Environmental control of phosphorylation pathways in a branched two-component system.
NblS, the most conserved histidine kinase in cyanobacteria, regulates photosynthesis and acclimatization to a variety of environmental conditions. We used in silico, in vivo and in vitro approaches to identify RpaB and SrrA as the cognate response regulators of NblS and to characterize relevant interactions between components of this signalling system. While genetic analysis showed the importance of the NblS to RpaB phosphorylation branch for culture viability in Synechococcus elongatus PCC 7942, in vitro assays indicated a strong preference for NblS to phosphorylate SrrA. This apparent discrepancy can be explained by environmental insulation of the RpaB pathway, achieved by RpaB-dependent repression of srrA under standard, low light culture conditions. After a strong but transient increase in srrA expression upon high light exposure, negative regulation of srrA and other high light inducible genes takes place, suggesting cooperation between pathways under environmental conditions in which both RpaB and SrrA are present. Complex regulatory interactions between RpaB and SrrA, two response regulators with a common evolutionary origin that are controlled by a single histidine kinase, are thus emerging. Our results provide a paradigm for regulatory interactions between response regulators in a branched two-component system.
Instituto de Biomedicina de Valencia (CSIC), 46010 Valencia, Spain.
Maria Luisa
ML
López-Redondo
Felix
F
Moronta
Paloma
P
Salinas
Javier
J
Espinosa
Raquel
R
Cantos
Ray
R
Dixon
Alberto
A
Marina
Asunción
A
Contreras
D000064:Acclimatization; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D000071677:Histidine Kinase; D008027:Light; D050296:Microbial Viability; D010766:Phosphorylation; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D018085:Regulon; D015398:Signal Transduction; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects
D001426:Bacterial Proteins; D011494:Protein Kinases; D000071677:Histidine Kinase