title: The Arabidopsis cinnamoyl CoA reductase irx4 mutant has a delayed but coherent (normal) program of lignification.
abstract: Previous studies have indicated that the Arabidopsis thalianairregular xylem 4 (irx4) mutant is severely lignin-deficient, forming abnormal lignin from aberrant monomers. Studies of lignin structure in dwarfed cinnamoyl CoA reductase (CCR)-downregulated tobacco were also previously reported to incorporate feruloyl tyramine derivatives. The lignin in the Arabidopsis irx4 mutant was re-investigated at 6 weeks and at maturation (9 weeks). Application of (1)H, (13)C, 2D Heteronuclear Multiple Quantum Coherence and 2D Heteronuclear Multiple Bond Coherence spectroscopic analyses to the lignin-enriched isolates from both Arabidopsis wild-type (Ler) and the CCR-irx4 mutant at both developmental stages revealed that only typical guaiacyl/syringyl lignins were formed. For the irx4 mutant, the syringyl content at 6 weeks growth was lower, in accordance with a delayed but coherent program of lignification. At maturation, however, the syringyl/guaiacyl ratio of the irx4 mutant approached that of wild-type. There was no evidence for feruloyl tyramines, or homologues thereof, accumulating as a chemical signature in lignins resulting from CCR mutation. Nor were there any noticeable increases in other phenolic components, such as hydroxycinnamic acids. These findings were further confirmed by application of thioacidolysis, alkaline nitrobenzene oxidation and acetyl bromide analyses. Moreover, in the case of CCR downregulation in tobacco, there were no NMR spectroscopic correlations that demonstrated feruloyl tyramines being incorporated into the lignin biopolymers. This study thus found no evidence that abnormal lignin formation occurs when CCR activity is modulated.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: Dhrubojyoti D
authors.initials: DD
authors.lastname: Laskar
authors.forename: Michaël
authors.initials: M
authors.lastname: Jourdes
authors.forename: Ann M
authors.initials: AM
authors.lastname: Patten
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Helms
authors.forename: Laurence B
authors.initials: LB
authors.lastname: Davin
authors.forename: Norman G
authors.initials: NG
authors.lastname: Lewis
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008031:Lignin / Q000378:metabolism*; D009154:Mutation
chemical_list: D008031:Lignin; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase