Biology Reference
In-Depth Information
apparent that the regulation of laccases gene expression controls lignification
at the oxidative polymerization step. Like many other plant genes, laccases
are regulated by different developmental and environmental cues. For exam-
ple, fungal laccases are regulated by aromatic compounds derived from
lignin degradation, by the nitrogen concentration in the culture media, by
the carbon source and by the presence of different metallic ions (
Aro et al.,
2005; Galhaup et al., 2002
).
A recent in silico analyses of arabidopsis laccases promoters identified a
number of different potential regulatory sequences (
Turlapati et al., 2011
).
All laccases promoters have potential binding sites for MYB and/or MYC
TFs, as well as ARF binding sites, and T-box promoter motifs and W-box
elements. There is a statistically significant over-representation of binding
sites for MYB4 and MYB1AT factors. Analyses also showed that six laccases
promoters (AtLAC1, AtLAC2, AtLAC4, AtLAC10, AtLAC11, AtLAC17)
contained at least one AC element characteristic of phenylpropanoid gene
promoters and known to be involved in MYB factor mediated transcription-
al regulation of these genes.
Experimental information on transcriptional regulation of laccases genes
was obtained from studies of plants up-/down-regulated for different MYB
TFs suspected to be involved in controlling lignin and secondary cell wall
biosynthesis. Comparative transcriptomics by affymetrix microarrays and
Illumina sequencing (
Ko et al., 2009
) of arabidopsis plants over-expressing
AtMYB46 indicated that ectopic secondary cell wall formation was asso-
ciated with upregulation of a large number of cellulose, hemicellulose, and
lignin biosynthetic genes suggesting that AtMYB46 is a master regulatory
gene in this process. Transcriptomic data indicated that AtLAC4 (IRX12),
AtLAC10,andAtLAC11 genes were also up-regulated and suggested that
this MYB protein also regulates the expression of laccases genes. However,
subsequent transient activation analyses revealed that AtMYB46 was incapa-
ble of directly activating AtLAC10 expression and suggested that this laccases
gene was activated indirectly via the AtMYB46-activation of another TF
gene (AtC3H14). The direct effects of AtMYB46 on AtLAC4 and AtLAC11
expression were not evaluated in this study. Dominant repression and over-
expression of two other MYB factor genes (AtMYB58 and AtMYB63)in
arabidopsis was shown to be associated with reduced lignification and ectopic
lignification, respectively (
Zhou et al.,2009
). Electrophoretic mobility shift
assays experiments showed that AtMYB58 and AtMYB63 we
re able to bind to
AC elements in the 4CL lignin gene promoter and that the AtMYB58 protein
was able to directly activate AtLAC4 but not AtLAC17. Taken together, these
results clearly suggest that laccases genes in arabidopsis are transcriptionally
regulated by MYB proteins and by other TFs.
