Comparative Proteomics of Contrasting Maize Genotypes Provides Insights into Salt-Stress Tolerance Mechanisms

Salt
stress is a major abiotic factor limiting maize yield. To
characterize the mechanism underlying maize salt tolerance, we compared
the seedling root proteomes of salt-tolerant Jing724 and salt-sensitive
D9H. The germination rate and growth parameter values (weight and
length) were higher for Jing724 than for D9H under saline conditions.
Using an iTRAQ-based method, we identified 513 differentially regulated
proteins (DRPs), with 83 and 386 DRPs specific to Jing724 and D9H,
respectively. In salt-stressed Jing724, the DRPs were primarily associated
with the pentose phosphate pathway, glutathione metabolism, and nitrogen
metabolism. Key DRPs, such as glucose-6-phosphate 1-dehydrogenase,
NADPH-producing dehydrogenase, glutamate synthase, and glutamine synthetase,
were identified based on pathway enrichment and protein–protein
interaction analyses. Moreover, salt-responsive proteins in Jing724
seedlings were implicated in energy management, maintenance of redox
homeostasis, detoxification of ammonia, regulation of osmotic homeostasis,
stress defense and adaptation, biotic cross-tolerance, and regulation
of gene expression. Quantitative analyses of superoxide dismutase
activity, malondialdehyde content, relative electrolyte leakage, and
proline content were consistent with the predicted changes based on
DRP functions. Furthermore, changes in the abundance of eight representative
DRPs were correlated with the corresponding mRNA levels. Our results
may be useful for elucidating the molecular networks mediating salt
tolerance.