Ethylene production has been achieved in cyanobacteria by introducing an exogenous ethylene forming enzyme(EFE)that using the TCA intermediate 2-oxoglutarate(2-OG)as one of its substrates.NtcA is a global nitrogen regulator.2-OG provides the carbon skeleton for the assimilation of nitrogen and can affect C/N balance by regulating the activity of NtcA.In addition,it was recently found that ntcA overexpression led to near 90%loss of intracellular 2-OG pool.As for the plasticity of the 2-OG metabolism in Synechocystis sp.PCC 6803,stable ntcA-deficient ethylene-producing recombinant strains were constructed to improve ethylene production.In the NtcA-deficient mutants,the growth rates decreased,and the phycocyanin changed along with growth stages.Our results indicated deficiency of ntcA could distribute more carbon flux toward EFE pathway,especially under high CO2 conditions.Moreover,the expression level of EFE,whose promoter is under control of NtcA,plays key role in the increased ethylene production.