Abstract
Swertia mussotii Franch. is an important traditional Tibetan medicinal plant with pharmacological properties effective in the treatment of various ailments including hepatitis. Secoiridoids are the major bioactive compounds in S. mussotii. To better understand the secoiridoid biosynthesis pathway, we generated transcriptome sequences from the root, leaf, stem, and flower tissues, and performed de novo sequence assembly, yielding 98,613 unique transcripts with an N50 of 1,085 bp. Putative functions could be assigned to 35,029 transcripts (35.52%) based on BLAST searches against annotation databases including GO and KEGG. The expression profiles of 39 candidate transcripts encoding the key enzymes for secoiridoid biosynthesis were examined in different S. mussotii tissues, validated by qRT-PCR, and compared with the homologous genes from S. japonica, a species in the same family, unveiling the gene expression, regulation, and conservation of the pathway. The examination of the accumulated levels of three bioactive compounds, sweroside, swertiamarin, and gentiopicroside, revealed their considerable variations in different tissues, with no significant correlation with the expression profiles of key genes in the pathway, suggesting complex biological behaviours in the coordination of metabolite biosynthesis and accumulation. The genomic dataset and analyses presented here lay the foundation for further research on this important medicinal plant.
Highlights
Swertia mussotii Franch. is an important traditional Tibetan medicinal plant with pharmacological properties effective in the treatment of various ailments including hepatitis
De novo transcriptome analysis is an excellent platform for generating comprehensive information of the gene space in an organism for the discovery of novel genes, development of molecular markers, and construction of gene expression networks for specific tissues/organs
To generate a transcriptome database for S. mussotii, twelve RNAseq libraries were constructed from the root, stem, leaf, and flower tissues collected from three individual plants
Summary
Gene name acetyl-CoA C-acetyltransferase acetyl-CoA C-acetyltransferase acetyl-CoA C-acetyltransferase hydroxymethylglutaryl-CoA synthase hydroxymethylglutaryl-CoA synthase hydroxymethylglutaryl-CoA synthase hydroxymethylglutaryl-CoA synthase hydroxymethylglutaryl-CoA reductase hydroxymethylglutaryl-CoA reductase hydroxymethylglutaryl-CoA reductase hydroxymethylglutaryl-CoA reductase mevalonate kinase phosphomevalonate kinase diphosphomevalonate decarboxylase diphosphomevalonate decarboxylase 1-deoxy-D-xylulose-5-phosphate synthase 1-deoxy-D-xylulose-5-phosphate synthase 1-deoxy-D-xylulose-5-phosphate synthase 1-deoxy-D-xylulose-5-phosphate synthase 1-deoxy-D-xylulose-5-phosphate reductoisomerase 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase (E)-4-hydroxy-3-methylbut-2-enyl-diphosphate synthase 4-hydroxy-3-methylbut-2-en-1-yl diphosphate reductase isopentenyl-diphosphate delta-isomerase isopentenyl-diphosphate delta-isomerase geranyl diphosphate synthase geranyl diphosphate synthase geranyl diphosphate diphosphatase geraniol 10-hydroxylase 8-hydroxygeraniol oxidoreductase iridoid synthase iridoid oxidase 7-deoxyloganetic acid glucosyl transferase 7-deoxyloganic acid hydroxylase loganic acid O-methyltransferase secologanin synthase secologanin synthase. To examine the possible associations of gene expression in the secoiridoid pathway with the metabolite products, we determined the contents of three bioactive compounds of the secoiridoid pathway, sweroside, swertiamarin, and gentiopicroside, in four tissues (root, leaf, stem, and flower). The expression profiles of the metabolic biosynthesis genes in different tissues did not show significant correlations in relation to the metabolite contents This result agrees with several previous reports, including the study in which the expression levels of the genes involved in the phenylpropanoid pathway did not show significant correlations with the accumulation pattern of shikonin[59]. The transcriptome data represent the first genomics resource for S. mussotii and lay the foundation for future research towards the improvement of this ethnomedicinal crop through genetics, genomics, and biotechnological approaches
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