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De novo transcriptomic profiling of halotolerant microalga Dunaliella salina (Chlorophyta) in response to reciprocal alteration of salinities.

ABSTRACT: The unicellular microalga Dunaliella salina is one of the halotolerant and cell wall-less green microalgae in Dunaliella genus. The ability of halotolerance in Dunaliella is attributed to the accumulation of glycerol. Both sugar made by photosynthesis and starch serve as carbon sources for glycerol biosynthesis. Quantitative PCR-based analyses concluded no apparent transcriptional regulation of glycerol, carbon fixation, and starch metabolisms upon salinity stresses. To examine whether or not transcriptional regulation is involved at the transcriptomic level, we assembled a de novo deep sequencing transcriptome. By using a pathway-based approach, we show that low- and high-salt (i.e., 0.5M versus 2M NaCl) adapted cells share a common transcriptomic profile and that subsets of ESTs associated with energy metabolisms are less affected upon salinity stress. We find that enzymes involved in glycerol, carbon fixation, and starch metabolisms are encoded by multiple EST isoforms. We show that EST isoforms encoding dihydroacetone reductase in glycerol metabolism, phosphoglycerate kinase in carbon fixation, and beta-amylase and fructobiphosphate aldolase in starch metabolism display a correlated transcriptional level change to the alteration of glycerol and starch contents upon salinity stresses. Taken together, our results demonstrate that some enzymes involved in glycerol, carbon fixation, and starch metabolisms are regulated at the transcriptional level upon salinity stresses. Furthermore, our analyses indicate that energy metabolisms are not drastically affected upon salinity stresses, consistent with its ability to adapt to a wide range of salinities.

ORGANISM(S): Dunaliella salina

PROVIDER: GSE74466 | GEO | 2017/02/22

REPOSITORIES: GEO

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Project description:Algae of the genus Dunaliella are known to be able to grow in a wide range of salinities. To investigate which genes may be important for growth under extremely low or high salinities, a survey of the Dunaliella sp. transcriptome was performed by microarray analysis. For the cDNA microarray 778 expressed sequence tags (ESTs) were generated from a cDNA library of Dunaliella sp. The cDNA microarray was used to compare the transcription profile of cells that were acclimated to extreme saline conditions (0.08 M and 4.5 M NaCl) with the transcription profile of cells acclimated to an intermediate salinity at 1.5 M NaCl. The comparative microarray analysis indicated that 211 out of the 778 ESTs differed in their expression levels more than two-fold in cells grown at extreme different salinity when compared to cells grown at intermediate salinity (1.5M NaCl). The sequences of these 211 cDNAs were classified into 169 non-redundant gene clusters. Of these genes, the expression of 36 genes was increased and 69 genes were suppressed in cells grown at low salinity. The expression of 49 genes was increased and 85 genes were suppressed in cells grown at high salinity. One-hundred thirty four genes have been revealed to show up- and down-regulation by high salinity (4.5M NaCl). Of the high salinity-regulated genes 52% were also influenced by low salinity (0.08M NaCl), revealing a dense overlap between low and high salt responses. Only 35 genes are regulated independently by low salt condition. Strong relationships, however, were observed in the expression of these extreme salinity-responsive genes based on Venn diagram analysis, which found 70 genes that responded to these two salinity conditions. Refined expression analysis using gene-specific primers and real-time PCR for selected transcripts was in agreement with microarray results for most genes tested. This study provides the first large-scale survey of the transcriptome in the microalga Dunaliella sp. and it provides a platform for further functional investigation of differentially expressed genes in Dunaliella. Keywords: Low salt(0.08M NaCl) or high salt(4.5M NaCl)-acclimated cells

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De novo transcriptomic profiling of halotolerant microalga Dunaliella salina (Chlorophyta) in response to reciprocal alteration of salinities.

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