cDNA cloning and expression of the ADP-glucose pyrophosphorylase small subunit gene in sweet potato

ADP-glucose pyrophosphorylase (AGPase) is a key regulatory enzyme for the synthesis of starch in plants and of glycogen in bacteria, As the first step to understand the role of AGPase during development of the tuberous root in sweet potato, a partial cDNA encoding the small subunit of sweet potato AGPase (SAPS) was cloned and its transcriptional regulation was investigated, The deduced amino acid sequence of the cDNA was 94% identical to that of the small submit of potato AGPase and contained a conserved sequence motif that seemed to represent an allosteric activation in E, coli, Northern blot analysis showed that the level of the SAPS transcript was high in tuberous root and leaf, but not in nontuberous root, As the tuberous root enlarged from 0.3 cm to 3.5 cm in diameter, the expression level of SAPS was not significantly changed, In addition, the SAPS transcript level in the leaf increased with a concomitant increase of starch content when the leaf was exposed to light or when the cut end of the petiole was placed in either a sucrose or fructose solution in darkness, These results indicate that the SAPS gene is under metabolic control and is developmentally regulated.