Limits...
Interaction of two photoreceptors in the regulation of bacterial photosynthesis genes.

Metz S, Haberzettl K, Frühwirth S, Teich K, Hasewinkel C, Klug G - Nucleic Acids Res. (2012)

Bottom Line: Here we show that CryB interacts with the C-terminal domain of AppA and modulates the binding of AppA to the transcriptional repressor PpsR in a light-dependent manner.Consequently, binding of the transcription factor PpsR to its DNA target is affected by CryB.These results elucidate for the first time how a bacterial cryptochrome affects gene expression.

View Article: PubMed Central - PubMed

Affiliation: Institut für Mikrobiologie und Molekularbiologie, Universität Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.

ABSTRACT
The expression of photosynthesis genes in the facultatively photosynthetic bacterium Rhodobacter sphaeroides is controlled by the oxygen tension and by light quantity. Two photoreceptor proteins, AppA and CryB, have been identified in the past, which are involved in this regulation. AppA senses light by its N-terminal BLUF domain, its C-terminal part binds heme and is redox-responsive. Through its interaction to the transcriptional repressor PpsR the AppA photoreceptor controls expression of photosynthesis genes. The cryptochrome-like protein CryB was shown to affect regulation of photosynthesis genes, but the underlying signal chain remained unknown. Here we show that CryB interacts with the C-terminal domain of AppA and modulates the binding of AppA to the transcriptional repressor PpsR in a light-dependent manner. Consequently, binding of the transcription factor PpsR to its DNA target is affected by CryB. In agreement with this, all genes of the PpsR regulon showed altered expression levels in a CryB deletion strain after blue-light illumination. These results elucidate for the first time how a bacterial cryptochrome affects gene expression.

Show MeSH

Related in: MedlinePlus

Expression changes of selected genes as determined by real-time RT–PCR. Bars indicate gene expression in the cryB deletion mutant compared to the wild-type after 60 min blue light treatment under semiaerobic growth conditions. White bars correspond to genes of the PpsR operon, bars in black depict control genes of the PrrA operon (31,32) Numbers correspond to R. sphaeroides gene annotations. RSP_2879, putative uncharacterized protein. The mean of three experiments is given and standard deviation is indicated.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3401432&req=5

gks243-F6: Expression changes of selected genes as determined by real-time RT–PCR. Bars indicate gene expression in the cryB deletion mutant compared to the wild-type after 60 min blue light treatment under semiaerobic growth conditions. White bars correspond to genes of the PpsR operon, bars in black depict control genes of the PrrA operon (31,32) Numbers correspond to R. sphaeroides gene annotations. RSP_2879, putative uncharacterized protein. The mean of three experiments is given and standard deviation is indicated.

Mentions: Our earlier observation that CryB affects the expression of puf and puc genes (15) is in agreement with our finding that CryB modulates binding of PpsR to target sequences, since puf and puc genes are part of the PpsR regulon. Consequently, CryB should also affect the expression of all other members of the PpsR regulon (31,32). In order to verify this, the expression levels of these genes were compared in the wild-type 2.4.1 and in the mutant 2.4.1ΔcryB (15). The differences in expression levels between the two strains when grown under microaerobic conditions were too low to reveal reproducible and significant results. We therefore quantified gene expression in cultures illuminated with blue light for 60 min by real-time RT–PCR. As shown in Figure 6 all genes belonging to the PpsR regulon were affected by the lack of CryB. The expression levels in the mutant strain were 1.4–2.6-fold lower than in the isogenic wild-type strain. Most of these genes encode genes required for the synthesis of pigment binding proteins (puf, puc), synthesis of bacteriochlorophyll (bch) or carotenoids (crt) and are clustered on the chromosome. Genes hemC and hemE required for heme synthesis and argD (acetyl ornithine aminotransferase) are localized in distinct regions on the chromosome but show similar CryB dependence. We included two genes in our study, which are part of the PrrA regulon (32) but not of the PpsR regulon, ccpA and RSP2877. PrrA is another important regulator of photosynthesis genes, including the puf and puc operons and induces transcription at low oxygen tension. The expression levels of these two genes did not differ significantly in the two strains excluding the possibility that CryB affects photosynthesis gene expression solely through PrrA or has a general, unspecific effect on gene expression.Figure 6.


