Abstract
ABSTRACTPurple nonsulfur bacteria adapt their physiology to a wide variety of environmental conditions often through the control of transcription. One of the main transcription factors involved in controlling expression of the Rhodobacter capsulatus photosystem is CrtJ, which functions as an aerobic repressor of photosystem genes. Recently, we reported that a vitamin B12 binding antirepressor of CrtJ called AerR is required for anaerobic expression of the photosystem. However, the mechanism whereby AerR regulates CrtJ activity is unclear. In this study, we used a combination of next-generation sequencing and biochemical methods to globally identify genes under control of CrtJ and the role of AerR in controlling this regulation. Our results indicate that CrtJ has a much larger regulon than previously known, with a surprising regulatory function under both aerobic and anaerobic photosynthetic growth conditions. A combination of in vivo chromatin immunoprecipitation-DNA sequencing (ChIP-seq) and ChIP-seq and exonuclease digestion (ChIP-exo) studies and in vitro biochemical studies demonstrate that AerR forms a 1:2 complex with CrtJ (AerR-CrtJ2) and that this complex binds to many promoters under photosynthetic conditions. The results of in vitro and in vivo DNA binding studies indicate that AerR-CrtJ2 anaerobically forms an extended interaction with the bacteriochlorophyll bchC promoter to relieve repression by CrtJ. This is contrasted by aerobic growth conditions where CrtJ alone functions as an aerobic repressor of bchC expression. These results indicate that the DNA binding activity of CrtJ is modified by interacting with AerR in a redox-regulated manner and that this interaction alters CrtJ’s function.
Highlights
IMPORTANCE Photoreceptors control a wide range of physiology often by regulating downstream gene expression in response to light absorption via a bound chromophore
This study shows that a direct interaction between the vitamin B12 binding photoreceptor AerR with CrtJ modulates CrtJ binding to DNA and importantly, the regulatory outcome of gene expression, as shown here with photosystem promoters
Under aerobic growth conditions (Table S1), the vast majority of differentially expressed genes (DEGs) (37 out of 54 total genes) are those involved in synthesis of the photosystem, such as the bch and crt genes that code for enzymes involved in bacteriochlorophyll and carotenoid synthesis, respectively, as well as the puf and puc genes that code for light-harvesting and reaction center structural components of the photosystem
Summary
IMPORTANCE Photoreceptors control a wide range of physiology often by regulating downstream gene expression in response to light absorption via a bound chromophore. The transcription factors FnrL, RegA, and CrtJ appear to be the main regulators that R. capsulatus uses to control an aerobic-anaerobic metabolic switch [2,3,4,5,6] Among these three transcription factors, CrtJ (called PpsR in some species [7]) was thought to have the narrowest regulon and to play a role in aerobically repressing many photosystem genes such as bch (bacteriochlorophyll), crt (carotenoid), and puc (lightharvesting complex II) [6, 8]. In R. capsulatus, it was recently shown that light controls the activity of CrtJ via the blue-light-absorbing antirepressor AerR that uses vitamin B12 for blue-light absorption [20, 21] Loss of these photoreceptors results in severe PpsR/CrtJ-mediated reduction in photosystem synthesis, leading to a model in which these photoreceptors function as antirepressors [18, 20, 21]. The ability of these photoreceptors to impede PpsR/CrtJ binding to target promoters has not been directly addressed in vivo
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
