Coordinated Regulation of Gene Expression for Carotenoid Metabolism in Chlamydomonas reinhardtii

Abstract

Carotenoids are important plant pigments for both light harvesting and photooxidation protection. Using the model system of the unicellular green alga Chlamydomonas reinhardtii, we characterized the regulation of gene expression for carotenoid metabolism by quantifying changes in the transcript abundance of dxs, dxr and ipi in the plastidic methylerythritol phosphate pathway and of ggps, psy, pds, lcyb and bchy, directly involved in carotenoid metabolism, under different photoperiod, light and metabolite treatments. The expression of these genes fluctuated with light/dark shifting. Light treatment also promoted the accumulation of transcripts of all these genes. Of the genes studied, dxs, ggps and lcyb displayed the typical circadian pattern by retaining a rhythmic fluctuation of transcript abundance under both constant light and constant dark entrainments. The expression of these genes could also be regulated by metabolic intermediates. For example, ggps was significantly suppressed by a geranylgeranyl pyrophosphate supplement and ipi was upregulated by isopentenyl pyrophosphate. Furthermore, CrOr, a C. reinhardtii homolog of the recently characterized Or gene that accounts for carotenoid accumulation, also showed co-expression with carotenoid biosynthetic genes such as pds and lcyb. Our data suggest a coordinated regulation on carotenoid metabolism in C. reinhardtii at the transcriptional level.

Metabolite Profiling and Integrative Modeling Reveal Metabolic Constraints for Carbon Partitioning under Nitrogen Starvation in the Green Algae Haematococcus pluvialis

“…Similarly, high expression levels of enzymes involved in the synthesis of terpenoids were also found in Neochloris oleoabundans, under nitrogen deficiency (55). In Chlamydomonas reinhardtii, light treatment was found to promote the accumulation of all transcripts of the methylerythritol phosphate pathway (56). Specifically in the current work, the fact that astaxanthin is accumulating to a level that is 30 times higher than the initial level of total carotenoids (Fig.…”

The P450‐type carotene hydroxylase PuCHY1 from Porphyra suggests the evolution of carotenoid metabolism in red algae

“…Reverse transcription and 3′‐ and 5′‐RACE were conducted using the SMART RACE cDNA Amplification Kit (Clontech, Mountain View, CA, USA) according to the manufacturer's instructions. High‐fidelity PrimeStar DNA polymerase (Takara, Dalian, China) was used throughout this study unless specifically described, and dimethylsulfoxide (DMSO) was added to the PCR system to a final concentration of 5% (v/v) to overcome the high GC content of the templates (Sun et al ). All primers used in this study are listed in Table .…”

“…The threshold cycle (CT) values were determined using TP800 software (Takara). The expression values were calculated according to the 2 −ΔCT method (Sun et al ).…”

Synthesis of carotenoids and regulation of the carotenoid biosynthesis pathway in response to high light stress in the unicellular microalga Chlamydomonas reinhardtii

“…The few reports that have focused on the molecular response of carotenogenic pathway to light, either by qPCR or northern-blot analysis, have studied only a limited subset of genes. Bohne & Linden (2002), and more recently Sun et al (2010), studied psy and pds expression when transferring dark-or low-light-grown Chlamydomonas cells to moderate (200 mE m À2 s À1 ) white or blue light. They observed a transient induction of psy and pds expression, reaching a maximum increase 1-2 h after transfer to light and recovery of the original levels after 4 h. Similar up-regulation was observed when cells were exposed to very low intensity light (0.01 mE m À2 s À1 ) (Lohr et al, 2005;Im et al, 2006) after a dark period.…”