The genome-wide transcriptional response to light in Pseudomonas putida KT2440

Pseudomonas putida KT2440 encodes 3 homologs of the LitR/CarH family (designated PplR1–PplR3; Pseudomonas putida light-induced transcription; regulator), which is an adenosyl B12-dependent light-sensitive MerR family transcriptional regulator. Transcriptome and individual transcriptional analysis revealed the existence of a number of photo-inducible genes including pplR1, phrB (encoding DNA photolyase), cfaA (cyclopropane synthase), folE (GTP cyclohydrolase I), cryB (cryptochrome-like protein), and multiple hypothetical genes. Transcriptional analysis based on a β-galactosidase reporter assay with single-, double-, and triple-knockout mutants of pplR1–pplR3 showed that deletion of pplR1–pplR3 completely abolished the light-inducible transcription in P. putida, which indicates that the transcription of light-inducible genes is under the ternary regulation of PplR proteins. DNase I footprint assay showed that PplR1 protein specifically binds to the promoter regions of light-inducible genes, suggesting a consensus PplR1-binding site, 5’-T(G/A)TACAn12TGTA(C/T)A-3’, predicted upon nucleotide sequence alignment. The disruption of cobalamin biosynthesis cluster did not affect the light-inducible transcription; however, disruption of ppSB1-LOV and ppSB2-LOV, a blue light photoreceptor genes, which are adjacent to pplR3 and pplR2, respectively, led to the complete loss of light-inducible transcription. Overall, the results suggest that 3 PplR and 2 PpSB-LOV regulate light-induced gene transcription in response to illumination. The high conservation of the pplR/ppSB-LOV cognate pair in Pseudomonas spp. suggests that the response and adaptation to light is similarly regulated in the group of non-phototrophic bacteria. Chromosomal RNA maps of wild-type cells cultured under the light conditions were compared with those of wild-type cells cultured under the dark conditions This is an Affymetrix custom-commercial tiling array that covers the Pseudomonas putida KT2440 chromosome (RefSeq: NC_002947) at 11-bp density. BPMAP files are provided as supplementary files. KT2440b520511FR-3.bpmap represents the forward strand of KT2440 chromosome, and KT2440b520511FF-3.bpmap represents the reverse strand of KT2440 chromosome.