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Komatsu et al. [ 28 ] exploited proteomic technique in combination
with transcriptomic to unravel the underlying molecular mecha-
nism of soybean conferring fl ooding tolerance. High-coverage
gene expression profi ling analysis was carried out after 12 h of
fl ooding of 2 days old soybean seedlings. Transcriptome technique
revealed that genes associated with alcohol fermentation, ethylene
biosynthesis, pathogen defense, and cell wall loosening were sig-
nifi cantly upregulated following fl ood-induced stress. In total, 97
genes and 34 proteins were found to be altered after fl ooding.
Interestingly, disease/defense-related proteins were increased at a
transcriptional level but were decreased at a translational level fol-
lowing fl ooding. Altered expressions of hemoglobin, acid phos-
phatase, and Kunitz trypsin protease inhibitor were evident at both
transcriptional and translational levels. However, abundance of
molecular chaperons and ROS scavengers were changed only at
the translational level. Findings of this study indicate that early
responses might be important stress adaptation factors to ensure
survival of the soybean plants against fl ood-induced hypoxia.
Separate study revealed that proteins related to glycolysis and ROS
scavenging were increased in roots of 2 days old soybeans exposed
to 1 day of fl ooding stress [ 29 ].
In contrast to other increased ROS scavenging enzymes, two
ascorbate peroxidases (APXs) were found to be decreased in
response to fl ooding. This fi nding is consistent with the previous
proteomic study by Shi et al. [ 30 ]. Authors identifi ed ten
fl ood-responsive proteins, among which cytosolic APX 2 was pre-
dominantly decreased under flooding condition. Northern-
hybridization also confi rmed that the abundance of cytosolic APX
2 transcript decreased signifi cantly after fl ooding, as did the enzy-
matic activity of APX. Results suggest that cytosolic APX 2 is
involved in fl ood-induced stress response of young soybean seed-
lings. A recent analysis of proteomic changes in roots of 2 days old
soybean seedlings at post-fl ooding recovery stage identifi es seven
proteins involved in cell wall modifi cation and S -adenosylmethionine
synthesis [ 16 ]. Comparative root proteome analysis of control and
3-day fl ooding-experienced soybean reveals 70 differentially
expressed protein spots, primarily involved in protein destination/
storage and metabolic processes. Clustering analysis of the differ-
entially expressed protein spots strongly indicates that 3 days of
fl ooding causes signifi cant changes in protein expression, even dur-
ing post-fl ooding recovery period. Three days of fl ooding results
in decrease of ion transport-related proteins and increase of pro-
teins involved in cytoskeletal reorganization, cell expansion, and
programmed cell death. Results indicate that alteration of cell
structure through changes in cell wall metabolism and cytoskeletal
organization may be involved in post-fl ooding recovery processes
in soybean seedlings.
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