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over-expressing F5H genes, but unfortunately, this objective was misled at
the start by the promising results obtained on 4CL-downregulated green-
house-grown poplar trees, that were not subsequently confirmed in the field
( Hu et al., 1999 ). From our present knowledge, we can propose that both
downregulation of C4H or CAD and over-expression of F5H using xylem-
specific promoters would be a promising combination for investigation in
transgenic trees.
C. NEED FOR AMBITIOUS PLANS FOR EXPERIMENTAL FIELD TRIALS
TO IDENTIFY EFFICIENT INNOVATIVE BIOTECH TREES
Finally, it is important to emphasize that performing field test trials, in
multisites and with a large number of genetically modified tree lines, are
important requirements for the selection of innovative trees.
As illustrated in the first section, most of the studies on lignin-modified
trees were, however, performed in controlled and often optimal growth
conditions, mainly in greenhouses. Even when more than 700 field trials of
GM trees were reported from a search of publicly accessible databases
( Walter et al. 2010 ), field trial studies were carried out only for a small subset
of lignin-modified transgenic trees and most often on a single site. This is
probably for the following reasons:
(i). For a number of transgenic trees, the effects of modifications were strong
enough to give early visible deleterious effects on tree growth and devel-
opment, even when grown in favourable greenhouse conditions.
(ii). The majority of these studies were carried out in University laboratories
with no expertise, no possibility or even no aim of setting up a field trial,
while the majority of the field trials have been set up by a very small
number of public institutions or private companies. Generally, only the
data generated by the former are publicly available.
(iii). For the remaining studies, only a small number of field trials, most often
small scale and on a single location, have been set up. This is at least
partly due to the burden of efforts and costs to comply with regulations
enforced for the dissemination of GMO in field trials ( Viswanath et al.,
2012 ). Indeed, setting a field trial with transgenic plants also requires a
major effort to advertise at different levels on the interests of performing
such studies, often in front of a part of society hostile to such dissemina-
tion experiments. Sometimes, GM opponents have organized the
destruction of transgenic field trials and consequently, the early termina-
tion of these labour-intensive experiments: regarding transgenic trees,
this unacceptable turn of events has occurred mostly in Europe, in 1999
in Jealott's Hill (England) for lignin-modified poplars or in 2004 in
Punkaharju (Finland) for sterility in birch.
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