Genetic Engineering of “C4 Rice”: Expression of Maize PEP Carboxykinase in Rice Mesophyll Chloroplast to Raise CO2 Concentration and Photosynthesis

PhosphoEnolPyruvate Carboxykinase (Pck) Is A C4-Acid Decarboxylation Enzyme Located In The Cytosol Of Bundle Sheath Cells Of Pck Subtype C4 Plants. In This Study, We Have Introduced The Maize Pck Gene Into Rice Genome And Targeted The Enzyme To Mesophyll Chloroplast As A First Step In An Attempt To Raise Co2 Concentration In The Chloroplast Of Rice Via Decarboxylation Of Oxaloacetate. Molecular Analyses Confirmed The Integration Of The Maize Gene Into Rice Genome And Its Expression At Transcript Level In Several Transgenic Lines. Although Expression Of The Maize Pck Gene In Transgenic Rice Plants Was Driven By The Tomato RbcS3C Promoter The Protein Was Expressed In An Organ-Specific Manner: High In Leaf, Stem And Floret, But Not In Root. The Protein Amounts In The Leaf Were 4–6 Fold Higher In Transgenic Than In Wild Type Plants. The Photosynthetic Rates Of Three Greenhouse Grown Transgenic Lines Were Comparable Or Slightly Higher Than That Of Untransformed Wild Type Plants. In A Preliminary Field Trial, Transgenic Rice Plants Exhibited Enhanced Growth (20–50%) And Grain Yields (10–50%) Than Did Wild Type. Since Pck Is Only One Of The Biochemical Steps In The Entire C4 Pathway Other Affiliated Mechanisms, Such As Effective Co2 Acquisition And Rapid Carboxylation By Pep Carboxylase, Will Have To Be In Place In Order To Have A Functional “C4 Rice”.