Hinokinin biosynthesis in Linum corymbulosum Reichenb

We established that the biologically active lignan (-)-hinokinin could be isolated from in vitro cultures of Linum corymbulosum. Two hypothetical pathways were outlined for the biosynthesis of (-)-hinokinin. In both pathways (+)-pinoresinol serves as the primary substrate. In the first pathway pinoresinol is reduced via lariciresinol to secoisolariciresinol by a pinoresinol-lariciresinol reductase and the methylenedioxy bridges are formed later. In the second pathway pinoresinol itself is the substrate for the formation of the methylenedioxy bridges resulting in the consecutive production of piperitol and sesamin. We isolated several cDNAs encoding one pinoresinol-lariciresinol reductase (PLR-Lc1), two phenylcoumaran benzylic ether reductases (PCBER-Lc1 and PCBER-Lc2) and two PCBER-like proteins from a cDNA library of L. corymbulosum. PLR-Lc1 was found to be enantiospecific for the conversion of (+)-pinoresinol to (-)-secoisolariciresinol, which can be further converted to (-)-hinokinin. Hairy root lines with significantly reduced expression levels of the plr-Lc1 gene were established using RNAi technology. Hinokinin accumulation was reduced to undetectable levels in these lines. Our results strongly indicate that PLR-Lc1 participates in (-)-hinokinin biosynthesis in L. corymbulosum by the first of the two hypothetical pathways.

Acknowledgements: We thank the Yildiz Technical University and the Turkish Higher Education Council for financial support to Ürün Bayindir. Furter financial support from the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

References: 1. Mohagheghzadeh, A. et al. (2006) Planta Med. 72: 1165–1167. 2. Bayindir, Ü. et al. submitted