Identification And Analysis Of Genes Related To Selenium Assimilation And Metabolism In Tea Plant Roots

Selenium(Se) is one of the important life elements, and has been recognized as an essential trance element for humans by FAO/IAEA/WHO. Human bodies must get selenium from inorganic Se medicament or organic Se-enriched foods, and organic Se can be more easily absorbed than inorganic for its good bioactivity and availability. Tea is an ideal Se supplemental source for its higher Se concentration compared to general crops, as well as the higher percentage in total of organoselenium. Obtaining better understanding of the selenium accumulation and Se-enriched mechanism in tea plant could provide the theory basis for breeding the Se-enriched tea plants.In this dissertation, RNA-sequencing(RNA-Seq) was employed on the Se-treatment tea plant, S-treatment tea plant and control(without treatment) to reveal the differently expressed genes among three groups. On the basis of comparative transcriptome profiling analyses, we identified plenty of Se-responsive genes, including inorganic ion transporter genes, ABC transporter genes and the genes involved in sulfur-relate metabolic pathways. Additionally, the sulfate transporter gene CsSULTR3.5 in tea plant was cloned and the bioinformatics characteristics were analyzed. The main results were summarized as follows:1. We carried out RNA-Seq on Se-treatment plant, S-treatment plant and control plant to obtain comprehensive gene expression profiles. A total of 104,990 unigenes were acquired with an average length of 732 bp and N50 length of 1,024 bp. After searching all-unigenes against with public protein databases, 36,186 unigenes were functionally annotated. These unigenes were mainly enriched in metabolism pathways.2. We identified 7,877 differentially expressed unigenes(DEGs) in the comparison of Se treatment to CK, in while 4,845 unigenes were up-regulated and 3,032 unigenes were down-regulated. In addition, there are 2,313 DEGs were identified in S treatment, including 1,028 up-regulated and 1,285 down-regulated unigenes. Furthermore, 20 DEGs were randomly selected to validate the reliability of RNA-Seq by qRT-PCR. Among the transcriptomic comparisons, many metabolism pathways and genes responding to Se were obtained. For example, cysteine and methionine metabolism, glutathione metabolism and sulfur metabolism pathways were enriched, and ATPS1/3, APR, SAT, GS and CS were upregulated under Se treatment.3. Among the differential expression genes, we identified 5 inorganic ion transporter genes, including 3 sulfate transporter genes SULTR1.3 and SULTR3.5, 1 molybdate transporter gene(MoT1) and 2 phosphate transporter genes(PiT), most of them were upregulated upon the treatment of Selenate. Additionally, we identified 16 DEGs encoding ABC transporters, including 4 ABCBs, 4 ABCCs, 5 ABCGs, 2 ABCAs and 1 ABCF subfamily numbers. These results suggest that ABC transporters maybe play a role in selenium movement and accumulation in tea plant.4. The cDNA of putative sulfate transporter(CsSULTR3.5) gene(GenBank accession number KP984500) was cloned from tea plant. Bioinformatics analysis indicated that the cDNA of CsSULTR3.5 containing 1,914 bp ORF encoded 637 amino acid residues with a putative molecular mass of 70.38 kD. It was predicted that CsSULTR3.5 was a non-secretory protein without a signal peptide. CsSULTR3.5 could be located in the plasma membrane with 12 transmembrane domains. The real-time PCR analysis showed that CsSULTR3.5 transcripts were expressed both in roots and leaves and significantly increased upon the treatment of Na2SO4 and Na2SeO4.