Tissue-Specific Defense and Thermo-Adaptive Mechanisms of Soybean Seedlings under Heat Stress Revealed by Proteomic Approach

A comparative proteomic approach was employed to explore tissue-specific protein expression patterns in soybean seedlings under heat stress. The changes in the protein expression profiles of soybean seedling leaves, stems, and roots were analyzed after exposure to high temperatures. A total of 54, 35, and 61 differentially expressed proteins were identified from heat-treated leaves, stems, and roots, respectively. Differentially expressed heat shock proteins (HSPs) and proteins involved in antioxidant defense were mostly up-regulated, whereas proteins associated with photosynthesis, secondary metabolism, and amino acid and protein biosynthesis were down-regulated in response to heat stress. A group of proteins, specifically low molecular weight HSPs and HSP70, were up-regulated and expressed in a similar manner in all tissues. Proteomic analysis indicated that the responses of HSP70, CPN-60 beta, and ChsHSP were tissue specific, and this observation was validated by immunoblot analysis. The heat-responsive sHSPs were not induced by other stresses such as cold and hydrogen peroxide. Taken together, these results suggest that to cope with heat stress soybean seedlings operate tissue-specific defenses and adaptive mechanisms, whereas a common defense mechanism associated with the induction of several HSPs was employed in all three tissues. In addition, tissue-specific proteins may play a crucial role in defending each type of tissues against thermal stress.