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RNA-seq of phytoene desaturase knockout carotenoid-deficient microalgal mutants generated by cas9-ribonucleoprotein complexes

ABSTRACT: Phytoene desaturase (PDS; EC 1.3.5.5) is a key enzyme of the carotenoid biosynthetic pathway, catalyzing the desaturation of phytoene, precursor of all carotenoids. In this study, several PDS knockout (PDS-KO) transformants of the chlorophyte microalga Chlamydomonas reinhardtii were generated using a reverse genetics strategy. Two single guide RNAs (sgRNA) were designed to target the first exon of the PDS gene, and pre-assembled Cas9 ribonucleoprotein (RNPs) complexes were delivered into microalgal nuclei by electroporation. Multiple white PDS-KO transformants were successfully obtained by this approach, and three independent transformant lines were subsequently characterized. By integrating ultrastructural, pigment and transcriptomic analyses of dark-grown cells of several PDS-KO carotenoid-deficient mutants in comparison with the parental strain, it was demonstrated that carotenoids are indispensable components of multiple cellular architectures. Chromatographic analysis confirmed that the only carotenoid accumulated in these transformants was phytoene, which lacks the critical structural and photoprotective functions of its colored derivatives. Transmission Electron Microscopy (TEM) observations revealed profound ultrastructure alterations, including poorly developed chloroplasts and effects on other cellular structures that were either absent or severely disorganized. Consistently, clustering differentially expressed genes into functional groups revealed downregulation of pathways associated with photosynthesis, chlorophyll and carotenoid biosynthesis, ribosome biogenesis, and vesicle and membrane trafficking in the PDS-KO lines. Conversely, upregulation of regulatory and retrotransposon-inducing genes was observed. These findings underscore the central metabolic role of colored carotenoids in plant cells, highlighting their essential contribution to cellular homeostasis and photosynthetic competence

ORGANISM(S): Chlamydomonas reinhardtii

PROVIDER: GSE319264 | GEO | 2026/02/12

REPOSITORIES: GEO

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Project description:To obtain insight in the genome-wide response of heterologous carotenoid production in Saccharomyces cerevisiae, we have analyzed the transcriptome of S. cerevisiae strains overexpressing carotenogenic genes from the yeast Xanthophyllomyces dendrorhous. For this purpose, two strains producing different levels of carotenoids were grown in carbon-limited continuous cultures and genome-wide expression was analyzed. The strain producing low carotenoid levels did not exhibit a clear genome-wide transcriptional response, suggesting that low carotenoid levels do not result in cellular stress. Transcriptome analysis of a strain producing high carotenoid levels resulted in specific induction of genes involved in pleiotropic drug resistance (PDR). These genes encode ATP-binding cassette (ABC) type transporters and major facilitator transporters which are involved in secretion of toxic compounds out of cells. Our results suggest that production of high amounts of carotenoids in S. cerevisiae lead to toxicity and that these cells are prone to secrete carotenoids out of the cell. Indeed, secretion of ï¢-carotene into sunflower oil was observed upon addition of this hydrophobic solvent to the growth medium. Finally, it was observed that deletion of the ABC transporter pdr10, one of the induced PDR transporters, highly decreased the transformation efficiency of an episomal vector containing carotenogenic genes. The few colored transformants that were obtained had decreased growth rates and lower carotenoid production levels compared to control strains transformed with the same carotenogenic genes. These results indicate that Pdr10 might be specifically involved in carotenoid tolerance in S. cerevisiae strains. Experiment Overall Design: The genome wide transcriptional response of S. cerevisiae cells that heterologously produce carotenoids might provide information concerning the impact of carotenoid production on yeast physiology and might identify bottlenecks relevant for the production of these compounds. DNA microarray experiments have been proven to be a powerful tool to study the genome wide transcriptional response of S. cerevisiae to changes of the physiological state and the environment (for example 3,. Genomics approaches on cells producing heterologous metabolites to study their impact on yeast physiology have not been reported yet for S. cerevisiae. Additionally, most transcriptome studies with S. cerevisiae have been performed with cells grown in shake flasks cultures. The main drawback of shake flask cultivation is that the environment is continuously changing, which may be of high influence on carotenoid production, and interpretation of transcriptome data . Chemostat cultivation offers advantages for studies with DNA microarrays because it enables cultivation of microorganisms under tightly defined environmental conditions. An interlaboratory comparison of transcriptome data obtained in chemostat cultures has indeed demonstrated that the accuracy and reproducibility of this approach are superior to those obtained in previous studies with shake-flask cultures .

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RNA-seq of phytoene desaturase knockout carotenoid-deficient microalgal mutants generated by cas9-ribonucleoprotein complexes

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