Biology Reference
In-Depth Information
AtMYB63) and up-regulation of AtNST1 leads to up-regulation of both
AtMYB58 and AtMYB63. These results clearly indicate that NAC factors
play an important role in regulating lignin biosynthesis. More recently, certain
NAC factors have been shown to directly regulate the expression of poplar
laccases homologs of AtLAC4 and AtLAC11 (
Ohtani et al.,2011
). Subsequent
transient activation assays revealed that 10/12 PtVNS/PtWND (P. trichocarpa
VND-, NST/SND-, SMB-related proteins/P. trichocarpa wood associated
NAC domain TFs) genes are able to activate the poplar ortholog of
AtLAC11. The capacity of the PtVNS/PtWND genes to activate the poplar
AtLAC4 gene was not evaluated in this study. Interestingly, certain PtVNS/
PtWND genes activated both the poplar laccases gene as well as a cationic
peroxidase gene. Expression profiling in flax (Huis et al., unpublished) has also
shown that an ortholog of the arabidopsis NAC protein ANAC002/ATAF1
is co-regulated with 2 PAL unigenes and the flax orthologs of AtLAC4 and
AtLAC17 suggesting that the regulation of both monolignols production and
oxidative polymerization in flax involve NAC TFs.
In silico analyses of arabidopsis laccases promoters (
Turlapati et al.,2011
)
reveals that all promoters, except for AtLAC6 and AtLAC14 genes, contain
copper-response elements suggesting that laccases gene expression in plants
is regulated by copper levels. Copper can activate gene expression in plants
through either oxidative stress- or metal-mediated mechanisms leading to
activation of MAPK signalling pathways induced stress (
Jakubowicz et al.,
2010
). Several studies have shown that the addition of copper to the culture
medium increases laccases transcript levels in lignin-degrading fungi
(
Canessa et al., 2008; Galhaup et al., 2002
). More detailed studies indicated
that the copper ion was recruited by an ACE (activation of cup1) TF and that
the metallic ion is necessary for DNA binding by stabilization of the protein
tertiary structure (
Canessa et al.,2008
). A link between copper and laccases
gene expression is also supported by the observation that the expression of
genes involved in copper metabolism (and water stress) is affected in the
laccases Atlac4, Atlac7 double mutant (
Berthet et al., 2011
).
Copper has also been shown to play a central role in regulating the expres-
sion of different laccases genes in arabidopsis through a post-transcriptional
mechanism implicating different microRNAs (miRNAs) (
Abdel-Ghany
and Pilon, 2008
). miRNAs are endogenous small non-coding RNAs involved
in regulating gene expression at the post-transcriptional level (
Axtell et al.,
2007
).
After processing, a miRNA-AGO1 (Argonaute 1) complex associates
with its mRNA target and blocks gene expression by cleaving mRNA or
repressing translation (
Baumberger and Baulcombe, 2005
). Gene target
specificity is determined by the nucleotide sequence of the miRNA that is
complementary to a sequence in the mRNA. A miRNA (miR398) was
