Carotenoid genes transcriptional regulation for astaxanthin accumulation in fresh water unicellular alga Haematococcus pluvialis by gibberellin A3 (GA3).

The fresh water unicellular alga Haematococcus pluvialis is a promising natural source of astaxanthin. The present study investigated the transcriptional expression of carotenoid genes for astaxanthin accumulation in H. pluvialis using real-time fluorescence quantitative PCR (qRT-PCR). With treatments of 20 and 40 mg/L of gibberllin A3 (GA3), five genes ipi-1, ipi-2, psy, pds and bkt2 were up-regulated with different expression profiles. GA20 (20 mg/L of GA3) treatment had a greater effect on transcriptional expression of bkt2 than on ipi-1 ipi-2, psy and pds (>4-fold up-regulation). However, GA40 (40 mg/L of GA3) induced more transcriptional expression of ipi-2, psy and bkt2 than both ipi-1 and pds. The expression of lyc, crtR-B and crtO for astaxanthin biosynthesis was not affected by GA3 in H. piuvialis. In the presence of GA3, astaxanthin biosynthesis genes of ipi-1, pds and bkt2 were up-regulated at transcriptional level, psy at post-transcriptional level, whereas ipi-2 was up-regulated at both levels. The study could potentially lead to a scale application of exogenous GA3 in astaxanthin production with H. pluvialis just like GAs perform in increasing crops production and it would provide new insight about the multifunctional roles of carotenogenesis in response to GA3.

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.

Daucus carota as a novel model to evaluate the effect of light on carotenogenic gene expression

Carotenoids are synthesized in prokaryotic and eukaryotic organisms. In plants and algae, these lipophilic molecules possess antioxidant properties acting as reactive oxygen species scavengers and exert functional roles in hormone synthesis, photosynthesis, photomorphogenesis and in photoprotection. During the past decade almost all carotenogenic genes have been identified as a result of molecular, genetic and biochemical approaches utilizing Arabidopsis thaliana as the model system. Studies carried out in leaves and fruits of A. thaliana and tomato determined that light regulates carotenoid biosynthesis preferentially through the modulation of carotenogenic gene transcription. In this work we showed for the first time that light induces accumulation of psy 1, pds and zds2 transcripts in leaves of Daucus carota (carrot), a novel plant model. In addition, modified roots of carrots exposed to light accumulate zdsl, whereas the pds gene is highly repressed, suggesting that some carotenogenic genes, which are expressed in roots, are regulated by light. Additionally, light negatively regulates the development of the modified carrot root in a reversible manner. Therefore, this suggests that light affects normal growth and carotenogenic gene expression in the modified root of carrot plants. The molecular insight gained into the light-regulated expression of carotenoid genes in this and other model systems will facilitate our understanding of the regulation of carotenoid biosynthesis to improve the prospects for the metabolic engineering of carotenoid production in plants.

Expression of the carotenoid biosynthesis genes in Xanthophyllomyces dendrorhous

In the yeast Xanthophyllomyces dendrorhous the genes idi, crtE, crtYB, crtl and ast are involved in the biosynthesis of astaxanthin from isopentenyl pyrophosphate. The carotenoid production and the kinetics of mRNA expression of structural genes controlling the carotenogenesis in a wild-type ATCC 24230 and in carotenoid overproducer deregulated atxS2 strains were studied. The biosynthesis of carotenoid was induced at the late exponential growth phase in both strains. However, the cellular carotenoid concentration was four times higher in atxS2 than in the wild-type strain in the exponential growth phase, suggesting that carotenogenesis was deregulated in atxS2 at the beginning of growth. In addition, the maximum expression of the carotenogenesis genes at the mRNA level was observed during the induction period of carotenoid biosynthesis in the wild-type strain. The mRNA level of the crtYB, crtl, ast genes and to a lesser extent the idi gene, decayed at the end of the exponential growth phase. The mRNA levels of the crtE gene remained high along the whole growth curve of the yeast. In the atxS2 strain the mRNA levels of crtE gene were about two times higher than the wild-type strain in the early phase of the growth cycle.