De novo transcriptome analysis deciphered polyoxypregnane glycoside biosynthesis pathway in Gymnema sylvestre

Abstract

Gymnema sylvestre is an important medicinal plant containing antidiabetic activity. Through de novo transcriptomic study,the pathways of polyoxypregnane glycosides were explored and candidate genes of these pathways were identified in G.sylvestre. High-quality raw reads were assembled into transcripts which resulted in 193,615 unigenes. These unigenes furtherdecoded 58,274 coding DNA sequences (CDSs). Functional annotation of predicted CDSs was carried out using the proteindatabases, i.e., NCBI’s non-redundant, Uniprot and Pfam. Eukaryotic orthologous group (KOG) classification and transcriptionfactor analysis has revealed most CDS-enriched categories as “Signal transduction mechanism” and “Basic Helix loophelix” (bHLH) transcription factor family, respectively. A total of 16,569 CDSs were assigned minimum one Gene Ontology(GO) term. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis disclosed 235 CDSs which representedtotal 27 genes of pregnane glycoside pathways and 19 CDSs represented 10 important enzymes of polyoxypregnane glycosidebiosynthesis, i.e., sterol 24-C-methyltransferase, cycloeucalenol cycloisomerase, Δ14-sterol reductase, C-8,7 sterol isomerase,sterol methyltransferase 2, C-5 sterol desaturase, sterol Δ7 reductase, Δ24 sterol reductase, 3β-hydroxysteroid dehydrogenaseand progesterone 5β reductase (5βPOR). This transcriptome analysis provided an important resource for future functionalgenomic studies in G. sylvestre.