Biology Reference
In-Depth Information
using lignocellulosic feedstock as a bioenergy and biorefinery resource that
may, at least in part, reduce our reliance on fossil fuels without interfering
largely with food production has sparked tremendous interest. Lignin has
been identified as the major hindrance in using lignocellulosic plant material
for fermentation to ethanol but is valued as a high calorimetric input in other
bioenergy technologies such as fast pyrolysis (
Weng et al., 2008c, Zhou et al.,
2011
). In either way, lignin has a major impact and targeted manipulation of
lignin quantity and composition by transgenic means has already been shown
to be efficient in changing cell wall properties that accommodate easier
digestibility. However, societal resilience towards transgenic approaches in
particular in 'green' solutions clearly hampers their use. In addition, pertur-
bations of the monolignol pathway interfere also with the production of the
plethora of non-lignin natural products derived from the phenylpropanoid
pathway, which have pivotal functions in chemical ecology that are in large
still poorly understood. Many of the studies cited above have shown that
precursors are rechannelled into other branches of the phenylpropanoid path-
way, but economically most importantly, a severe impact on plant morpholo-
gy has been observed when the monolignol pathway is severely compromised.
This includes anatomical changes that could be directly explained by the
alteration in the secondary cell wall, such as collapsed xylem vessels (e.g.
Coleman et al., 2008; Franke et al.,2002b
). More extremely, severe impair-
ments of early steps in the phenylpropanoid pathway generally cause a stark
impact on plant development resulting in extremely dwarfed phenotypes as
exemplified by the C4H-andC3
0
H-null mutants (
Abdulrazzak et al.,2006;
Schilmiller et al. 2009
). These phenotypes go beyond the expectations caused
by interference with lignin alone and may suggest the existence of a yet to be
identified hormone-like factor derived from the phenylpropanoid pathway.
REFERENCES
Abdulrazzak, N., Pollet, B., Ehlting, J., Larsen, K., Asnaghi, C., Ronseau, S.,
Proux, C., Erhardt, M., Seltzer, V., Renou, J.-P., Ullmann, P., Rauly, M.
et al. (2006). A coumaroyl-ester-3-hydroxylase insertion mutant reveals
the existence of nonredundant meta-hydroxylation pathways and essential
roles for phenolic precursors in cell expansion and plant growth. Plant
Physiology
140
, 30-48.
Achnine, L., Blancaflor, E. B., Rasmussen, S. and Dixon, R. A. (2004). Colocalization
of L-phenylalanine ammonialyase and cinnamate 4-hydroxylase for meta-
bolic channeling in phenylpropanoid biosynthesis. The Plant Cell
16
,
3098-3109.
Allina, S. M., Pri-Hadash, A., Theilmann, D. A., Ellis, B. E. and Douglas, C. J.
(1998). 4-Coumarate:coenzyme A ligase in hybrid poplar. Properties of
