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 cisacting elements in their promoters. Thus, we isolated and compared the z-carotene desaturase (Dbzds) promoter with other crts promoters including phytoene synthase (Dbpsy), phytoene desaturase (Dbpds), and lycopene b-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.Carotenoids are a structurally diverse class of isoprenoids synthesized by all photosynthetic organisms and many nonphotosynthetic organisms, such as certain species of bacteria, fungi, and archaea (Goodwin, 1980). They possess many advantageous properties for the human body on account of their vitamin A activity as essential nutrients (Farré et al., 2010), prevention and treatment functions against several kinds of diseases as health care products (Michaud et al., 2000;Landrum and Bone, 2001;Shaish et al., 2006), as well as industrial agents as colorants, forages, and cosmetics (SchmidtDannert, 2000). Therefore, the investigation of biosynthetic mechanisms and commercial exploitation of carotenoids have gained increasing attraction in many laboratories and companies. Recently, at least 700 carotenoids have been characterized from natural carotenoid biosynthetic pathways (Feltl et al., 2005).Some carotenogenic microorganisms have been commercially employed to produce important carotenoids (Johnson et al., 1995;Raja et al., 2007). Among these microorganisms, the Dunaliella genus, especially Dunaliella salina and Dunaliella bardawil, has been researched extensively and exploited as a natural source of carotenoids due to its striking ability to accumulate carotenoids under certain circumstances (Amotz et al., 1982), including high light intensity, high sa...

The salt‐regulated element in the promoter of lycopene β‐cyclase gene confers a salt regulatory pattern in carotenogenesis of Dunaliella bardawil

“…There were several TATA and CAAT boxes that are typical in eukaryotic promoters, multiple light response elements (GATABOX, CGCGBOXAT and SORLIP1AT), ASF1MOTIFCAMV involved in abiotic and biotic stress, and SRE (GT1GMSCAM4). Previously, cis ‐acting elements of the promoters of Dbpsy (Lao et al ., ) and Dbzds (Lao et al ., ) have been analyzed (Table ). Dbpsy and Dblcyb promoters contained the same SRE, named GT1GMSCAM4.…”

“…It was found that the transcription levsls of some carotenogenic genes in D. bardawil were up‐regulated under salt stress (Lao et al ., ). It was shown that the Dbpsy promoter contained a salt‐regulated element (SRE) and light‐regulated elements involved in stress‐responsive gene expression (Lao et al ., ), and the Dbzds promoter had a hypoosmolarity‐responsive element (HRE) instead of salt‐inducible elements (Lao et al ., ).…”

“…In this study, we mainly studied on the cis ‐acting elements in the carotenogenic genes promoter regions under salt stress. Previously, we have analyzed the cis ‐acting elements in the promoters of some carotenogenic genes [such as Dbpsy (Lao et al ., ) and Dbzds (Lao et al ., )] involved in the carotenoid biosynthesis of D. bardawil . It was found that the transcription levsls of some carotenogenic genes in D. bardawil were up‐regulated under salt stress (Lao et al ., ).…”

“…Previously, we have analyzed the cis ‐acting elements in the promoters of some carotenogenic genes [such as Dbpsy (Lao et al ., ) and Dbzds (Lao et al ., )] involved in the carotenoid biosynthesis of D. bardawil . It was found that the transcription levsls of some carotenogenic genes in D. bardawil were up‐regulated under salt stress (Lao et al ., ). It was shown that the Dbpsy promoter contained a salt‐regulated element (SRE) and light‐regulated elements involved in stress‐responsive gene expression (Lao et al ., ), and the Dbzds promoter had a hypoosmolarity‐responsive element (HRE) instead of salt‐inducible elements (Lao et al ., ).…”

Synthesis and Function of Apocarotenoid Signals in Plants

“…The nature of the environmental and developmental stimuli that alter apocarotenoid formation may in some cases also reflect the ecological roles of apocarotenoids (e.g., as pollinator attractants). Examples of stimuli that affect apocarotenoid formation are summarized in Table I. Environmental and developmental stimuli also alter the expression of many carotenoid biosynthetic genes, altering carotenoid composition, which may in turn promote production of specific apocarotenoids [101][102][103]. However, the relationship between carotenoid and apocarotenoid levels is not always straightforward as expression and localization of substrates and enzymes will affect apocarotenoid production.…”