ADP-glucose pyrophosphorylase genes are differentially regulated in sugar-dependent or -independent manners in tomato ( L.) fruit.

In early developing tomato ( L.) fruit, starch accumulates at high levels and is used by various primary metabolites in ripening fruits. ADP-glucose pyrophosphorylase is responsible for the first key step of starch biosynthesis. Although it has been reported that and isoforms are mainly expressed in early developing fruit, their regulatory mechanism has not been elucidated. The present study investigated the transcriptional response of and to various metabolizable sugars, nonmetabolizable sugar analogues, hexokinase inhibitors and proline by an experimental system using half-cut fruits. was upregulated in response to sucrose and constituted hexoses such glucose, whereas the gene almost did not exhibit a prominent sugar response. Further analyses revealed that other disaccharides such maltose and trehalose did not show a remarkable effect on both and expressions. These results indicate that there are two distinct regulatory mechanisms, namely, sugar metabolism-dependent and -independent, for the regulation of AGPase gene expression. Interestingly, the ADP treatment, a hexokinase inhibitors, cancelled the sugar response of , indicating that hexokinase-mediated sugar signaling should be involved in the sugar response of These results suggest that sugar-dependent () and sugar-independent () pathways coordinatively regulate starch biosynthesis in immature tomato fruit.