|Benedict, C - TEXAS A&M UNIVERSITY|
|Alchanati, Iris - TEXAS A&M UNIVERSITY|
Submitted to: Biochemistry of Cotton Workshop
Publication Type: Proceedings
Publication Acceptance Date: September 24, 1994
Publication Date: N/A
Technical Abstract: Cotton plants respond to infection by Verticillium dahliae by synthesizing a cadalene group of phytoalexins: desoxyhemigossypol (dHG), desoxyhemigossypol-6-methyl ether (dMHG), hemigossypol (HG), hemigossypol-6-methyl ether (MHG) and gossypol (G). We have isolated a volatile hydrocarbon radiolabelled from [1-3H]-(E,E)-farnesyl diphosphate (FDP) in homogenates of cotton stele tissue infected with V. dahliae which may be a precursor of dHG and HG. For identification the hydrocarbon was enzymatically labelled from (1RS)-[1-2H]-(E,E)-FDP and analyzed by GC-MS. Its mass spectrum agrees with that of delta-cadinene and demonstrates that [5-2H]-delta-cadinene is formed from (1R)-[1-2H]-(E,E)-FDP and that [11-2H]-delta-cadinene is formed from (1S)-[1-2H]-(E,E)-FDP by a delta-cadinene synthase by a proposed mechanism consisting of the isomerization of the E,E-FDP to nerolidyl diphosphate followed by cyclization to a cis-germacradienyl cation and a 1,3-hydride shift, a second cyclization and deprotonation to a delta-cadinene. Delta-cadinene is the putative precursor to dHG, HG and G. Since delta-cadinene synthase catalyzes the first step in G formation from FDP at a branch point in the common isoprenoid pathway, the identification of the delta-cadinene synthase gene offers the long-range possibility of controlling G formation in cottonseed by antisense technology.