Biology Reference
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previously shown to down-regulate the expression of a copper/zinc superox-
ide dismutase gene in arabidopsis in response to low copper levels (
Yamasaki
et al., 2007
). Subsequent computational analysis predicted that genes encod-
ing copper-containing laccases are also targeted by three different miRNAs
(miR408, miR397, and miR857) in arabidopsis (
Abdel-Ghany and Pilon,
2008
). The miR408 is predicted to target AtLAC3, AtLAC12, and AtLAC13;
miR397a/b are predicted to target AtLAC2, AtLAC4, and AtLAC17;and
miR857 is predicted to target AtLAC7. Plants were grown in hydroponic
conditions under three different copper regimes (Cu-deficient, Cu-limited,
and Cu-replete) and expression profiles of miRNA precursors and potential
target genes were evaluated. Transcripts for miR408, miR397, and miR857
accumulate when copper is limiting and disappear when copper is sufficient.
In contrast, transcripts for target laccases genes showed a reciprocal profile,
that is, transcripts decrease when copper is limiting and accumulate when
copper is sufficient. Interaction between miRNAs and target genes was
confirmed by the identification of specific cleavage products. MicroRNAs
have also recently been shown to play a role in regulating the expression
of laccases and other genes in poplar (
Lu et al., 2011
). Another study
(
Lu et al., 2009
) has also recently underlined the potential role of RNA
degradation mechanisms in regulating laccases gene expression via the con-
trolled elimination of miRNAs.
Using the PsRNA target tool (
Dai and Zhao, 2011
), 25 poplar genes are
predicted to be putative targets for miR397a (default parameter values).
Of these predicted targets, only one gene does not encode a putative laccases
(not shown). All of the poplar genes clustering with AtLAC4 and AtLAC17,
except PtrLAC5, are predicted targets of miR397a (
Fig. 2
). As shown in
Fig. 2
, a tight correlation is observed between the expression clads, the
phylogenetic clads, and the prediction of predicted miR397a targets. As for
AtLAC4 and AtLAC17, miR397a may play an important role in the control
of poplar laccases, particularly those related to xylem formation.
Bioinformatic analyses of laccases genes have also indicated the existence of
other potential regulatory mechanisms (
Turlapati et al.,2011
). For example,
natural antisense transcripts are present at the loci for the genes AtLAC6 and
AtLAC17.Thesecis-antisense strands are transcribed from the complementary
stand and provoke the degradation of the sense transcript via an RNAi-
mediated process and result in post-transcriptional regulation of gene expres-
sion (
Ji
n et al.,2008
). Similarly, evidence for epigenetic modifications (histone
acetylation and/or DNA methylation) were identified in several laccases gene
promoters and/or coding sequences (
Turlapati et al.,2011
). These modifica-
tions are known to affect gene expression and therefore represent another
potential mechanism by which laccases gene expression may be modified.
