Biology Reference
In-Depth Information
arabidopsis (
Arabidopsis Genome Initiative, 2000
), poplar (
Tuskan et al.,
2006
), maize (
Schnable et al., 2009
), and recently brachypodium (
Vogel et al.,
2010
), as well as the availability of mutant collections for plant models
(
Bechtold et al., 1993
;
Alonso et al., 2003 for Arabidopsis; Vain et al., 2008
for Brachypodium), or the improved technologies for specifically silencing
specific target genes (for review, see
Matthew, 2004
). The plant model Ara-
bidopsis thaliana, a small-lignified dicotyledonous species with a short gener-
ation time, has proved to be highly relevant for lignification studies
(
Vanholme et al., 2010
). In addition, the arabidopsis gene expression data-
bases (
https://genevestigator.com
;
Zimmermann et al., 2004
;
http://genecat.
mpg.de
;
Mutwil et al., 2008
) provide important information on the spatio-
temporal expression patterns of genes. Such information has proved to be
particularly useful for selecting the best gene candidates from multigenic
families including plant laccases genes (
Berthet, 2010; Berthet et al., 2011
).
More recently, a database specific for laccases and other multicopper oxi-
dases was developed for improved sequence-based classification
http://www.
lcced.uni-stuttgart.de
(
Sirim et al., 2011
).
A. FIRST LITERATURE DATA FOR OR AGAINST LIGNIN-SPECIFIC LACCASES
The dehydrogenative polymerization of monolignols into lignins was pro-
posed as early as the 1930s (
Erdtman, 1933; Freudenberg and Nelsh, 1968
)
and both the main plant oxidases—laccases and peroxidases—were sug-
gested to enzymatically support monolignol coupling. Although both laccases
and peroxidase activities were reported in the differentiating xylem of spruce
(as reviewed in
Freudenberg and Nelsh, 1968
), two different studies led to the
conclusion that laccases were not involved in lignification. The laccases
purified from Rhus vernicifera could not oxidize coniferyl alcohol to synthetic
lignin in vitro (
Nakamura, 1967
) and no laccases activity could be histochem-
ically detected in lignifying tissues of green ash (
Harkin and Obst, 1973
). As a
result the potential role of laccases to assist peroxidases in lignification was
neglected for a long time and it was not until the 1990s that the results of
several studies suggested that laccases might indeed be involved in the
lignification process. In the absence of H
2
O
2
, a laccases purified from syca-
more maple (Acer pseudoplatanus) cell culture could catalyse the in vitro
polymerization of monolignols (
Driouich et al., 1992; Sterjiades et al.,
1992
). Another study also described laccases activity in loblolly pine (Pinus
taeda) xylem (
Bao et al., 1993
).
Sterjiades et al. (1993)
suggested that laccases
may function during the early stage of lignification to polymerize mono-
lignols, whereas peroxidases may function during later stages of xylem
development. In poplar, two laccases isolated from xylem were capable to
