†These authors contributed equally to this work.
Multi-site genetic modulation of monolignol biosynthesis suggests new routes for formation of syringyl lignin and wall-bound ferulic acid in alfalfa (Medicago sativa L.)
Article first published online: 30 AUG 2006
The Plant Journal
Volume 48, Issue 1, pages 113–124, October 2006
How to Cite
Chen, F., Srinivasa Reddy, M. S., Temple, S., Jackson, L., Shadle, G. and Dixon, R. A. (2006), Multi-site genetic modulation of monolignol biosynthesis suggests new routes for formation of syringyl lignin and wall-bound ferulic acid in alfalfa (Medicago sativa L.). The Plant Journal, 48: 113–124. doi: 10.1111/j.1365-313X.2006.02857.x
- Issue published online: 30 AUG 2006
- Article first published online: 30 AUG 2006
- Received 5 April 2006; revised 17 June 2006; accepted 21 June 2006.
- cell wall phenolics;
- genetic modification;
- transgenic alfalfa
Genes encoding seven enzymes of the monolignol pathway were independently downregulated in alfalfa (Medicago sativa) using antisense and/or RNA interference. In each case, total flux into lignin was reduced, with the largest effects arising from the downregulation of earlier enzymes in the pathway. The downregulation of l-phenylalanine ammonia-lyase, 4-coumarate 3-hydroxylase, hydroxycinnamoyl CoA quinate/shikimate hydroxycinnamoyl transferase, ferulate 5-hydroxylase or caffeic acid 3-O-methyltransferase resulted in compositional changes in lignin and wall-bound hydroxycinnamic acids consistent with the current models of the monolignol pathway. However, downregulating caffeoyl CoA 3-O-methyltransferase neither reduced syringyl (S) lignin units nor wall-bound ferulate, inconsistent with a role for this enzyme in 3-O-methylation ofS monolignol precursors and hydroxycinnamic acids. Paradoxically, lignin composition differed in plants downregulated in either cinnamate 4-hydroxylase or phenylalanine ammonia-lyase. No changes in the levels of acylated flavonoids were observed in the various transgenic lines. The current model for monolignol and ferulate biosynthesis appears to be an over-simplification, at least in alfalfa, and additional enzymes may be needed for the 3-O-methylation reactions of S lignin and ferulate biosynthesis.