Amino acid metabolism response to post-anthesis drought stress during critical periods of elite wheat (Triticum aestivum L.) endosperm development

Drought is an important environmental factor leading to wheat yield loss in arid areas. The accumulation of amino acids during the filling stage is closely related to wheat drought resistance and yield, but the mechanism is still unclear. In this study, winter wheat plants (cultivars Xindong 18 (XD18) and Xindong 22 (XD22)) were subjected to post-anthesis drought treatment (DT) and sufficient water treatment (WT), and the measurement of free amino acid and carbohydrates content and the proteomic and transcriptomic analysis of wheat grains were conducted 7 and 14 days after anthesis (DAA). Finally, the improvement effect of application of exogenous glutamate (Glu) on the drought resistance of wheat was validated by hydroponic and field experiments. The results showed that sucrose and soluble sugar contents of XD22 grains were higher than those of XD18 grains under DT. The grain weight and filling rate of both wheat cultivars increased in the early stage of DT but reduced in the late stage. The content of most free amino acids in grains reduced under DT, but the Glu content increased. Regression analysis of grain weight and free amino acid content found that Glu was involved in the responses of wheat to DT and WT. The transcriptomic analysis results showed that XD18-DT7/WT7 and XD22-DT7/WT7 had 161 and 350 differentially expressed genes (DEGs) related to amino acid metabolism, respectively, and XD18DT14/WT14 and XD22-DT14/WT14 had 380 and 326 DEGs related to amino acid metabolism, respectively. Proteomic analysis results showed that XD18-DT7/WT7 and XD22-DT7/WT7 had 163 and 117 differentially expressed proteins (DEPs) related to amino acid metabolism, respectively, and XD18-DT14/WT14 and XD22DT14/WT14 had 29 and 109 DEPs related to amino acid metabolism, respectively. Besides, the expression level of most DEPs involved in Glu metabolism (> 95 %) was significantly up-regulated at the early stage of DT. It should be noted that the application of different concentrations of exogenous Glu at seedling stage, heading stage, and flowering stage significantly reduced wheat root/shoot ratio and relative conductivity (RC) under DT, and increased the SPAD value, grain weight, and filling rate. The free amino acids and carbohydrates in wheat grains changed significantly under DT, and a large number of DEPs involved in the Glu metabolism pathway were up-regulated to cope with drought stress. Finally, exogenous Glu application can improve the drought resistance of drought-stressed wheat at seedling and filling stages and increase grain weight.