Illumina-based Whole De Novo Transcriptome Profiling and Diosgenin Biosynthetic pathway of Tribulus terrestris: A Medicinal herb

Tribulus terrestris L. (Chota gokhuru), an annual herb of the Zygophyllaceae family accumulates steroidal-type triterpenoids of diosgenin in root, leaf, fruit, which have been used as a traditional medicine to cure steroidal hormonal diseases such as estrogen, progesterone, and cardiovascular and urogenital. However, to date, the diosgenin biosynthetic pathway of T. terrestris is unknown. In this research paper, identification of candidate genes involved in bioactive compounds (diosgenin) was conducted via whole transcriptome profiling of T. terrestris using the Illumina HiSeq sequencing platform, which generated 482 million reads. RNA-Seq reads were assembled and clustered into 148871 unigenes. NCBI non-redundant (NR) and Swiss-Prot databases search anchored 50% unigenes with the functional annotations based on similarities of sequence. Further, in Gene Ontology and KEGG-KAAS pathways, a total of 126 unigenes were highly expressed in the terpenoids backbone biosynthesis, in which diosgenin pathways (two genes of glycolytic, three genes of mevalonate, two genes of MEP/DOX, one gene of mono-terpenoids, and seven genes of steroidal pathways) were identified. In addition, 9 genes were randomly selected for confirmation through real-time PCR. T. terrestris showed the highest homology with the Citrus sinensis and Juglans regia. 27478 unigenes of transcription factors were assembled, in which top ten transcription factors were highly expressed. A total of 17623 SSR was assembled, amongst them unigenes of di-nucleotide were highly repeated. This research work will improve our understanding of the diosgenin pathway and lay the groundwork for future molecular research on metabolic engineering, as well as raise diosgenin content in T. terrestris.