Biology Reference
In-Depth Information
M. DOF DOMAIN TRANSCRIPTION FACTORS
The sequence of a DOF (DNA binding with one finger) domain transcription
factor (named WALLDOF) with a cambium-preferred expression profile was
introduced into poplar under the control of a C4H xylem-specific promoter
(
Gerhardt et al., 2011
). Two-month-old transgenic poplar plants were
screened for changes in lignin deposition. Over-expression of WALLDOF
in transgenic poplar led to a dramatic thickening of secondary walls and a
reduction in the lumen area. This wall thickening resulted in higher wood
density, increased cellulose content, reduction in hemicellulose carbohy-
drates, mainly mannose and arabinose and alterations in lignin composition.
N. UDP-GLUCOSE PYROPHOSPHORYLASE
The modification of genes apparently not involved in lignification translated
sometimes in strong effects on lignification. This was the case when a bacterial
UDP-glucose pyrophosphorylase was over-expressed in transgenic poplar in
order to increase cellulose production and content. In effect, in 4-month-old
transgenic poplars, the genetic modification induced important pleiotropic
effects linked to alterations in C allocation and resulting in impaired growth
and development, with reduced growth height and stem diameter, elongated
axial shoots and smaller leaves. Further analysis performed on the transgenic
poplar plants revealed an increased polysaccharide content, including cellu-
lose, a concurrent decrease in lignin content, increased S/G ratio and also a
dramatic increase in salicylic acid 2-O-
-D glucoside probably associated with
plant responses to the stress associated with the genetic modification (
Coleman
et al., 2007
). However, it should be pointed out that the change in lignin
content was only the consequence of an increased proportion of cellulose in
the cell wall. The explanation for the increased S/G ratio that was linked to an
increase in F5H transcript abundance is not so straightforward.
b
O. SYNTHETIC TYROSINE RICH PEPTIDE GENE
This pioneer study is based on the hypothesis that the free radical coupling
between monolignol subunits and tyrosine will result in a lignin structure
that can be easily hydrolysed with proteases (
Liang et al., 2008
). Toward
this end, parsley tyrosine-rich hydroxyproline-rich coding sequence glyco-
protein gene was fused to a leader sequence derived from a lodgepole pine
xylem
-glucosidase cDNA and the poplar PAL2 promoter to address
transgene production to the cell wall during lignification. Greenhouse-
grown transgenic poplar (cv. Ogy P. deltoides
b
P. nigra) plants did not
show abnormal growth and development, stem structure and lignin
