Disclosed is an expression construct comprising SEQ ID NO. 7 for co-expression of the genes AspAT, GS and PEPCase comprising nucleotide sequences SEQ ID NO: 1, SEQ ID NO: 2 and SEQ ID NO: 3, linked to at least one control sequence and a transcription terminator sequence, useful for enhancing the carbon, nitrogen, biomass and yield of plants as compared to wild type or untransformed plant.