Interaction of two photoreceptors in the regulation of bacterial photosynthesis genes.

Metz S, Haberzettl K, Frühwirth S, Teich K, Hasewinkel C, Klug G - Nucleic Acids Res. (2012)

Expression changes of selected genes as determined by real-time RT–PCR. Bars indicate gene expression in the cryB deletion mutant compared to the wild-type after 60 min blue light treatment under semiaerobic growth conditions. White bars correspond to genes of the PpsR operon, bars in black depict control genes of the PrrA operon (31,32) Numbers correspond to R. sphaeroides gene annotations. RSP_2879, putative uncharacterized protein. The mean of three experiments is given and standard deviation is indicated.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3401432&req=5

gks243-F6: Expression changes of selected genes as determined by real-time RT–PCR. Bars indicate gene expression in the cryB deletion mutant compared to the wild-type after 60 min blue light treatment under semiaerobic growth conditions. White bars correspond to genes of the PpsR operon, bars in black depict control genes of the PrrA operon (31,32) Numbers correspond to R. sphaeroides gene annotations. RSP_2879, putative uncharacterized protein. The mean of three experiments is given and standard deviation is indicated.
Mentions: Our earlier observation that CryB affects the expression of puf and puc genes (15) is in agreement with our finding that CryB modulates binding of PpsR to target sequences, since puf and puc genes are part of the PpsR regulon. Consequently, CryB should also affect the expression of all other members of the PpsR regulon (31,32). In order to verify this, the expression levels of these genes were compared in the wild-type 2.4.1 and in the mutant 2.4.1ΔcryB (15). The differences in expression levels between the two strains when grown under microaerobic conditions were too low to reveal reproducible and significant results. We therefore quantified gene expression in cultures illuminated with blue light for 60 min by real-time RT–PCR. As shown in Figure 6 all genes belonging to the PpsR regulon were affected by the lack of CryB. The expression levels in the mutant strain were 1.4–2.6-fold lower than in the isogenic wild-type strain. Most of these genes encode genes required for the synthesis of pigment binding proteins (puf, puc), synthesis of bacteriochlorophyll (bch) or carotenoids (crt) and are clustered on the chromosome. Genes hemC and hemE required for heme synthesis and argD (acetyl ornithine aminotransferase) are localized in distinct regions on the chromosome but show similar CryB dependence. We included two genes in our study, which are part of the PrrA regulon (32) but not of the PpsR regulon, ccpA and RSP2877. PrrA is another important regulator of photosynthesis genes, including the puf and puc operons and induces transcription at low oxygen tension. The expression levels of these two genes did not differ significantly in the two strains excluding the possibility that CryB affects photosynthesis gene expression solely through PrrA or has a general, unspecific effect on gene expression.Figure 6.

Bottom Line: Here we show that CryB interacts with the C-terminal domain of AppA and modulates the binding of AppA to the transcriptional repressor PpsR in a light-dependent manner.Consequently, binding of the transcription factor PpsR to its DNA target is affected by CryB.These results elucidate for the first time how a bacterial cryptochrome affects gene expression.

View Article: PubMed Central - PubMed

Affiliation: Institut für Mikrobiologie und Molekularbiologie, Universität Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany.

ABSTRACT
The expression of photosynthesis genes in the facultatively photosynthetic bacterium Rhodobacter sphaeroides is controlled by the oxygen tension and by light quantity. Two photoreceptor proteins, AppA and CryB, have been identified in the past, which are involved in this regulation. AppA senses light by its N-terminal BLUF domain, its C-terminal part binds heme and is redox-responsive. Through its interaction to the transcriptional repressor PpsR the AppA photoreceptor controls expression of photosynthesis genes. The cryptochrome-like protein CryB was shown to affect regulation of photosynthesis genes, but the underlying signal chain remained unknown. Here we show that CryB interacts with the C-terminal domain of AppA and modulates the binding of AppA to the transcriptional repressor PpsR in a light-dependent manner. Consequently, binding of the transcription factor PpsR to its DNA target is affected by CryB. In agreement with this, all genes of the PpsR regulon showed altered expression levels in a CryB deletion strain after blue-light illumination. These results elucidate for the first time how a bacterial cryptochrome affects gene expression.

Show MeSH
Related in: MedlinePlus