Comparative analysis of metabolic proteome variation in ascorbate-primed and unprimed wheat seeds during germination under salt stress.

Seed priming with ascorbic acid improves salt tolerance in durum wheat. For understanding the potential mechanisms underlying this priming effect a gel-free shotgun proteomic analysis was performed comparing unprimed to ascorbate-primed wheat seed during germination under saline and non-saline conditions. Since seed germination is the result of interplay or cross-talk between embryo and embryo-surrounding tissues, we studied the variation of metabolic proteome in both tissues separately. 167 of 697 identified and 69 of 471 identified proteins increase or decrease in abundance significantly in response to priming and/or salinity compared to untreated, unstressed control in embryo and embryo-surrounding tissues, respectively. In untreated wheat embryo salt stress was accompanied by change in 129 proteins, most of which are belonging to metabolism, energy, disease/defense, protein destination and storage categories. Ascorbate pretreatment prevents and counteracts the effects of salinity upon most of these proteins and changes specifically the abundance of 35 others proteins, most of which are involved in metabolism, protein destination and storage categories. Hierarchical clustering analysis revealed three and two major clusters of protein expression in embryo and embryo-surrounding tissues, respectively. This study opens promising new avenues to understand priming-induced salt tolerance in plants. BIOLOGICAL SIGNIFICANCE: To clearly understand how ascorbate-priming enhance the salt tolerance of durum wheat during germination, we performed for the first time a comparative shotgun proteomic analysis between unprimed and ascorbate-primed wheat seeds during germination under saline and non-saline conditions. Furthermore, since seed germination is the result of interplay or cross-talk between embryo and embryo-surrounding tissues we analyzed the variation of metabolic proteome in both tissues separately. 1168 proteins exhibiting greater molecular weight diversity (ranging from 5 to 258kDa) were identified. Among them, 167 and 69 proteins were increased or decreased in abundance significantly by priming and/or salinity as compared to control, in embryo and embryo-surrounding tissues respectively. Ascorbate pretreatment alleviates the effects of salinity upon most of these proteins, particularly those involved in metabolism, energy, disease/defense, protein destination and storage functions. Hierarchical clustering analysis revealed three and two major clusters of protein accumulation in embryo and embryo-surrounding tissues, respectively. These results may provide new avenues for understanding and advancing priming-induced salt tolerance in crop plants.