High-fluence blue light stimulates transcription from a higher plant chloroplast psbA promoter expressed in a cyanobacterium, Synechococcus (sp. strain PCC7942).

High-fluence white and blue light, but not red light, enhanced transcription of the barley chloroplast psbA promoter when heterologously expressed as a lacZ transcriptional fusion in the cyanobacterium, Synechococcus sp. strain PCC7942. Analysis of Arabidopsis thaliana phytochrome mutants, phyAphyB and hy2, indicated that a distinct blue phototransduction pathway stimulates psbA expression. The evolutionary implications of these findings are discussed.