminaria japonica for alleviating coastal eutrophication.

The rapid development of human activities has caused serious eutrophication of coastal waters in China in the recent decades. The study of the biofiltration capacity of Laminaria japonica under laboratory conditions showed a significant nutrient uptake. After 36 h of incubation, around 42%, 46%, 44% of N and 45%, 42%, 35% of P were removed from three gradients of medium concentrations, respectively. In the conditions of different ratios of N/P and NO(3)-N/NH(4)-N, the optimum N/P ratio for nutrient uptake was 7.4 and L. japonica preferred NO(3)-N rather than NH(4)-N as nitrogen source. Temperature and irradiance affected uptake rates significantly. The maximal N uptake rate appeared at 10°C and 18 μmol photons m(-2)s(-1) and the maximal P uptake rate was found at 15°C and 144 μmol photons m(-2)s(-1). Moreover, further studies were needed to investigate the bioremediation potential of L. japonica in the open sea.

Analysis of mRNA expression profiles of carotenogenesis and astaxanthin production of Haematococcus pluvialis under exogenous 2, 4-epibrassinolide (EBR).

The fresh-water green unicellular alga Haematococcus pluvialis is known to accumulate astaxanthin under stress conditions. In the present study, transcriptional expression of eight genes involved in astaxanthin biosynthesis exposed to EBR (25 and 50 mg/L) was analyzed using qRT-PCR. The results demonstrated that both 25 and 50 mg/L EBR could increase astaxanthin productivity and the eight carotenogenic genes were up-regulated by EBR with different expression profiles. Moreover, EBR25 induction had a greater influence on the transcriptional expression of ipi-1, ipi-2, crtR-B, lyc and crtO (> 5- fold up-regulation) than on psy, pds, bkt; EBR50 treatment had a greater effect on the transcriptional expression of ipi-2, pds, lyc, crtR-B, bkt and crtO than on ipi-1 and psy. Furthermore, astaxanthin biosynthesis under EBR was up-regulated mainly by ipi1־ and psy at the post-transcriptional level, pds, lyc, crtR-B, bkt and crtO at the transcriptional level and ipi-2 at both levels.

Allelopathic Interactions between the Opportunistic Species Ulva prolifera and the Native Macroalga Gracilaria lichvoides

Allelopathy, one type of direct plant competition, can be a potent mechanism through which plant communities are structured. The aim of this study was to determine whether allelopathic interactions occur between the opportunistic green tide-forming species Ulva prolifera and the native macroalga Gracilaria lichvoides, both of which were collected from the coastline of East China sea. In laboratory experiments, the presence of G. lichvoides at 1.25 g wet weight L−1 significantly inhibited growth and photosynthesis of U. prolifera at concentrations of 1.25, 2.50, and 3.75 g wet weight L−1 (p<0.05) in both semi-continuous co-culture assays and in co-culture assays without nutrient supplementation. In contrast, although U. prolifera had a density effect on G. lichvoides, the differences among treatments were not significant (p>0.05). Culture medium experiments further confirmed that some allelochemicals may be released by both of the tested macroalgae, and these could account for the observed physiological inhibition of growth and photosynthesis. Moreover, the native macroalgae G. lichvoides was a stronger competitor than the opportunistic species U. prolifera. Collectively, the results of the present study represent a significant advance in exploring ecological questions about the effects of green tide blooms on the macroalgal community.

