Influence of cellular differentiation and elicitation on intermediate and late steps of terpenoid indole alkaloid biosynthesis in Catharanthus roseus

The invaluable antineoplastic bisindole alkaloids of Catharanthus roseus and their precursor, vindoline, are not produced in cell cultures. The intricacies involved in endogenous (cellular differentiation) and exogenous (elicitation) regulation of their biosynthesis need to be dissected out for favorable exploitation. This study aimed at elucidating the effect of Pythium aphanidermatum homogenate and methyl jasmonate (MeJa) on in vitro cultures (of cv. 'Dhawal') representing increasing level of differentiation (suspension < callus < shoots) in terms of alkaloid accumulation and transcript abundance of strictosidine beta-d-glucosidase (SGD) and acetyl-CoA: 4-O-deacetylvindoline 4-O-acetyl-transferase (DAT) genes, representing intermediate and late steps, respectively, of terpenoid indole alkaloid biosynthesis. Elicitation of suspension cultures caused transcriptional upregulation of SGD and enhanced the accumulation of total alkaloids but did not produce vindoline as DAT transcripts were always found to be absent in suspension-cultured cells. Vindoline was also not detected in unelicited and MeJa-treated callus but appeared upon elicitation with fungal homogenate for 24 h that coincided with maximal DAT transcription. Transcript levels of both genes increased upon elicitation of callus but remained below levels present in the mature plant leaf. Elicitation caused appearance of vindoline in shoots and increased the transcript abundance of both genes beyond levels observed in the mature plant leaf. Differentiation was essential for expression of DAT but not SGD, and vindoline biosynthetic potential increased with it.