Biology Reference
In-Depth Information
Agrobacterium-mediated cotransformation system, introduced into the same
tree both antisense poplar 4CL and sense sweetgum F5H under the control of
the xylem-specific promoter pPt4CL1. Ten-month-old greenhouse-grown dou-
ble-transformant plants did indeed exhibit both a strong reduction in lignin
content reminiscent of 4CL downregulation and a strong increase in S unit,
characteristics of F5H over-expression. Further evaluation of these modified
trees under field conditions found, however, alterations in growth and develop-
ment as observed in 4CL single transformants. Additive results were also
obtained for ASCAD
ASCOMT double-transformed poplars (
Lapierre
et al., 1999
). Interestingly, certain other combinations did not yield additive
results: this was the case of COMT
CCoAOMT double transformants which
were unable to develop in field conditions and died during the first winter
season after plantation, whereas single transformant trees planted alongside
developed similarly to control trees (G. Pilate, J.C. Lepl
ยด
, W. Boerjan, unpub-
lished results).
Several attempts have been made to induce the production of S units in a
conifer. Toward this end, a large number of larch transgenic lines transformed
with a construct carrying a poplar COMT gene in the sense orientation under
the control of the pCaMV 35S constitutive promoter were produced. Howev-
er, transgenic larch stems with strong heterologous OMT activity did not
exhibit any strong changes in lignin composition (
Pilate et al., 1999
).
Further, a poplar F5H gene under the control of the double pCaMV 35S
promoter was introduced into a COMT over-expressing transgenic larch line,
but the resulting transformed lines did not reveal the appearance of any S unit
incorporated in the lignin of transgenic plants (
Gatineau et al., 2001
). This led
to the conclusion that the introduction of these two enzymes was not sufficient
to induce S unit production and incorporation in a conifer background.
Besides genes coding enzymes from the monolignol pathway, several other
GM trees have been shown to be affected with differing degrees in their lignin
content or composition.
L. LIM DOMAIN TRANSCRIPTION FACTORS
Eucalyptus (E. camaldulensis) plants were transformed with an antisense copy
of a LIMdomain transcription factor gene from eucalyptus (EcLIM1) involved
in the regulation of lignin biosynthesis under the control of the CaMV 35S
promoter. Suppression of EcLIM1 expression in 10-month-old greenhouse-
grown transgenic plants resulted in a coordinated decrease in the expression
levels of several lignin biosynthesis genes, namely those coding for PAL, C4H
and 4CL, resulting, in the most altered plants, in a 29% reduction of lignin
content. The most affected plants presented altered growth with premature leaf
loss possibly due to alterations in water transport ability (
Kawaoka et al., 2006
).
