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Exploring lignification in conifers by silencing hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase in Pinus radiata. | LitMetric

AI Article Synopsis

  • The enzyme hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (HCT) is crucial for producing lignin precursors in flowering plants, and a similar gene was found in the conifer Pinus radiata.
  • The cloned HCT gene in P. radiata was shown to be active during tracheary element formation and shared a significant sequence similarity with the HCT from tobacco.
  • Silencing this gene resulted in a notable reduction in lignin content and changes in its composition, indicating that HCT plays a key role in lignin biosynthesis in both angiosperms and P. radiata.

Article Abstract

The enzyme hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (HCT) is involved in the production of methoxylated monolignols that are precursors to guaiacyl and syringyl lignin in angiosperm species. We identified and cloned a putative HCT gene from Pinus radiata, a coniferous gymnosperm that does not produce syringyl lignin. This gene was up-regulated during tracheary element (TE) formation in P. radiata cell cultures and showed 72.6% identity to the amino acid sequence of the Nicotiana tabacum HCT isolated earlier. RNAi-mediated silencing of the putative HCT gene had a strong impact on lignin content, monolignol composition, and interunit linkage distribution. AcBr assays revealed an up to 42% reduction in lignin content in TEs. Pyrolysis-GC/MS, thioacidolysis, and NMR detected substantial changes in lignin composition. Most notable was the rise of p-hydroxyphenyl units released by thioacidolysis, which increased from trace amounts in WT controls to up to 31% in transgenics. Two-dimensional 13C-1H correlative NMR confirmed the increase in p-hydroxyphenyl units in the transgenics and revealed structural differences, including an increase in resinols, a reduction in dibenzodioxocins, and the presence of glycerol end groups. The observed modifications in silenced transgenics validate the targeted gene as being associated with lignin biosynthesis in P. radiata and thus likely to encode HCT. This enzyme therefore represents the metabolic entry point leading to the biosynthesis of methoxylated phenylpropanoids in angiosperm species and coniferous gymnosperms such as P. radiata.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913891PMC
http://dx.doi.org/10.1073/pnas.0701428104DOI Listing

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