Effect of expression of UDP-glucose pyrophosphorylase ribozyme and antisense RNAs on the enzyme activity and carbohydrate composition of field-grown transgenic potato plants

The effect of suppression of UDP-glucose pyrophosphorylase (UGPase, UTP alpha-D-glucose-1-phosphate uridylyl transferase, EC2.7.7.9) on carbohydrate metabolism in potato tubers was investigated. Constructions expressing a UGPase-specific ribozyme or a UGPase antisense RNA based on the genomic sequence, each under the control of the 35S promoter of the Cauliflower Mosaic Virus, were tested. Out of 103 plants transformed with the constructs, only 13 showed levels of UGPase activity significantly different from the control. No transgenic plants, carrying either construct, expressed an enzyme activity lower than 50-60% of the control. Plants of seven clones were grown in the field, and UGPase activity, and the level of sugars were measured in the tubers. After storage at room temperature for one week, tubers of six of these had sucrose levels significantly (P < 0.05) lower than in control tubers. In tubers of four clones, the difference was maintained after two months storage at 10 degrees C, and in two clones it persisted two months after storage at 6 degrees C. The results indicate that UGPase limits the rate of UDP-glucose synthesis in stored tubers and potentially can be used to control the reduced-sugar accumulation during cold-storage.