Table 2.

Effect of transgene expression on metabolite levels in transgenic plants.

Genetic Construct	Conditions	Technique	Core Metabolomic Results (Compared to WT)	References
N metabolism
Oryza sativa GS1;1 and GS1;2 overexpressed in Oryza sativa cv. Zhonghua 11 under the control of the CaMV 35S promoter	Metabolic analysis done on tillering stage roots and shoots of plants growth with Low N and Moderate N	GC-TOF-MS	Low N: GS1;1 and GS1; 2 increased sugars, organic acids, free amino acids in shoots and decreased in roots. Moderate N: same results for both lines in shoots as for low N, in roots GS1;1 increased sugars, organic acids and free amino acids GS1;2 roots had decreased metabolites.	[41]
Pisum sativum AS1 overexpressed in Nicotiana tabacum under the control of the CaMV 35S promoter	16 h light/8 h dark, 21 day old plants grown in sand, fertilized with Hoagland solution with 10 mM NO3−	HPLC	10–100 fold increased Asn. Decreased Gln, Asp. No change in Glu.	[46]
Hordeum vulgare AlaAT overexpressed in Oryza sativa under the control of the root-specific OsANT1 promoter	14 h light/10 h dark, 45 day old plants grown hydroponically in 0.5, 2.0, and 5.0 mM NH4+	HPLC	Increased Gln, Glu, Asn, Asp, and Arg in roots and shoots.	[12]
N recycling/protein degradation/C:N balance
Mus musculus ODC overexpressed in Populus nigra under the control of a 2X CaMV 35S promoter	Cell cultures grown in MS media	HPLC	Increased Ala, Thr, Val, Ile, and GABA. Decreased Gln, Glu, Orn, Arg, His, Ser, Gly, Cys, Phe, Trp, Asp, Lys, Leu, Met.	[53]
Arabidopsis FUM2 overexpressed in Arabidopsis under the control of a 2X CaMV 35S promoter	8 h light/16 h dark, plants grown for 42 days with 1.25 mg (low) or 31.5 mg (high) inorganic nitrogen	GC-MS	Increased starch, FUM2 knockouts reduced fumarate levels, varied amino acid levels according to light cycle.	[54]
Regulatory transgenes
Zea mays Dof1 expressed in Arabidopsis under the control of the CaMV 35S promoter; also expressed in potato	Constant light, plants grown on modified MS medium; low N = 1 mM NH4NO3/1 mM KNO3; high N = 10 mM NH4NO3/10 mM KNO3	Hitachi amino acid analyzer; enzymatic assay	Increased total [amino acid], NH4+ Decreased glucose, malate No change in sucrose, citrate, or 2-OG Similar to transgenic potato	[48]
Zea mays Dof1 expressed in Oryza sativa under the control of the CaMV 35S promoter	14 h day/10 h night, hydroponic growth at 360 (high) or 90 µM (low) NH4+	CE-MS/MS	Increased concentration of some amino acids under high and low [N]	[49]
N-responsive transgenes
Oryza sativa ENOD93 expressed in Oryza sativa under the control of the 35S C4PDK promoter	16 h day/8 h night for 4 weeks then 10 h day/14 h night for 1 week for flowering, soil growth at 1 mM (low), 5 mM (median) or 10 mM (high) nitrate	Biochemical assays	Increased total amino acids in OsENOD93-ox line roots in all N levels but more so under N stress. No increase in amino acid levels in shoots. Higher biomass in OsENOD93-ox.	[52]
Co-expressed N metabolism and Regulatory transgenes
Arabidopsis Dof1, GS1, GS2 expressed in tobacco under the control of the leaf specific rbcS promoter from tomato	Growth in perlite and low N nutrient solution for 60 and 90 days	RP-HPLC and biochemical assays	Transgenic tobacco co-expressing Dof1, GS1, GS2 had increased amino acids, glucose, sucrose and decreased nitrate, malic acid, citric acid and showed growth advantages	[43]