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Molecular
characterization of a novel stress-inducible antioxidant gene, XvPer1,
from the resurrection plant Xerophyta
viscosa Baker.
S.B. Mowla,
J.A. Thomson, J.M. Farrant, S. G. Mundree
Environmental stresses occur in various parts of the
world, especially in response to global climate change. As a result,
crop plant productivity is negatively affected globally, but more so in
sub-Saharan Africa. The presence of high light intensities often occurs
in addition to water limitation and can be extremely damaging to
photosynthetically active tissues leading to the formation of oxygen
free radicals. If unquenched, these molecules cause considerable damage
to the subcellular milieu. Reactive oxygen species (ROS) play a
significant role in causing damage to living cells under severe stress
conditions. To combat oxidative stress, complex protective mechanisms
have been evolved by plants to mitigate and repair the damage initiated
by free-radicals. By differential screening of a X. viscosa cDNA library, genes were identified that were upregulated
when the plant was in a dehydrated state. XvPer1 was one of them, coding
for a novel antioxidant enzyme. A
cDNA named XvPer1
was isolated from X.
viscosa by differential screening of a cDNA library.
Characterization of the cDNA showed that XvPer1 has an ORF of 849 bp encoding a polypeptide of 210 residues.
The XvPer1 cDNA contains a
putative polyadenylation site and codes for a putative bipartite nuclear
localization signal (NLS) near the 3’-end. The cDNA corresponds to
1-Cys peroxiredoxin, an evolutionary conserved thiol-specific
antioxidant enzyme. XvPer1 polypeptide shows significant sequence
identity (~70%) to other recently identified plant 1-Cys peroxiredoxins.
The amino acid sequence proposed to constitute the active site of the
enzyme (PVCTTE) is highly conserved in XvPer1. Southern blot analysis
revealed a single copy of XvPer1
in the genome. Analysis of the gene expression using northern blot
indicated that the transcript is absent in fully hydrated X. viscosa tissues but is induced under abiotic stresses such as
dehydration, heat (42oC), high light (1500 mmol
m-2 s-1) and when treated with abscisic acid (100 mM)
and sodium chloride (150 mM). Western blot data correlated with the
patterns of expression of XvPer1.
Preliminary localization studies using immunofluorescence revealed that
XvPer1 is localized in the nucleus of dehydrated X.
viscosa leaf cells. These results suggest that the stress-inducible
gene Xvper1 may function to
protect nucleic acids within the nucleus against oxidative injury.
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