Regulation of carotenoid biosynthetic genes expression and carotenoid accumulation in the green alga Haematococcus pluvialis under nutrient stress conditions

Abstract

Haematococcus pluvialis, a green alga, accumulates carotenoids, predominantly astaxanthin, when exposed to stress conditions. In the present work, changes in the pigment profile and expression of carotenogenic genes under various nutrient stress conditions and their regulation were studied. Nutrient stress and higher light intensity in combination with NaCl/sodium acetate (SA) enhanced total carotenoid and total astaxanthin content to 32.0 and 24.5 mg g(-1) of dry biomass, respectively. Expression of carotenogenic genes, phytoene synthase (PSY), phytoene desaturase (PDS), lycopene cyclase (LCY), beta-carotene ketolase (BKT), and beta-carotene hydroxylase (CHY) were up-regulated under all the stress conditions studied. However, the extent of expression of carotenogenic genes varied with stress conditions. Nutrient stress and high light intensity induced expression of astaxanthin biosynthetic genes, BKT and CHY, transiently. Enhanced expression of these genes was observed with SA and NaCl/SA, while expression was delayed with NaCl. The maximum content of astaxanthin recorded in cells grown in medium with SA and NaCl/SA correlated with the expression profile of the astaxanthin biosynthetic genes. Studies using various inhibitors indicated that general carotenogenesis and secondary carotenoid induction were regulated at both the transcriptional and the cytoplasmic translational levels. The induction of general carotenoid synthesis genes was independent of cytoplasmic protein synthesis while BKT gene expression was dependent on de novo protein synthesis.

Astaxanthin in microalgae: pathways, functions and biotechnological implications

“…They also induced astaxanthin synthesis independent of de novo protein synthesis (Kobayashi et al 1993, Steinbrenner andLinden 2001), suggesting ROS mediate stress response and carotenogenesis in H. pluvialis at a post-translational level (Steinbrenner and Linden 2003). Unlike PDS and CrtR-b, however, treatment with various transcriptional and translational inhibitors suggested that BKT gene expression was dependent on de novo protein synthesis (Vidhyavathi et al 2008). Considering PDS is shown to be located in the chloroplast, whereas BKT activity is found in the cytosolic LBs, this discrepancy can be explained by the distinct subcellular localization of individual carotenoid biosynthetic enzymes.…”

Astaxanthin and Related Xanthophylls

“…However, under stress conditions, β(beta)-carotene is converted into astaxanthin primarily via echinenone, canthaxanthin, and phoenicoxanthin, being β(beta)-carotene and echinenone substrates of BKT, while canthaxanthin and phoenicoxanthin are the substrates of CHY. In this way, astaxanthin accumulates as a secondary carotenoid under stress conditions [ 98 ]. Further introduction of fatty acids to the hydroxyl groups by esterifi cation leads to the production of mono-and di-esterifi ed astaxanthin in H. pluvialis [ 93 ].…”

Microbial hitchhikers on intercontinental dust: catching a lift in Chad

“…Ha. pluvialis produces astaxanthin that protects the photosynthetic apparatus from photo-oxidative damage (under high light intensities) or nutrient stresses (Vidhyavathi et al, 2008). HtS showed that members of the Ulvophyceae, Chlorophyceae, Charophyceae, Prasinophyceae, Zygnemophyceae, Bacillariophyceae and Chrysophyceae were also present, but they may have been dormant and thus not observed in culture.…”