3.5 Overexpression of MdASMT9 promoted TCA cycle and positively modulated amino acid metabolism
In the proteomic data, several upregulated DEPs (HK, FRK, GAD, GABA-T, and SSADH) were identified as involved in carbohydrate and N metabolism, potentially promoting TCA cycle (Figure 4c). To investigate this further, the contents of soluble sugars in WT and MdASMT9 -OE plants were measured. The results revealed that MdASMT9overexpression promoted the accumulation of sucrose, glucose and fructose under N-deficiency stress. As the TCA cycle accompanies amino acids synthesis and metabolism, the contents of nine amino acids in WT and MdASMT9 -OE lines were determined under normal N supply and N-deficiency conditions. After 35 d of N-deficiency treatment, the levels of most measured amino acids in all genotypes significantly decreased. However, compared to WT, the reduction in MdASMT9 -OE lines was less pronounced. The levels of six aromatic amino acids (ARG, GLU, HIS, LYS, THR, and ASP) were significantly higher inMdASMT9 -OE lines than in WT during N deficiency. These results indicate that the overexpression of MdASMT9 enhanced the TCA cycle and positively modulated amino acid metabolism to resist N-deficiency conditions.