Endophytes enhance the production of root alkaloids ajmalicine and serpentine by modulating the terpenoid indole alkaloid pathway in Catharanthus roseus roots

AIM: The aim of this study was to identify and characterize promising endophytes capable of enhancing the content of root alkaloids ajmalicine and serpentine in low alkaloid yielding genotype of Catharanthus roseus cultivar Prabal and the possible mechanisms involved. METHOD AND RESULT: Of the four strains isolated from alkaloid-rich genotype of C. roseus cultivar Dhawal, endophytic strains CATDLF5 (Curvularia sp.) and CATDLF6 (Choanephora infundibulifera) enhanced serpentine content by 211.7-337.6%, while CATDRF2 (Aspergillus japonicus) and CATDS5 (Pseudomonas sp.) increased the content of ajmalicine by 123.4-203.8% in cultivar Prabal. Upregulated expression of key genes, geraniol 10-hydroxylase, tryptophan decarboxylase and strictosidine synthase involved in terpenoid indole alkaloid (TIA) biosynthetic pathway was observed in endophyte inoculated plants. Upregulated Octadecanoid-derivative Responsive Catharanthus AP2/ERF domain transcription activators like ORCA3 while, and downregulation of transcriptional repressor, ZCTs (Cys2/His2-type zinc finger protein family) enhanced the expression of genes for secondary metabolite production in endophyte-inoculated plants. CONCLUSION: The present work concluded that the selected endophytes of C. roseus can enhance the ajmalicine and serpentine contents by modulating the expression of structural and regulatory genes of TIA biosynthetic pathway in root. SIGNIFICANCE AND IMPACT OF THE STUDY: Endophytes can play an important role to enhance in planta content of pharmaceutically important alkaloids in C. roseus and can therefore be useful in reducing the cost of production of important alkaloids.