Different secondary metabolic responses to MeJA treatment in shikonin-proficient and shikonin-deficient cell lines from Arnebia euchroma (Royle) Johnst

Abstract

© 2014, Springer Science+Business Media Dordrecht. The administration of methyl jasmonate (MeJA) to A. euchroma suspension-cultured cells elicited distinct responses from a red shikonin-proficient cell line (RCL) and a white shikonin-deficient cell line (WCL). Specifically, MeJA promoted the accumulation of shikonin derivatives, shikonofuran derivatives and rosmarinic acid in the RCL, but no shikonin derivatives accumulated in the WCL. Moreover, MeJA promoted the WCL to produce several unusual shikonofuran derivatives that are thought to be derived from geranylhydroquinone (GHQ), a key intermediate in the biosynthesis of shikonin derivatives. To the best of our knowledge, herein we identified shikonofuran derivatives in A. euchroma for the first time. Further, we found that these secondary metabolic products can be induced by MeJA rapidly (within 1 h) and remained high in the RCL, whereas the WCL responded more slowly to the MeJA treatment. Secondary metabolic products continued to rise gradually after 6 h of treatment and then dramatically increased, to levels 12-fold greater than those of the untreated control, until 72 h after treatment in the WCL. Because shikonin and shikonofuran are generated through a common pathway and are derived from the same GHQ precursor, these different responses likely involve a metabolic flux increase, relocation or redirection from GHQ towards different metabolic end products. Culture experiments also demonstrated that MeJA caused a rapid and massive increase in the expression of 5 important genes involved in shikonin biosynthesis and shikonofuran derivative formation in the WCL. Transcripts of HMGR, GDPS, C4H, 4CL and PGT were rapidly induced within 4 h, peaked within 24 h, and then decreased over time. These findings suggest that MeJA promoted the formation of shikonofuran derivatives, but not shikonin derivatives, via direct stimulation of the transcription of the shikonin biosynthetic genes.