title: Molecular and biochemical basis for stress-induced accumulation of free and bound p-coumaraldehyde in cucumber.
abstract: To elucidate the genetic and biochemical regulation of elicitor-induced p-coumaraldehyde accumulation in plants, we undertook a multifaceted approach to characterize the metabolic flux through the phenylpropanoid pathway via the characterization and chemical analysis of the metabolites in the p-coumaryl, coniferyl, and sinapyl alcohol branches of this pathway. Here, we report the identification and characterization of four cinnamyl alcohol dehydrogenases (CADs) from cucumber (Cucumis sativus) with low activity toward p-coumaraldehyde yet exhibiting significant activity toward other phenylpropanoid hydroxycinnamaldehydes. As part of this analysis, we identified and characterized the activity of a hydroxycinnamoyl-coenzyme A:shikimate hydroxycinnamoyl transferase (HCT) capable of utilizing shikimate and p-coumaroyl-coenzyme A to generate p-coumaroyl shikimate. Following pectinase treatment of cucumber, we observed the rapid accumulation of p-coumaraldehyde, likely the result of low aldehyde reductase activity (i.e. alcohol dehydrogenase in the reverse reaction) of CsCAD enzymes on p-coumaraldehyde. In parallel, we noted a concomitant reduction in the activity of CsHCT. Taken together, our findings support the hypothesis that the up-regulation of the phenylpropanoid pathway upon abiotic stress greatly enhances the overall p-coumaryl alcohol branch of the pathway. The data presented here point to a role for CsHCT (as well as, presumably, p-coumarate 3-hydroxylase) as a control point in the regulation of the coniferyl and sinapyl alcohol branches of this pathway. This mechanism represents a potentially evolutionarily conserved process to efficiently and quickly respond to biotic and abiotic stresses in cucurbit plants, resulting in the rapid lignification of affected tissues.
authors.affiliation: Department of Plant Pathology, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Marina
authors.initials: M
authors.lastname: Varbanova
authors.forename: Katie
authors.initials: K
authors.lastname: Porter
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Ray
authors.initials: R
authors.lastname: Hammerschmidt
authors.forename: A Daniel
authors.initials: AD
authors.lastname: Jones
authors.forename: Brad
authors.initials: B
authors.lastname: Day
mesh_terms: D000217:Acyltransferases / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000447:Aldehydes / Q000378:metabolism*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology; D002934:Cinnamates / Q000378:metabolism*; D018553:Cucumis sativus / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018546:Hypocotyl / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008031:Lignin / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000187:drug effects; D011096:Polygalacturonase / Q000494:pharmacology; D020005:Propanols / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D000447:Aldehydes; D002934:Cinnamates; D020005:Propanols; D012333:RNA, Messenger; C117045:p-hydroxycinnamaldehyde; C439395:1-phenylpropanol; D008031:Lignin; D000429:Alcohol Oxidoreductases; C018656:cinnamyl alcohol dehydrogenase; D000217:Acyltransferases; D011096:Polygalacturonase