The promoter of CBL-interacting protein kinase 15 delivers the interference of sugar regulation by perturbed oxidative phosphorylation

To carefully assess the sugar regulation of the CBL-interacting protein kinase 15 (CIPK15) promoter, we established two transgenic rice cell lines that contained the β-glucuronidase gene under the control of the CIPK15 promoter. In these cells, CIPK15 promoter activity was effectively suppressed by glucose compared to the promoter activity in starved cells. However, such sugar suppression was abolished upon O₂ deprivation and by inhibition of oxidative phosphorylation. Therefore, crosstalk between sugar regulation and metabolic status occurs at the CIPK15 promoter. A transient expression assay demonstrated that sugar regulation of the firefly luciferase gene under the control of the Amy3D promoter was also affected in the same way, by either anoxic conditions or inhibition of oxidative phosphorylation. Since the expression pattern of both the CIPK15 and Amy3D promoters is the same with respect to sugar regulation and susceptibility to anaerobic conditions, the two promoters may share cis-element(s). Alternatively, anoxic interference of Amy3D gene regulation may simply be due to regulation of the CIPK15 gene, a key upstream regulator of the signaling cascade for Amy3D expression. Therefore, using computer-assisted sequence analyses, we carefully searched the CIPK15 and Amy3D promoters for conserved sequences and potential cis-element(s) that might be involved in such a crosstalk.