Proteomic profiling of an extreme halophyte Schrenkiella parvula with accelerated root elongation under mild salt stress.

Increased salinity in soil is one of the impacts of climate change and a major problem for crop cultivation. Halophytes have the ability to survive in hypersaline environments, and investigating their adaptation mechanisms is effective in imparting salt tolerance to plants. Recently, we discovered a strategy by the extreme halophyte Schrenkiella parvula to promote primary root elongation, a morpho-physiological response that may be given to have access to groundwater sources, while reducing meristem DNA replication, root hair development, and biomass at moderate salinities around 100 mM NaCl. However, when NaCl concentration exceeds 200 mM, seedling root elongation is inhibited, and seedlings change to respond to severe stress induced by salinity. To understand the interesting physiological and molecular mechanisms underlying primary root elongation at moderate salinity, we performed a proteomic analysis using two-dimensional gel electrophoresis and MALDI-TOF MS. Ultimately, a total of 300 different proteins were identified, of which 20 showed significant increases and 25 showed significant decreases at 100 mM NaCl. Among the increased proteins, proteins responding to abiotic stress such as glutathione transferases were found, and among the decreased proteins, proteins involved in glycolysis, purine nucleotide synthesis, and protein synthesis were found. Accumulation levels of proline, an osmotic regulator that inhibits root growth, were lower in S. parvula than in A. thaliana. On the other hand, interestingly, the expression levels of fructose-bisphosphate aldolase, sucrose phosphatase, and alpha-subunit of acetyl-CoA carboxylase increased. In addition, increases in P5CDH, an enzyme in the proline catabolism process, and decreases in GLN and GDH in glutamate synthesis in S. parvula suggest that these may lead to a fine-tuning of proline content. For annexins, a family of calcium -binding and membrane -bound proteins that regulate plant tolerance, moderate salt treatment showed a significant decrease in SpANN7, a non -significant downtrend for SpANN2, but no change for SpANN1. These findings suggest that the 100 mM NaCl does not create a serious stress for S. parvula. We also performed gene expression analysis of these altered proteins between S. parvula and A. thaliana. Taken together, in S. parvula roots, 100 mM NaCl partially induced the redox homeostasis system, stress response, and proline-mediated osmoregulation, moderately suppressing carbon metabolism, nucleotide, and protein synthesis to accelerate primary root elongation.