Transcriptome Analysis in Haematococcus pluvialis: Astaxanthin Induction by Salicylic Acid (SA) and Jasmonic Acid (JA)

Haematococcus pluvialis is an astaxanthin-rich microalga that can increase its astaxanthin production by salicylic acid (SA) or jasmonic acid (JA) induction. The genetic transcriptome details of astaxanthin biosynthesis were analyzed by exposing the algal cells to 25 mg/L of SA and JA for 1, 6 and 24 hours, plus to the control (no stress). Based on the RNA-seq analysis, 56,077 unigenes (51.7%) were identified with functions in response to the hormone stress. The top five identified subcategories were cell, cellular process, intracellular, catalytic activity and cytoplasm, which possessed 5600 (~9.99%), 5302 (~9.45%), 5242 (~9.35%), 4407 (~7.86%) and 4195 (~7.48%) unigenes, respectively. Furthermore, 59 unigenes were identified and assigned to 26 putative transcription factors (TFs), including 12 plant-specific TFs. They were likely associated with astaxanthin biosynthesis in Haematococcus upon SA and JA stress. In comparison, the up-regulation of differential expressed genes occurred much earlier, with higher transcript levels in the JA treatment (about 6 h later) than in the SA treatment (beyond 24 h). These results provide valuable information for directing metabolic engineering efforts to improve astaxanthin biosynthesis in H. pluvialis.

The effects of abscisic acid, salicylic acid and jasmonic acid on lipid accumulation in two freshwater Chlorella strains

Sustainable renewable energy is being hotly debated globally because the continued use of finite fossil fuels is now widely recognized as being unsustainable. Microalgae potentially offer great opportunities for resolving this challenge. Abscisic acid (ABA), jasmonic acid (JA) and salicylic acid (SA) are involved in regulating many physiological properties and have been widely used in higher plants. To test if phytohormones have an impact on accumulating lipid for microalgae, ABA, JA and SA were used to induce two Chlorella strains in the present study. The results showed 1.0 mg/L ABA, 10 mg/L SA, and 0.5 mg/L JA, led strain C. vulgaris ZF strain to produce a 45%, 42% and 49% lipid content that was 1.8-, 1.7- and 2.0-fold that of controls, respectively. For FACHB 31 (number 31 of the Freshwater Algae Culture Collection at the Institute of Hydrobiology, Chinese Academy of Sciences), the addition of 1.0 mg/L ABA, 10 mg/L SA, and 0.5 mg/L, JA produced 33%, 30% and 38% lipid content, which was 1.8-, 1.6- and 2.1-fold that of controls, respectively. As for lipid productivity, 1.0 mg/L ABA increased the lipid productivity of C. vulgaris ZF strain and FACHB-31 by 123% and 44%; 10 mg/L SA enhanced lipid productivity by 100% and 33%; the best elicitor, 0.5 mg/L JA, augmented lipid productivity by 127% and 75% compared to that of controls, respectively. The results above suggest that the three phytohormones at physiological concentrations play crucial roles in inducing lipid accumulation in Chlorella.

Characterization and production of tetraspore-derived seedlings of Grateloupia lanceolata (Halymeniales, Rhodophyta) in northeastern China

Ye N., Zhang X., Wang H., Lian W., Mao Y., Xu D., Li B., Liang C., Zou J., Zhu B., Jiang Z., Gao Z. and Li D. 2012. Characterization and production of tetraspore-derived seedlings of Grateloupia lanceolata (Halymeniales, Rhodophyta) in northeastern China. Phycologia 51: 330–339. DOI: 10.2216/11-03.1 In this study, Grateloupia lanceolata, newly recorded from northeastern China, was classified on the basis of morphology and rbcL sequence analysis and also raised in a laboratory to evaluate the feasibility of producing tetraspore-derived seedlings. Analysis of the rbcL sequence showed the samples to be monophyletic with G. lanceolata and different from any other species of the genus. Analysis of variance indicated that time has a significant (P < 0.01) effect on both tetraspore output and the percentage of total tetraspores released; those released in the first 2 d made up more than 72% of the total sporulation output; whereas, those released in the last 2 d contributed only 2.52%. In culture, tetraspores released from the unilocular sporangia developed into small discs in one week, and 87% ± 5.7% of the tetraspores that settled developed into sporelings after 9 wk of culture. Tetraspore culture of G. lanceolata in tanks and in the open sea proved to be a feasible method of generating large numbers of individual gametophytes economically.