Carotenoids Overproduction in Dunaliella Sp.: Transcriptional Changes and New Insights through Lycopene β Cyclase Regulation

Fatma Elleuch,Patrick Baril,Chantal Pichon,Mohamed Barkallah,Hajer Ben Hlima,Slim Abdelkafi,Imen Fendri

doi:10.3390/app9245389

Abstract

Dunaliella is a green microalga known for its ability to produce high levels of carotenoids under well-defined growing conditions. Molecular responses to the simultaneous effect of increasing salinity, light intensity and decrease of nitrogen availability were investigated in terms of their effect on different metabolic pathways (isoprenoids synthesis, glycolysis, carbohydrate use, etc.) by following the transcriptional regulation of enolase (ENO), 1-deoxy-D-xylulose 5-phosphate synthase (DXS), lycopene β-cyclase (LCYB), carotene globule protein (CGP), chloroplast-localized heat shock protein (HSP70), and chloroplast ribulose phosphate-3-epimerase (RPE) genes. The intracellular production of carotenoid was increased five times in stressed Dunaliella cells compared to those grown in an unstressed condition. At transcriptional levels, ENO implicated in glycolysis, and revealing about polysaccharides degradation, showed a two-stage response during the first 72 h. Genes directly involved in β-carotene accumulation, namely, CGP and LCYB, revealed the most important increase by about 54 and 10 folds, respectively. In silico sequence analysis, along with 3D modeling studies, were performed to identify possible posttranslational modifications of CGP and LCYB proteins. Our results described, for the first time, their probable regulation by sumoylation covalent attachment as well as the presence of expressed SUMO (small ubiquitin-related modifier) protein in Dunaliella sp.

Highlights

The genus Dunaliella is composed of 24 unicellular species, uninucleate [1], enclosed by a glycocalyx [2] and without a rigid polysaccharide wall, allowing a rapid response to hypo or hyperosmotic conditions [3]
A rise in salinity and light intensity was applied against a decrease in nitrogen source
The follow-up of the growth among 29 days showed that DSS maintained the same growth rate as DSC during the first 6 days of culture (Figure 1a)

Summary

Introduction

The genus Dunaliella is composed of 24 unicellular species, uninucleate [1], enclosed by a glycocalyx [2] and without a rigid polysaccharide wall, allowing a rapid response to hypo or hyperosmotic conditions [3]. The halotolerant Dunaliella salina, the holotype of this genus, is characterized by an exceptional capacity to survive under some environmental stress by producing added value compounds as glycerol, polyunsaturated fatty acids, and a high percentage of β-carotene reaching 10% to 14% of dry weight [2]. The β-carotene molecule is an orange compound, comprising a long conjugated chain of eight isoprene units with a center of symmetry and a β-cyclohexene ring at each end [5].

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Discussion

Conclusion