Transcriptomics of Plant Stress Response and Secondary Metabolite Biosynthesis in Morinda lucida Under Simulated Climate Stress: Implications for Pharmacognostic Quality

Climate change is projected to significantly alter the phytochemical composition and pharmacognostic quality of medicinal plants across Nigeria's phytogeographical zones, with implications for the consistency and safety of herbal medicines derived from field-grown species. Morinda lucida, a pharmacognostically significant rainforest species used across South South and South West Nigeria, is expected to face increasing heat and drought stress under climate change scenarios. This study investigates the transcriptomic regulation of secondary metabolite biosynthesis genes and its effect on pharmacognostic phytochemical output in Morinda lucida under simulated heat (37 degrees C), drought (15% PEG 6000-induced), and combined climate stress conditions. Controlled glasshouse experiments were conducted at the University of Ibadan with three-year-old Morinda lucida specimens. Transcriptomic profiling was performed by RNA-Seq on leaf and root tissue at stress induction timepoints of 7, 14, and 21 days. DESeq2 differential gene expression analysis identified stress-responsive biosynthesis genes. Key anthraquinone biosynthesis genes (CYP450s, polyketide synthases) and alkaloid pathway transcription factors were monitored. Metabolomic output was quantified by UHPLC-HRMS. Drought stress significantly upregulated anthraquinone biosynthesis transcription, resulting in 38% elevation of rubiadin and nordamnacanthal content. Heat stress alone suppressed total phenolic biosynthesis. Combined stress produced complex non-additive effects on secondary metabolite profiles. These findings provide foundational data for climate-responsive quality specifications for Morinda lucida and recommend adaptive harvesting guidelines for quality-conscious herbal production. Keywords: Morinda lucida, transcriptomics, climate stress, anthraquinone, pharmacognostic quality