Agriculture Reference
In-Depth Information
sequenced and annotated hundreds of times. For example, metallothionein 2a
was identified 487 times in
H. littoralis
and a Pfkb-type carbohydrate kinase
family protein in
R. mangle
was annotated 861 times. Within the top 20 most
frequently-returned annotations, there were a number of genes unique to each
species. A particularly interesting example was
Bg70
, which appeared 756
times in
R. mangle
, but was absent from
H. littoralis
. This gene family of
unknown function was previously reported to be specific to
B. gymnorhiza
[29] and has been reported to be highly expressed in salt-treated plants [73].
Overexpression of a
Bg70
clone conferred enhanced salt tolerance to
Agrobacterium
and
Arabidopsis
[62]. These results suggest that these
mangrove-specific genes contribute to salt tolerance. Other examples of
frequently-sequenced transcripts include chloroplast DNA and MIOX1 (myo-
inositol oxygenase) in
H. littoralis
and β-lactamase, LTP4 (lipid transfer
protein 4), phosphorylase family protein, and PBB2 (20S proteosome β
subunit B2) in
R. mangle
[55]. DNA encoding ATUBC2 (ubiquitin-
conjugating enzyme 2) and mitochondrial transcription termination factor
family protein were frequently sequenced in both species. The development
and application of novel investigatory techniques will continue to provide
insights into the molecular mechanisms of plant salt tolerance.
2.4.3. Proteome Analysis of Mangroves
Proteomic techniques have also been applied to the identification of key
proteins in the regulation of salt tolerance in
B. gymnorhiza
[76, 77]. Two-
dimensional electrophoresis followed by N-terminal amino acids sequencing
of leaf extract revealed the expression of the oxygen evolving enhancer protein
1 (OEE1) precursor [76]. OEEs are chloroplast proteins that are peripherally-
bound to photosystem II on the laminal side of the thylakoid membrane.
Prompt turnover of OEEs might be a compensatory mechanism to cope with
the effects of damaged OEEs. Similarly, comparative two-dimensional
electrophoresis revealed differential expression of proteins in the main root,
lateral root and leaf of
B. gymnorhiza
in response to salt stress [77]. Among
these, three proteins were identified by internal peptide sequence analysis:
fructose-1,6-bisphosphate aldolase (FBP aldolase) and a novel protein in the
main root, and osmotin in the lateral root. Enhanced expression of FBP
aldolase would results in increased flow of carbon through the Calvin cycle,
which leads to an increase in sucrose and amino acid production through
glycolysis. These effects would also lead to increased osmolite production and
contribute to stress tolerance. FBP aldolase in the halophyte
Sesuvium
portulacastrum
(SpFBA) was more strongly expressed in roots than in leaves
