Genome-wide transcriptional analysis unveils the molecular basis of organ-specific expression of isosteroidal alkaloids biosynthesis in critically endangered Fritillaria roylei Hook

Abstract Fritillaria roylei Hook. is a critically endangered high altitude Himalayan medicinal plant species with rich source of pharmaceutically active structurally diverse steroidal alkaloids. Nevertheless, except few marker compounds, the chemistry of the plant remains unexplored. Therefore, in the current study, transcriptome sequencing efforts were made to elucidate isosteroidal alkaloids biosynthesis by creating first organ-specific genomic resource using bulb, stem, and leaf tissues derived from natural populations of Indian Himalayan region. Overall, 349.9 million high quality paired-end reads obtained using NovaSeq 6000 platform were assembled (de novo) into 82,848 unigenes and 31,061 isoforms. Functional annotation and organ specific differential expression (DE) analysis identified 2488 significant DE transcripts, grouped into three potential sub-clusters (sub-cluster I: 728 transcripts; sub-cluster II: 446 transcripts and Sub-cluster III: 1314 transcripts). Subsequently, pathway enrichment (GO, KEGG) and protein-protein network analysis revealed significantly higher enrichment of phenyl-propanoid and steroid backbone including terpenoid, sesquiterpenoid and triterpenoid biosynthesis in bulb. Additionally, upregulated expression of cytochrome P450, UDP-dependent Glucuronosyltransferase families and key transcription factor families (FAR1, bHLH, GRAS, C2H2, TCP and MYB) suggests ‘bulb’ as a primary site of MVA mediated isosteroidal alkaloids biosynthesis. The comprehensive elucidation of molecular insights in this study is a first step towards the understanding of isosteroidal alkaloid biosynthesis pathway in F. roylei. Furthermore, key genes and regulators identified here can facilitate metabolic engineering of potential bioactive compounds at industrial scale.