Abstract
Trillium govanianum, an endangered medicinal herb native to the Himalaya, is less studied at the molecular level due to the non-availability of genomic resources. To facilitate the basic understanding of the key genes and regulatory mechanism of pharmaceutically important biosynthesis pathways, first spatial transcriptome sequencing of T. govanianum was performed. 151,622,376 (~11.5 Gb) high quality reads obtained using paired-end Illumina sequencing were de novo assembled into 69,174 transcripts. Functional annotation with multiple public databases identified array of genes involved in steroidal saponin biosynthesis and other secondary metabolite pathways including brassinosteroid, carotenoid, diterpenoid, flavonoid, phenylpropanoid, steroid and terpenoid backbone biosynthesis, and important TF families (bHLH, MYB related, NAC, FAR1, bZIP, B3 and WRKY). Differentially expressed large number of transcripts, together with CYPs and UGTs suggests involvement of these candidates in tissue specific expression. Combined transcriptome and expression analysis revealed that leaf and fruit tissues are the main site of steroidal saponin biosynthesis. In conclusion, comprehensive genomic dataset created in the current study will serve as a resource for identification of potential candidates for genetic manipulation of targeted bioactive metabolites and also contribute for development of functionally relevant molecular marker resource to expedite molecular breeding and conservation efforts in T. govanianum.
Highlights
The raw reads generated from Illumina GAIIx sequencing of all the four tissues were deposited at National Centre for Biotechnology Information (NCBI) Sequence Read Archive (SRA) database with accession number: SRP090722 under the Bioproject- PRJNA345073
Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis helps in understanding the biological function and interaction of genes related to the primary and secondary metabolites such that mapping of transcripts with the KEGG database in this study identified all the genes related to steroidal saponin pathway
All the key genes involved in steroidal saponin biosynthesis pathway can be futuristically explored for upscaling of the targeted bioactive molecules at the industrial scale
Summary
Don (Family: Melanthiaceae), prevalently known as “Nag chhatri” or “Satva”, is an endangered perennial herb with multiple therapeutic properties It is the only species of the genus Trillium, native to the Himalaya representing scattered distribution from Nanga Parbat to Namcha Barwa at an altitude range of 2700 m to 4000 m1,2. Extraction of T. govanianum before the maturation of seeds This has resulted in rapid depletion of its natural populations and makes this species endangered in the Himalaya[10,11]. Medicinal and therapeutic importance of the species is due to the occurrence of steroidal saponins, one of the most structurally diverse and extensively distributed secondary metabolites in plants[12]. T. govanianum accumulates almost triple diosgenin content (~6.0%) compared to other explored medicinal plant species, namely Asparagus spp., Chlorophytum spp., Dioscorea spp. and Trigonella spp[19]. Several hydroxylation and glycosylation steps catalyzed by CYP450s and UGTs respectively, contributes to the structural and functional diversification of various steroidal saponins[23]
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