A light regulated OmpR-class promoter element co-ordinates light-harvesting protein and chromophore biosynthetic enzyme gene expression.
Co-ordination of chromophore and apoprotein biosynthesis is required during photosynthetic light-harvesting antennae production, such as occurs during complementary chromatic adaptation (CCA). This response to ambient light colour changes is controlled by a phytochrome-class photoreceptor and involves changes in the synthesis of cyanobacterial light-harvesting antennae. During growth in red light, CCA activates cpc2 transcription, an operon that encodes the light-harvesting protein phycocyanin. In order to function, this apoprotein must have covalently attached phycocyanobilin chromophores, which are synthesized by PcyA. We show that pcyA is also transcriptionally activated by CCA during red light growth and is not regulated via feedback that senses cpc2 RNA levels. The pcyA and cpc2 promoters contain a common regulatory element, a direct repeat typical of OmpR-class transcription factor binding sites, at similar positions relative to their red light-controlled transcription start sites. Deletion of this element from the pcyA promoter eliminated CCA-regulated transcription, and insertion of the element into a non-light responsive promoter conferred CCA regulation. We conclude that this element is necessary and sufficient to confer CCA transcriptional regulation and that it co-ordinates phycocyanin and phycocyanobilin biosynthesis in red light.
Alvey
Richard M
RM
Department of Biology, 1001 East Third Street, Indiana University, Bloomington, IN47405, USA.
Bezy
Ryan P
RP
Frankenberg-Dinkel
Nicole
N
Kehoe
David M
DM
D000222:Adaptation, Physiological / Q000528:radiation effects; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D016000:Cluster Analysis; D000458:Cyanobacteria / Q000235:genetics* / Q000528:radiation effects; D025461:Feedback, Physiological / Q000528:radiation effects; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects*; D005798:Genes, Bacterial; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000235:genetics* / Q000528:radiation effects; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000378:metabolism; D052980:Phycobilins / Q000096:biosynthesis*; D045524:Phycobilisomes / Q000378:metabolism / Q000528:radiation effects; D010798:Phycocyanin / Q000096:biosynthesis*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics*; D024363:Transcription Initiation Site; D014158:Transcription, Genetic / Q000528:radiation effects
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D052980:Phycobilins; D045524:Phycobilisomes; D012329:RNA, Bacterial; D015534:Trans-Activators; C112177:osmolarity response regulator proteins; D010798:Phycocyanin; C011069:phycocyanobilin; D010088:Oxidoreductases