Agriculture Reference
In-Depth Information
or stems, and abiotic stimuli such as seawater, NaCl, ABA, and PEG triggered
a significant induction of SpFBA in the roots within 2-12 h [78]. Over-
expression of recombinant SpFBA resulted in an increased tolerance to salinity
in transgenic
E. coli
. The protein osmotin was found to accumulate during
adaptation of tobacco cells to high osmotic stress, including salt or
polyethylene glycol treatment [79, 80]. These results suggest that FBP aldolase
and osmotin play roles in salt-tolerance mechanisms common to both
glycophytes and mangrove plants. The abundance of these proteins did not
correlate with the expression levels of their respective mRNAs, as revealed by
microarray analysis. A novel salt-responsive protein was also identified by this
proteomic
analysis,
and
may
provide
insight
into
the
salt-tolerance
mechanisms of mangroves.
3.
G
ENE
R
EPRESSION
P
LAYS A
R
OLE IN
P
LANT
S
ALT
T
OLERANCE
There have been several reports of the involvement of repression or
silencing of genes in salt tolerance of glycophytes. Small 21-25-nt noncoding
RNAs, such as microRNAs (miRNA) and short interfering RNAs (siRNA),
have recently emerged as important regulators of both transcriptional and
posttranscriptional gene silencing [81]. miRNAs are generated from longer
hairpin-structured precursor RNAs that are transcribed from endogenous
noncoding genes by endonucleolytic processing of the ribonuclease III-like
enzyme, Dicer [82]. siRNAs were first identified in plants undergoing
posttranscriptional gene silencing [83]. siRNAs differ from miRNAs in that
they are generated from long double-stranded RNAs (dsRNAs) by antisense
transcription or the activity of cellular RNA-dependent RNA polymerases
(RdRPs) [84].
Recently, several miRNAs and siRNAs have been reported to be involved
in abiotic stress responses in
Arabidopsis
[85, 86]. Drought, high salinity, cold
and ABA treatments strongly up-regulated miR393, which targets the F-box
protein, TIR1 [85]. TIR1 is an auxin receptor, and down-regulation of TIR1 by
miR393 could reduce auxin signaling and seedling growth under stress
conditions. Stress-induced or up-regulated miRNAs are expected to target
negative regulators of stress responses or positive regulators of processes that
are inhibited by stress. The miRNAs miR397b and miR402, which target
laccases and a putative DNA glycosylase, respectively, were also slightly up-
