Abstract
The unicellular alga Dunaliella bardawil is a highly salt-tolerant organism, capable of accumulating glycerol, glycine betaine and β-carotene under salt stress, and has been considered as an excellent model organism to investigate the molecular mechanisms of salt stress responses. In this study, several carotenogenic genes (DbCRTISO, DbZISO, DbLycE and DbChyB), DbBADH genes involved in glycine betaine synthesis and genes encoding probable WRKY transcription factors from D. bardawil were isolated, and promoters of DbCRTISO and DbChyB were cloned. The promoters of DbPSY, DbLycB, DbGGPS, DbCRTISO and DbChyB contained the salt-regulated element (SRE), GT1GMSCAM4, while the DbGGPS promoter has another SRE, DRECRTCOREAT. All promoters of the carotenogenic genes had light-regulated elements and W-box cis-acting elements. Most WRKY transcription factors can bind to the W-box, and play roles in abiotic stress. qRT-PCR analysis showed that salt stress up-regulated both carotenogenic genes and WRKY transcription factors. In contrast, the transcription levels of DbBADH showed minor changes. In D. bardawil, it appears that carotenoid over-accumulation allows for the long-term adaptation to salt stress, while the rapid modulation of glycine betaine biosynthesis provides an initial response.
Highlights
The unicellular alga Dunaliella bardawil is a highly salt-tolerant organism, capable of accumulating glycerol, glycine betaine and β-carotene under salt stress, and has been considered as an excellent model organism to investigate the molecular mechanisms of salt stress responses
After PCR amplification, subcloning and sequencing, we found that the coding sequences (CDS) of the genes of interest from D. bardawil FACHB-847 were 100% identical to those from D. tertiolecta UTEX LB 999
In our research group, genes such as geranylgeranyl pyrophosphate synthase (GGPS), phytoene synthase (PSY), phytoene desaturases (PDS), ZDS and LycB have been isolated from D. bardawil FACHB-8473,15,18
Summary
The unicellular alga Dunaliella bardawil is a highly salt-tolerant organism, capable of accumulating glycerol, glycine betaine and β-carotene under salt stress, and has been considered as an excellent model organism to investigate the molecular mechanisms of salt stress responses. In D. bardawil, it appears that carotenoid over-accumulation allows for the long-term adaptation to salt stress, while the rapid modulation of glycine betaine biosynthesis provides an initial response. The long-term response mechanisms, including salt-induced genes expression, salt tolerance related proteins or transcription factors, allow D. bardawil cells to acclimate to high salinity[2]. Glycine betaine can be accumulated during stress response in many crop plants, including sugarbeet, spinach, barley, wheat and sorghum. Changes in multiple biological process (such as protein synthesis, membrane stabilization, signal transduction, and redox energy production) in response to salt stress suggested that more than one mechanism may play a role in the unique capacity of salt tolerance of Dunaliella cells[2]
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