Effect of over-expression of an E. coli fructose 1,6-bisphosphate aldolase gene in planta on photosynthesis, carbon metabolism and plant growth

Abstract

Fructose 1,6 biphosphate aldolase (fda) is an enzyme catalyzing a reversible reaction converting triose phosphate to fructose 1,6 bisphosphate. This reaction occurs in both chloroplast (the Calvin cycle and starch synthesis) and cytosol (sucrose synthesis and glycolysis). To study whether fda plays any important roles in controlling photosynthesis, metabolic flux and plant growth we have successfully increased its activity in planta by transforming an E. coli class II fda gene into tobacco, potato and cotton under the control of a constitutive promoter. This E. coli fda enzyme differs from its plant counterpart which is a class I enzyme in that the E. coli enzyme is a metalloaldolase and the plant enzyme is a Schiff base-forming aldolase. When expressed in planta, the E. coli fda protein is specifically targeted into chloroplast through a chloroplast targeting sequence. Transgenic cotton plants expressing the E. coli fda showed up to 6-fold increase in fda activity, little effect on photosynthesis, but altered carbon partitioning and significant increase in starch accumulation in leaves. Under the standard greenhouse conditions trangenic cotton plants showed improved boll retention and lint yield. Significant increase in root biomass and tuber yield were observed in the transgenic tobacco and potato, respectively.