Phytoene Desaturase Is Localized Exclusively in the Chloroplast and Up-Regulated at the mRNA Level during Accumulation of Secondary Carotenoids in Haematococcus pluvialis (Volvocales, Chlorophyceae),

Abstract

The unicellular green alga Haematococcus pluvialis Flotow is known for its massive accumulation of ketocarotenoids under various stress conditions. Therefore, this microalga is one of the favored organisms for biotechnological production of these antioxidative compounds. Astaxanthin makes up the main part of the secondary carotenoids and is accumulated mostly in an esterified form in extraplastidic lipid vesicles. We have studied phytoene desaturase, an early enzyme of the carotenoid biosynthetic pathway. The increase in the phytoene desaturase protein levels that occurs following induction is accompanied by a corresponding increase of its mRNA during the accumulation period, indicating that phytoene desaturase is regulated at the mRNA level. We also investigated the localization of the enzyme by western-blot analysis of cell fractions and by immunogold labeling of ultrathin sections for electron microscopy. In spite of the fact that secondary carotenoids accumulate outside the chloroplast, no extra pathway specific for secondary carotenoid biosynthesis in H. pluvialis was found, at least at this early stage in the biosynthesis. A transport process of carotenoids from the site of biosynthesis (chloroplast) to the site of accumulation (cytoplasmatic located lipid vesicles) is implicated.

Astaxanthin in microalgae: pathways, functions and biotechnological implications

“…Immuno-localization study indicated that BKTs were localized in both the chloroplast and cytosolic LBs in H. pluvialis, although ketolase activity was detected only in the cytosolic LB preparation (Grünewald et al 2001). Since PDS is an early enzyme in the pathway that is located exclusively in the chloroplast (Grunewald et al 2000), it was proposed that transport of carotenoid precursors from the chloroplast to cytosolic LBs by a yet unknown enzymatic activity of converting zeaxanthin to astaxanthin via adonixanthin (Huang et al 2006b). When the BKT inhibitor diphenylamine was applied, C. zofingiensis accumulated zeaxanthin while H. pluvialis accumulated β-carotene , suggesting that C. zofingiensis synthesizes astaxanthin through zeaxanthin (Fig.…”

“…The PDS and two PTOX genes (i.e., PTOX1 and PTOX2) have been cloned and characterized in H. pluvialis (Grunewald et al 2000, Wang et al 2009, Li et al 2010. High light illumination and nitrogen deprivation increase the transcripts of PDS and PTOX simultaneously in H. pluvialis, suggesting that PDS and PTOX may act in concert to dehydrogenate phytoene and remove excess electrons under stress, thereby preventing over-reduction of the photosynthetic electron transport chain and the formation of excess ROS (Grunewald et al 2000, Wang et al 2009, Li et al 2010. Western-blot and immunogold labeling experiments showed that PDS is located exclusively in the chloroplast in H. pluvialis (Grunewald et al 2000).…”

Transformation of the Green Alga Haematococcus pluvialis with a Phytoene Desaturase for Accelerated Astaxanthin Biosynthesis

“…The limited sequence information that is available includes information for most of the carotenoid biosynthesis genes (12,17,21,23,37,39,40). One of these genes, the phytoene desaturase (Pds) gene, is the target for the bleaching herbicide norflurazon (5,8,25,33).…”

Assimilation of various organic carbon sources by Haematococcus strains

“…Grünewald et al (2000) showed that light is necessary for astaxanthin production. However, Haematococcus pluvialis has the ability to grow under heterotrophic conditions in the presence of sodium acetate even in darkness, though under such conditions only small quantities of astaxanthin are produced, mainly as monoesters (Zhang et al, 1999).…”