Monoterpene indole alkaloids (MIAs) are pharmacologically important secondary metabolites mainly characterized in terrestrial plants, but their potential occurrence and regulation in diatoms remain poorly explored. This study investigated whether the marine diatom Thalassiosira rotula contains genes associated with the MIA biosynthetic pathway and whether these genes are transcriptionally responsive to abiotic stress. An integrated approach was applied, combining transcriptomic and genomic data mining with in-silico differential expression analysis. The identified putative genes were evaluated across the MIA pathway, including the mevalonate and methylerythritol phosphate precursor pathways and downstream iridoid, catharanthine- and vinblastine-related branches. Expression responses were assessed under silica depletion, resting-cell formation induced by nitrogen deprivation, and phosphate enrichment associated with temperature stress.
The strongest putative gene support was found for the precursor pathways, while downstream branches resulted in sequences partially represented. Several iridoid- and downstream-associated genes were detected, but the data did not support a complete plant-like MIA pathway. In-silico differential expression analysis revealed condition-specific regulation: silica depletion induced selective trends of expression, resting-cell formation was associated with transcriptional downregulation with selective secologanin synthase induction, and phosphate enrichment with temperature stress generated the strongest transcriptional reorganization. These findings establish a framework for future functional and metabolomic validation.
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