Responses of defense signals, biosynthetic gene transcription and taxoid biosynthesis to elicitation by a novel synthetic jasmonate in cell cultures of Taxus chinensis

Recently novel synthetic jasmonate derivatives were shown to have very powerful stimulating effects on the biosynthesis of taxuyunnanine C (Tc) by Taxus chinensis cells (Biotech Bioeng, 86:595; ibid. 86: 809, 2004). To provide an insight into the elicitation mechanism of the newly synthesized elicitors, by taking 2-hydroxyethyl jasmonate (HEJ, at 100 μM) as a typical example, in this work the defense signals were detected and their influences on the expression of important genes in taxoid biosynthetic pathway were examined in cell cultures of T. chinensis. The oxidative burst (induced H₂O ₂ production) was confirmed, and the induction of lipoxygenase (LOX) activity and intracellular jasmonate acid (JA) synthesis was found. The gene transcription of geranylgeranyl diphosphate synthase (GGPPs) and taxa-4(5), 11(12)-diene synthase (TS) was up-regulated by HEJ elicitation compared to control. Inhibition of JA biosynthesis by a putative LOX inhibitor, ibuprofen (IBU), effectively depressed the HEJ-induced up-regulation of GGPPs and TS gene transcription levels. In contrast, the inhibition of H₂O₂ production by membrane NADPH oxidase inhibitor, diphenylene iodonium (DPI), did not affect the transcriptions of those genes. For the HEJ-induced Tc production, it was suppressed with addition of DPI or IBU. The results suggest that both H₂O₂ and JA signals were involved in HEJ-induced Tc biosynthesis, and JA mediated the induction of GGPPs and TS genes expression, but H₂O₂ was not essential to activate them. Finally, a signal transduction cascade from defense signal response to activated transcription of taxoid biosynthetic genes and enhanced Tc production is proposed.