Abstract
BackgroundThe yeast Xanthophyllomyces dendrorhous produces carotenoids of commercial interest, including astaxanthin and β-carotene. Although carotenogenesis in this yeast and the expression profiles of the genes controlling this pathway are known, the mechanisms regulating this process remain poorly understood. Several studies have demonstrated that glucose represses carotenogenesis in X. dendrorhous, suggesting that this pathway could be regulated by catabolic repression. Catabolic repression is a highly conserved regulatory mechanism in eukaryotes and has been widely studied in Saccharomyces cerevisiae. Glucose-dependent repression is mainly observed at the transcriptional level and depends on the DNA-binding regulator Mig1, which recruits the co-repressor complex Cyc8–Tup1, which then represses the expression of target genes. In this work, we studied the regulation of carotenogenesis by catabolic repression in X. dendrorhous, focusing on the role of the co-repressor complex Cyc8–Tup1.ResultsThe X. dendrorhous CYC8 and TUP1 genes were identified, and their functions were demonstrated by heterologous complementation in S. cerevisiae. In addition, cyc8 − and tup1 − mutant strains of X. dendrorhous were obtained, and both mutations were shown to prevent the glucose-dependent repression of carotenogenesis in X. dendrorhous, increasing the carotenoid production in both mutant strains. Furthermore, the effects of glucose on the transcript levels of genes involved in carotenogenesis differed between the mutant strains and wild-type X. dendrorhous, particularly for genes involved in the synthesis of carotenoid precursors, such as HMGR, idi and FPS. Additionally, transcriptomic analyses showed that cyc8 − and tup1 − mutations affected the expression of over 250 genes in X. dendrorhous. ConclusionsThe CYC8 and TUP1 genes are functional in X. dendrorhous, and their gene products are involved in catabolic repression and carotenogenesis regulation. This study presents the first report involving the participation of Cyc8 and Tup1 in carotenogenesis regulation in yeast.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0597-1) contains supplementary material, which is available to authorized users.
Highlights
The yeast Xanthophyllomyces dendrorhous produces carotenoids of commercial interest, including astaxanthin and β-carotene
Considering that catabolic repression is an important regulatory mechanism that is widely conserved among eukaryotes, and given that results from previous studies suggest that carotenogenesis in X. dendrorhous could be regulated by this mechanism, the aim of this work was to study the catabolic repression regulatory mechanism and carotenogenesis in X. dendrorhous, focusing on the role of the co-repressor complex Cyc8–Tup1
General characterization of catabolic repression in X. dendrorhous First, we studied whether the X. dendrorhous wild-type strain (UCD 67–385, ATCC 24230) demonstrates a functional catabolic repression mechanism in which the Cyc8 and Tup1 proteins would play an important role
Summary
The yeast Xanthophyllomyces dendrorhous produces carotenoids of commercial interest, including astaxanthin and β-carotene. Carotenogenesis in this yeast and the expression profiles of the genes con‐ trolling this pathway are known, the mechanisms regulating this process remain poorly understood. Several studies have demonstrated that glucose represses carotenogenesis in X. dendrorhous, suggesting that this pathway could be regulated by catabolic repression. Phytoene is the first carotenoid synthesized in the pathway, produced from GGPP by the bifunctional enzyme phytoene-βcarotene synthase (PBS, encoded by the crtYB gene) [11]. Phytoene is transformed to lycopene by phytoene desaturase (encoded by the crtI gene) [12] Both ends of lycopene are cyclized by PBS to produce β-carotene [11]. Because astaxanthin synthase is a cytochrome P450 enzyme, it requires cytochrome P450 reductase, which is encoded by the crtR gene in X. dendrorhous, as an electron donor for its catalysis [15]
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