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

Abstract

The carotenoid biosynthesis pathway catalyses the synthesis of essential pigments that are crucial for light harvesting and photoprotection in photosynthetic organisms. It allows the production of several commercially important compounds and is the target of many herbicides. In the present work we studied the influence of light on the carotenoid composition and the expression of genes encoding the main steps of the pathway in the freshwater microalga Chlamydomonas reinhardtii. We observed that there is an activation of the xanthophyll cycle in response to high light, but also in response to other stress conditions, such as nitrogen starvation, which has not been reported previously. We analysed the expression level of (1) genes encoding the two first enzymes of the pathway, phytoene synthase and phytoene desaturase; (2) the enzymes responsible for the cyclization of lycopene, lycopene -cyclase and lycopene "-cyclase; (3) zeaxanthin epoxidase, which catalyses the epoxidation of zeaxanthin; and (4) the three known carotene hydroxylases, directly involved in the synthesis of xanthophylls from and -carotene. Measurements of carotenoid content in the presence of inhibitors of protein and carotenoid synthesis suggest that only one of the two possible routes for the synthesis of zeaxanthin upon transference to high light, either the de novo synthesis of carotenoids or the interconversion of violaxanthin and zeaxanthin, is dependent on protein synthesis. The high increase in the transcript levels of the cytochrome-dependent carotene -and "-hydroxylases in response to high light suggests an important role of these enzymes in regulation of xanthophyll synthesis upon light stress. These conclusions may be of high interest if efficient engineering of the pathway is to be accomplished.

Characterization of cell growth and starch production in the marine green microalga Tetraselmis subcordiformis under extracellular phosphorus-deprived and sequentially phosphorus-replete conditions

“…3b). This may be attributed to the synthesis of xanthophylls under stressful conditions that contribute to the activation of the xanthophyll cycle to dissipate surplus absorbed light energy as heat, rendering the microalgae less prone to photo-oxidative damage (Couso et al 2012;Wykoff et al 1998). Our results also show that the Car/Chl ratio is positively related to starch content and inversely related to F v /F m (Figs.…”

Isolation and Characterization of a Marine Microalga for Biofuel Production with Astaxanthin as a Co-Product

“…In the red stage, cells were wrinkled, and the cell wall was abridged (Figure 2b). It has been reported that the synthesis of carotenoids was subject to detrimental conditions, such as high light intensity, nutrient starvation or other stress conditions [20]. Thus, it was inferred that the red cell might have been under stress.…”

“…In order to estimate the growth of microalgae, the dry cell weight (DCW) was measured according to Couso et al [20]. Microalgae were cultured to the log phase of growth in flasks, then 50 mL cell cultures were transferred to glass columns (4.1 cm in diameter, 37 cm in height), and diluted with 250 mL of F medium with different concentrations of NaNO 3 (0.075, 0.15, 0.3, 0.6 and 0.9 g/L) to ensure the OD 680 of initial culture was approximate 0.2.…”

Isolation and characterization of pigment deficient insertional mutants in the chlorophyte Chlamydomonas reinhardtii

“…In Chlamydomonas this response to high light shifts is well documented [4]. The synthesis of zeaxanthin in Chlamydomonas cells after exposure to a high light stress [35] and other kind of stress conditions [36] has been previously reported. It has been demonstrated that this zeaxanthin is produced from violaxanthin via the xanthophyll cycle [33], but neither the enzyme nor the gene encoding this putative violaxanthin de-epoxidase (VDE) has been identified yet in Chlamydomonas.…”