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used to characterize the developmental- and wound-induced expression pro-
files of the four 4CL genes (At4CL1-At4CL4)inArabidopsis (
Soltani et al.,
2006
). The semi-quantitative RT-PCR revealed that the four genes responded
differently to wounding of leaves of 3-4-week-old plants. At4CL1 and At4CL2
expression increased 2.5 h post-wounding before falling to basal levels at 12 h
and then increasing again to a maximum between 48 and 72 h. At4CL4
expression also increased at 2.5 h post-wounding and remained elevated for
12 h before declining. Finally, At4CL3 decreased following wounding before
returning to basal levels at 4 h post-wounding and then gradually increasing to
72 h. The genes At4CL1 and At4CL2 are believed to be the 4CL genes
associated with lignification, while At4CL3 is more likely associated with
flavonoid biosynthesis. At4CL4 is expressed throughout seedling roots.
Promoter-GUS histochemical staining showed that the At4CL4 promoter
is rapidly activated (within minutes) following wounding whereas At4CL3 is
not activated. At4CL1 and At4CL2 are activated, but only after 72 h post-
wounding. Taken together, these results suggest that At4CL4 is involved
in the early wound response in Arabidopsis leaves. Promoter deletions indi-
cated the presence of both positive and negative regulatory elements as
well as suggesting the existence of an intron regulatory element. However,
although this work provided detailed information on the expression profiles
of the 4CL gene family in Arabidopsis, it did not examine whether wounding
induced lignification and it is possible that 4CL gene expression might be
associated with the production of secondary metabolites.
In support of this hypothesis, a recent study (
Deflorio et al., 2011
)ofthe
effect of wounding on phenylpropanoid gene expression in Sitka spruce
indicated differences in the response of bark and sapwood to wounding.
Trees were wounded by drilling, and samples from both the wound zone
and at 1 cm distant from the wound zone were analysed 3 days post-wounding.
Quantitative RT-PCR indicated that, in bark tissues, the expression of PAL,
CCR, HCT and PX3 (peroxidase) increased. In contrast, CAD gene expres-
sion decreased. In sapwood samples, the expressions of PAL, CCR, HCT
and CAD either decreased or did not change. The expression of the PX3 gene
increased. Analyses of lignin content (thioglycolic acid assay) showed that
wounding did not induce a significant increase in lignin content in either bark
or sapwood samples 3 days after wounding. In contrast, HPLC analyses
showed that combined wounding and fungal inoculation (wounding alone
was
not tested) induced a significant increase in the amounts of certain
phenolics (coniferin, astringin, taxifolin, piceid, isorhapontin) in the cell
wall-bound fraction (but not the soluble fraction) in bark samples, but not
sapwood samples. These results suggest that the modifications in phenylpro-
panoid gene expression levels are associated with the production of a wide
