|Stipanovic, Robert - Bob|
Submitted to: Genetic Control of Cotton Fiber and Seed Quality Workshop
Publication Type: Proceedings
Publication Acceptance Date: 12/5/2000
Publication Date: N/A
Technical Abstract: The first step in the conversion of the isoprenoid intermediate farnesyl diphosphate (FDP) to sesquiterpene phytoalexins in cotton plants is catalyzed by delta-cadinene (CDN) synthase. The enzyme cyclizes (1-RS)- [1-2H]-(E,E)-FDP to a single product that GC-MS analysis show is a mixture of [5-2H]- and [11-2H]-CDN. The specifically labeled CDN can be accounted for by the cyclization of FDP to a cis-germacradienyl cation, a 1,3- hydride shift, a second cyclization to a cadinanyl cation followed by a deprontonation to CDN. The conversion of CDN to desoxyhemigossypol (dHG) and hemigossypol(HG) by the infusion of 3H-CDN in intact cotton cotyledons has been demonstrated. The bimolecular naphthoxy radical coupling of HG to gossypol (G) catalyzed by a peroxidase present in developing cottonseed has been demonstrated. The above studies support a G pathway for the biosynthesis of G from FDP as: FDP to nerolidyl-PP (NDP) to CDN to dHG to HG to G. The CDN synthase catalyses the first step of the G pathway at a branch point in the general pathway for the synthesis of plant isoprenoids and is an attractive target for regulating G in cottonseed. In 38 day-old developing cottonseed CDN synthase activity and G formation reached peak values. Northern blots showed that CDN synthase mRNA transcripts reached steady state levels in 30 to 36 day-old developing seed. Collectively these studies demonstrate that CDN synthase activity, dHG, HG and G formation are dependent on the expression of cdn synthase and that an antisense cdn synthase may regulate G formation in cottonseed.