Biochemical Characteristics Of Selenium - Enriched Chlamydomonas Reinhardtii And Its Transcriptology

Selenium is an essential trace element for human and animals, selenium deficiency can lead to various diseases. However, due to the relatively high toxicity of inorganic selenium, a safe and effective way of selenium supplementation becomes a research hotspot. According to the brief growth cycle, simple culture conditions, and superiorse-enrich ability, algae attracted broad attention. The selenoprotein abundant Chlamydomonas reinhardtii is selected in this study to investigate its biological characteristics of rich in selenium and Se-response genes expression, and to obtain better insight into the effects of Se on algae metabolism and organic selenium enrichment mechanisms, the transcriptome of C. reinhardtii cultured with or without selenite was studied by using RNA-seq.To determine the optimal concentration of Se in the culture medium, experiment with different concentrations of sodium selenite in the medium was examed. Meanwhile the experiment of different phase that Se supplemented to impact the Se content of C. reinhardtii was studied too, and dynamic trend of organic and total selenium enrichment. Transcriptome level of Se supplementation also studied by Illumina Hiseq2000 sequencing platform. Kinds of C.reinhardtii gene sequences of coding selenoproteins were predicted through BLAST, and nine of them were selected for real-time fluorescence quantitative PCR to study the inorganic Se supplemention impact on C. reinhardtii selenoprotein under RNA level.The results indicate that total selenium and organic selenium content in C. reinhardtii both increased with extended culture time, and the exponential phase of growth is the main period of enrichment of total organic selenium. On stationary phase of growth, metabolic activity of algae decreased, and total selenium enrichment C. reinhardtii CC849 becomes slow with stable organic Se content. The total selenium content decreased slightly on late stationary/decline phase. On late log phase of C. reinhardtii combine with the concentration of sodium selenite supplemented at 3mg/L, total selenium up to about 2600μg/g with organic selenium content of about 2000μg/g. Transcriptome sequencing result discovered 111 new genes, including 14 genes annotated to COG,50 annotations to GO, and 5 annotations to KEGG. Through the new gene pathway analysis, the new genes are mainly related to the process of photosynthesis, aminoacyl transfer RNA synthesis and RNA transport processes. It was found that 194 differentially expressed genes, 138 genes were upregulated, and 56 genes were downregulated. For differences in gene annotation, COG results suggest major differences include in gene transcription, signal transduction mechanisms, coenzyme transport and metabolism, inorganic ion transport and metabolism, replication, recombination and repair, and energy production and conversion as well as post-translational modification, protein turnover and chaperones are concerned.30 differentially expressed genes annotated to KEGG, are mainly involved in 25 pathways. QPCR result suggest that selenoprotein encoding genes expression increased significantly in accordance with results of RNA-seq.