Abstract
Xanthophyllomyces dendrorhous is a basidiomycete yeast that synthesizes carotenoids, mainly astaxanthin, which are of great commercial interest. Currently, there are many unknown aspects related to regulatory mechanisms on the synthesis of carotenoids in this yeast. Our recent studies showed that changes in sterol levels and composition resulted in upregulation of genes in the mevalonate pathway required for the synthesis of carotenoid precursors, leading to increased production of these pigments. Sterol Regulatory Element-Binding Proteins (SREBP), called Sre1 in yeast, are conserved transcriptional regulators of sterol homeostasis and other cellular processes. Given the results linking sterols and carotenoids, we investigated the role of SREBP in sterol and carotenoid synthesis in X. dendrorhous. In this study, we present the identification and functional characterization of the X. dendrorhous SRE1 gene, which encodes the transcription factor Sre1. The deduced protein has the characteristic features of SREBP/Sre1 and binds to consensus DNA sequences in vitro. RNA-seq analysis and chromatin-immunoprecipitation experiments showed that genes of the mevalonate pathway and ergosterol biosynthesis are directly regulated by Sre1. The sre1- mutation reduced sterol and carotenoid production in X. dendrorhous, and expression of the Sre1 N-terminal domain (Sre1N) increased carotenoid production more than twofold compared to wild-type. Overall, our results indicate that in X. dendrorhous transcriptional regulation of genes in the mevalonate pathway control production of the isoprenoid derivatives, carotenoids and sterol. Our results provide new insights into the conserved regulatory functions of SREBP/Sre1 and identify pointing to the SREBP pathway as a potential target to enhance carotenoid production in X. dendrorhous.
Highlights
Xanthophyllomyces dendrorhous is a basidiomycete yeast that synthesizes carotenoids, mainly astaxanthin, pigment of great commercial interest widely used in aquaculture and in nutraceutical, pharmaceutical and cosmetics industry (Galasso et al, 2017)
Considering the facts described above suggesting that sterol and carotenoid biosynthesis in X. dendrorhous may be regulated by a common mechanism controlled by sterols, we investigated the function of X. dendrorhous Sterol Regulatory Element-Binding Proteins (SREBP)
The predicted Sre1 protein from X. dendrorhous has the characteristic features of SREBP/Sre1 proteins described in other organisms
Summary
Xanthophyllomyces dendrorhous is a basidiomycete yeast that synthesizes carotenoids, mainly astaxanthin, pigment of great commercial interest widely used in aquaculture and in nutraceutical, pharmaceutical and cosmetics industry (Galasso et al, 2017). Carotenoids are yellow to red pigments that are involved in photoprotective mechanisms (Alcaíno et al, 2014), among other functions. These pigments are isoprenoid compounds, which are a large and diverse family of natural products consisting of over 40,000 structurally different compounds isolated from animals, plants and microorganisms (Misawa, 2011). In non-photosynthetic eukaryotes such as yeasts, the universal isoprenoid building blocks, isopentenyl pyrophosphate (IPP, C5) and its isomer dimethylallyl pyrophosphate (DMAPP, C5), are synthesized by the mevalonate (MVA) pathway (Schmidt et al, 2011). Sterols, which are essential structural and regulatory lipids of eukaryotic cells, derive from the MVA pathway. Several Phaffia rhodozyma (the anamorphic state of X. dendrorhous; Golubev, 1995), astaxanthin-overproducing mutants obtained by random mutagenesis showed a lower ergosterol content, the main fungal sterol, when compared to the parent strains (Miao et al, 2010, 2011)
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