|Alchanati, Iris - TEXAS A&M UNIVERSITY|
|Patel, Jo Ann - TEXAS A&M UNIVERSITY|
|Benedict, Chauncey - TEXAS A&M UNIVERSITY|
|Cui, Yunxing - TEXAS A&M UNIVERSITY|
|Magill, Clint - TEXAS A&M UNIVERSITY|
Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 1997
Publication Date: N/A
Interpretive Summary: In cotton a compound called delta-cadinene is the biosynthetic precursor to a large number of compounds that are important in protecting the plant from diseases and insects. The mechanism by which delta-cadinene is formed and its role in defending the plant against pathogens is only partially known. We have shown that delta-cadinene is formed from nerolidyl diphosphate. When the plant is infected with a pathogen, we showed that the messenger RNA controlling the synthesis of delta-cadinene appears prior to that of the compounds which protect the plant. This information further explains the biosynthesis of these important compounds and supports our findings that these compounds are important in protecting the cotton plant from diseases.
Technical Abstract: Soluble preparations of cotton stele tissue infected with Verticillium dahliae containing delta-cadinene synthase converts (1-RS)-[1-2H]-E,E- farnesyl diphosphate to [5-2H]- and [11-2H]-delta-cadinene and converts [4,4,13,13,13-2H5]-nerolidyl diphosphate to [8,8,15,15,15-2H5]- delta-cadinene. These data imply that nerolidyl diphosphate (NDP) is an intermediate in the enzymatic cyclization of the natural substrate E,E-farnesyl diphosphate (E,E-FDP) to delta-cadinene by delta-cadinene synthase and involves the conversion of E,E-FDP to NDP followed by cyclization to cis-germacradienyl cation, a 1,3-hydride shift, a second cyclization to a cadinanyl cation and deprotonation to delta-cadinene. Kinetic analyses of induced delta-cadinene synthase mRNA, delta-cadinene synthase activity and formation of sesquiterpenoid phytoalexins in cotton stele tissue infected with Verticillium dahliae show that 12 hrs after the fungal inoculation the delta-cadinene synthase mRNA was at a peak level. The tissue injected with H2O in place of the fungal inoculation showed no detectable delta-cadinene synthase mRNA or delta-cadinene synthase activity after 12 to 96 hrs. After 12 hrs, 54% of the delta-cadinene synthase activity had developed, but no phytoalexins were detected. These data, together with the enzyme analyses, support the conclusion that V. dahliae initiates a signal in the stele tissue that results in an increased steady-state level of delta-cadinene synthase mRNA and an increased activity of delta-cadinene synthase which functions in the conversion of E,E-FDP to NDP to delta-cadinene that is metabolically converted to desoxyhemigossypol, desoxyhemigossypol-6-methyl ether, hemigossypol and hemigossypol-6-methyl ether.