Biology Reference
In-Depth Information
In conclusion, it appears that laccases gene expression is coordinated with that
of monolignols biosynthesis genes and involves not only a complex regulatory
network of TFs but also copper-dependent miRNA-based mechanisms and
other post-transcriptional mechanisms.
V. CONCLUSION AND PERSPECTIVES
Laccases are widespread oxidases represented by large gene families in
plants. The definite establishment of their involvement in the polymerization
of lignins has been difficult to establish for three main reasons: (1) the broad
range of in vitro laccases substrates, which makes the identification of specific
in vivo substrate(s) difficult; (2) the broad individual expression profile of
most laccases expressed in model plants, that is, very few laccases show a
strict spatial or temporal specificity; and (3) the redundancy of gene expres-
sion patterns of different laccases, which probably underlies a functional
redundancy. As recently shown (
Turlapati et al., 2011
), deciphering the
spatial and temporal expression patterns of laccases might contribute to
elucidating their functional roles. Up to now, the physiological roles of
laccases have only been assessed via a forward genetics approach for a few
members of the 17-member arabidopsis multigene family. The seed-specific
laccases (AtLAC15/TT10) is involved in the polymerization of seed coat
flavonoids and the production of brown and insoluble polymers with a
putative protective role (
Pourcel et al., 2005
). The stem-specific laccases
AtLAC4 and AtLAC17 are definitely involved in lignification (
Berthet
et al., 2011
), with the possible assistance of AtLAC12 (this study). There
are thus many other arabidopsis laccases genes with still unknown functions.
As clearly demonstrated for the AtLAC4 and AtLAC17 genes, the most
appropriate approach to determine the function of these 14 laccases would
probably be the production of multiple mutants in order to suppress putative
functional redundancy. The recent observation showing that AtLAC17
silencing in arabidopsis mainly affects the deposition of G-lignin units in
the interfascicular fibres of stems (
Berthet et al., 2011
) provides new clues
into elucidating the precise role of this laccases that significantly and specifi-
cally contributes to lignification of supportive tissues. Nevertheless, the
spatiotemporal processes governing the lignin polymerization process seem
more mysterious than ever and the question as to why G unit deposition in
the fibres of lac17 is mainly affected still remains to be addressed.
Such specificity might be due to the spatiotemporal specificity of AtLAC17
expression or alternatively, by a higher substrate specificity of this laccases
towards coniferyl alcohol. Further investigation of the complex network of
