Circadian phase-delay in the cmpR disrupted cyanobacterium Synechococcus sp. PCC 7942

Abstract

The pex gene extends the circadian period and pex mRNA is abundant in the darkness. This implied signal transduction pathway to the pex gene expression. Then, by using bioluminescence reporter strain for pex expression, we identified a pex expression mutant. The causative transposon insertion was occurred in cmpR gene coding a LysR-type DNA binding factor, CmpR. This regulates gene expression for bicarbonate transporter operon (Omata et al., 2001). Bioluminescence rhythm in the mutant showed circadian phase-delay by 6-hours as compared with the one in a wild-type reporter for the expression of clock operon kaiBC. This delay was complemented by transformation of the cmpR trans-gene. The phase-delay phenotype was partially suppressed by disruption of pex, suggesting that pex gene expression is required to the abnormal rhythm. From these results, it was revealed that cmpR and pex functioned to modulate phase of the circadian oscillator.