In summary, we could show the involvement of a Hik8-cascade in the expression of genes involved in the glycolytic and OPP pathways induced by GPL, and another signal pathway under photosynthetic conditions in Synechocystis . The Hik8-cascade under GPL conditions may regulate glucose degradation to produce some energy and carbon compounds. This cascade might be important for the supply of organic materials such as amino acids and nucleotides through enhancement of the rates of the glycolysis and OPP pathways. Histidine kinase Hik8 upregulates the expression of one of the important glycolytic genes, fbaA, via sll1330 under heterotrophic growth conditions (i.e., in the presence of glucose with an indispensable short period of light) in Synechocystis sp. PCC 6803. In this study, expression of the genes for the glycolytic and OPP pathways was investigated using the wild type, and disruption mutants of Hik8 and sll1330, to determine whether or not the Hik8-involving signal transduction system generally regulates glucose catabolism. In the wild type, all the genes for the glycolytic and OPP pathways were upregulated under the same conditions as for fbaA. Analyses of the disruption mutants suggested that the signal transduction system involving Hik8 and Sll1330 plays a key role in the upregulation of genes such as pfkA, pgmB, and glk, and also that Hik8 induces genes including gap1 and pgk independently of Sll1330. This complicated signal transduction cascade, designated as the Hik8-cascade, occurs under heterotrophic growth with light pulses. In addition, a disruption mutant of a putative histidine kinase, sll1334, exhibited growth and gene expression patterns that suggested it to be a negative regulator in the cascade. Possible histidine kinases and response regulators as candidates for other components in the cascade are discussed.