Browsing by Author "Henriques, Nuno"
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- Molecular and functional characterization of a cDNA encoding 4-hydroxy-3-methylbut-2-enyl diphosphate reductase from Dunaliella salinaPublication . Ramos, Ana; Marques, A. R.; Rodrigues, M.; Henriques, Nuno; Baumgartner, Alexandra; Castilho, Rita; Brenig, Bertram; Varela, J.In green algae,the final step of the plastidial methylerythritol phosphate (MEP) pathway is catalyzed by 4-hydroxy-3-methylbut-2-enyldiphosphate reductase(HDR; EC: 1.17.1.2),an enzyme proposed to play a keyrole in the regulation of isoprenoid biosynthesis. Here we report the isolation and functional characterization of a 1959- bp Dunaliella salina HDR (DsHDR) cDNA encoding a deduced polypeptide of 474 amino acid residues. Phylogenetic analysis implied a cyanobacterial origin for plant and algal HDR genes. Steady-state DsHDR transcript levels were higher in D. salina cells submitted to nutritional depletion, high salt and/or high light, suggesting that DsHDR may respond to the same environmental cues as genes involved in carotenoid biosynthesis.
- Nutrient limitation is the main regulatory factor for carotenoid accumulation and for Psy and Pds steady state transcript levels in Dunaliella salina (Chlorophyta) exposed to high light and salt stressPublication . Coesel, Sacha; Baumgartner, Alexandra; Teles, Lícia; Ramos, Ana; Henriques, Nuno; Cancela, Leonor; Varela, J.Dunaliella salina (Dunal) Teodoresco (1905) is a green unicellular alga able to withstand severe salt, light, and nutrient stress, adaptations necessary to grow in harsh environments such as salt ponds. In response to such growth conditions, this microalga accumulates high amounts of β-carotene in its single chloroplast. In this study, we show that carotenoid accumulation is consistently inhibited in cells grown in nutrient-supplemented media and exposed either to high-light or medium-low-light conditions. Likewise, carotenogenesis in cells shifted to higher salinity (up to 27% NaCl) under medium-low-light conditions is inhibited by the presence of nutrients. The steady-state levels of transcripts encoding phytoene syn- thase and phytoene desaturase increased substantially in D. salina cells shifted to high light or high salt under nutrient- limiting conditions, whereas the presence of nutrients inhibited this response. The regulatory effect of nutrient availability on the accumulation of carotenoids and mes- senger RNA levels of the first two enzymes committed to carotenoid biosynthesis is discussed.