NtANTL2 overexpression regulates starch-related and nitrogen metabolism in tobacco plants

The function of the aromatic and neutral amino acid transporter gene ANT1-like (NtANTL2) was investigated. NtANTL2-3 over-expressor plants displayed greater tolerance to high nitrogen application compared to WT plants, characterized by better growth. As for carbon metabolism, the activity of sucrose phosphate synthetase in overexpression lines was 1.5 times higher than that in wild-type plants at 0.1% nitrogen, while sucrose synthase activity was significantly lower under all nitrogen levels. These changes in enzyme activities were closely associated with the differential gene expressions of GBSSI (granule-bound starcsssh synthase I), SUS (sucrose synthase), INV (invertase), and SPS (sucrose phosphate synthase). The activities and gene expressions of key enzymes in nitrogen metabolism like nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were also significantly affected. The GDH activity in overexpression lines was increased by 2.4-fold and 4.3 fold at 0.1% and 0.3% nitrogen, respectively. Increased levels of multiple amino acids besides aspartic acid content were found in NtANTL2 overexpression plants. These results clearly indicate the regulatory ability of NtANTL2 on amino acid composition and its central role in coordinating carbon and nitrogen metabolism balance.