title: Hypoosmotic expression of Dunaliella bardawil ζ-carotene desaturase is attributed to a hypoosmolarity-responsive element different from other key carotenogenic genes.
abstract: Some key carotenogenic genes (crts) in Dunaliella bardawil are regulated in response to salt stress partly due to salt-inducible cis-acting elements in their promoters. Thus, we isolated and compared the ζ-carotene desaturase (Dbzds) promoter with other crts promoters including phytoene synthase (Dbpsy), phytoene desaturase (Dbpds), and lycopene β-cyclase1 (DblycB1) to identify salt-inducible element(s) in the Dbzds promoter. In silico analysis of the Dbzds promoter found several potential cis-acting elements, such as abscisic acid response element-like sequence, myelocytomatosis oncogene1 recognition motif, AGC box, anaerobic motif2, and activation sequence factor1 binding site. Remarkably, instead of salt-inducible elements, we found a unique regulatory sequence architecture in the Dbzds promoter: a hypoosmolarity-responsive element (HRE) candidate followed by a potential hypoosmolarity-inducible factor GBF5 binding site. Deletion experiments demonstrated that only HRE, but not the GBF5 binding site, is responsible for hypoosmotic expression of the fusion of Zeocin resistance gene (ble) to the enhanced green fluorescent protein (egfp) chimeric gene under salt stress. Dbzds transcripts were in accordance with those of ble-egfp driven by the wild-type Dbzds promoter. Consequently, Dbzds is hypoosmotically regulated by its promoter, and HRE is responsible for this hypoosmotic response. Finally, the hypoosmolarity mechanism of Dbzds was studied by comparing transcript profiles and regulatory elements of Dbzds with those of Dbpsy, Dbpds, DblycB1, and DblycB2, revealing that different induction characteristics of crts may correlate with regulatory sequence architecture.
authors.affiliation: College of Food Science and Engineering, South China University of Technology, Guangzhou 510640, China.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lao
authors.forename: Lan
authors.initials: L
authors.lastname: Xiao
authors.forename: Li-Xin
authors.initials: LX
authors.lastname: Luo
authors.forename: Jian-Guo
authors.initials: JG
authors.lastname: Jiang
mesh_terms: D001483:Base Sequence; D053898:Biosynthetic Pathways / Q000235:genetics; D002338:Carotenoids / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D000460:Chlorophyta / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism; D009994:Osmolar Concentration; D009995:Osmosis; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics*; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics
chemical_list: D009566:Nitrates; D010940:Plant Proteins; D012333:RNA, Messenger; D002338:Carotenoids; D012965:Sodium Chloride; D010088:Oxidoreductases; C099215:zeta-carotene desaturase