Combined Fungal Elicitor and Methyl Jasmonate Enhance Alkaloid Accumulation in Catharanthus roseus Suspension Cultures: An Integrated Molecular and Phytochemical Study

Suspension cultures of Catharanthus roseus provide an alternative system for studying the regulation of terpenoid indole alkaloid (TIA) biosynthesis and the production of pharmaceutically important metabolites. This study evaluated the effects of the endophytic fungal elicitor RN3 (Chaetomium funicola) and methyl jasmonate (MeJA) on alkaloid accumulation and TIA pathway-associated gene expression in C. roseus suspension cultures. Co-elicitation with 1% RN3 and 150 μM MeJA produced the highest total alkaloid accumulation (14.68 mg g−1 dry weight), representing a 58.9% increase over the untreated control. HPLC analysis detected catharanthine in cultures treated with 1% RN3, whereas both catharanthine and vindoline were detected after co-treatment with 1% RN3 and 150 μM MeJA. Phytochemical investigation of the co-elicited cultures resulted in the isolation of five compounds, including the previously undescribed lignan catharalignan, the alkaloids β-carboline and tryptoline, (+)-syringaresinol-β-D-glucoside, and L-thymidine. RT-qPCR analysis showed that the expression of the transcription factor genes ORCA2 and ORCA3 remained significantly elevated throughout the 3-day period following elicitation, whereas the tested TIA pathway structural genes showed limited transcriptional changes. These findings indicate that RN3, particularly in combination with MeJA, enhances alkaloid accumulation and modulates the transcriptional response of TIA pathway-associated genes.