Molecular and Biochemical Basis for Stress-Induced Accumulation of Free and Boundp-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.

Expression of a bacterial 3‐dehydroshikimate dehydratase reduces lignin content and improves biomass saccharification efficiency

“…A low lignin content rich in H units and higher S/G corresponds to a phenotype previously characterized in plants down‐regulated for hydroxycinnamoyl‐CoA shikimate/quinate hydroxycinnamoyl transferase (HCT), p ‐coumarate 3‐hydroxylase (C3H) or caffeoyl shikimate esterase (CSE) (Ralph et al ., ; Vanholme et al ., ; Ziebell et al ., ). Moreover, reduction of HCT activity results in the accumulation of free and bound p ‐coumaraldehyde in cucumber and of p ‐coumarate in alfalfa, presumably due to the build‐up of coumaroyl‐CoA (Gallego‐Giraldo et al ., ; Varbanova et al ., ). This suggests that an alteration of these biosynthetic steps has occurred in the C4H::qsuB lines.…”

Cellular and Genetic Regulation of Coniferaldehyde Incorporation in Lignin of Herbaceous and Woody Plants by Quantitative Wiesner Staining

“…Although the Wiesner test has been widely used for 140 years, its target(s) and efficiency remain uncertain as it does not reflect total lignin amount (Black et al, 1953) or aldehyde residues in lignin (Adler and Ellmer, 1948;Kim et al, 2002). However, many lignin monomers have been shown to react positively to the Wiesner test such as G C 6 C 3 aldehyde (coniferaldehyde), S C 6 C 3 a l d e h y d e ( s i n a p a l d e h y d e ) , H C 6 C 3 a l d e h y d e ( pcoumaraldehyde), G C 6 C 3 without function (eugenol), and G C 6 C 3 alcohol (coniferyl alcohol) as well as various G and S C 6 C 1 aldehydes (Adler and Ellmer, 1948;Black et al, 1953;Ishikawa and Ide, 1954;Bland, 1966;Geiger and Fuggerer, 1979;Pomar et al, 2002;Kim et al, 2002;Varbanova et al, 2011). To solve this conundrum and determine the exact target(s) and chemical reaction behind the Wiesner test, monomer analogues were used to monitor the production of chromophore(s), their structure and stability as well as their absorbance.…”

Global dissection of the BAHD acyltransferase gene family in soybean: Expression profiling, metabolic functions, and evolution

“…Meanwhile, GmACT21, GmACT22, GmACT32, and GmACT33 fall closest with TpHCT1A/1B, which use caffeoyl or p-coumaroyl as a donor to form shikimates or malates [74] and play a major role in monolignol synthesis [29,74]. Lignin precursors are synthesised through p-coumaroyl derivatives rather than methoxylated analogues in response to pathogen attacks [80]. TpHCT activity was higher in the stem and capable of transferring p-coumaroyl moieties from the respective CoA to shikimic acid, which is critical for the biosynthesis of monolignol lignin precursors [29,74].…”