Early steps in carotenoid biosynthesis: sequences and transcriptional analysis of the crtI and crtB genes of Rhodobacter sphaeroides and overexpression and reactivation of crtI in Escherichia coli and R. sphaeroides

The roles of oxygen and light on the regulation of photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1 have been well studied over the past 50 years. More recently, the effects of oxygen and light on gene regulation have been shown to involve the interacting redox chains present in R. sphaeroides under diverse growth conditions, and many of the redox carriers comprising these chains have been well studied. However, the expression patterns of those genes encoding these redox carriers, under aerobic and anaerobic photosynthetic growth, have been less well studied. Here, we provide a transcriptional analysis of many of the genes comprising the photosynthesis lifestyle, including genes corresponding to many of the known regulatory elements controlling the response of this organism to oxygen and light. The observed patterns of gene expression are evaluated and discussed in light of our knowledge of the physiology of R. sphaeroides under aerobic and photosynthetic growth conditions. Finally, this analysis has enabled to us go beyond the traditional patterns of gene expression associated with the photosynthesis lifestyle and to consider, for the first time, the full complement of genes responding to oxygen, and variations in light intensity when growing photosynthetically. The data provided here should be considered as a first step in enabling one to model electron flow in R. sphaeroides 2.4

Section: Effect Of Oxygen and Light On R Sphaeroides Transcriptomementioning

confidence: 99%

Effects of Oxygen and Light Intensity on Transcriptome Expression in Rhodobacter sphaeroides 2.4.1

Roh

Smith

Kaplan

2004

“…Such secondary effects could include destabilization of other pigment-protein complexes. Examples include coupled transcription of crtI and crtB in Rhodobacter sphaeroides and its role in the assembly of light-harvesting complex 2 (38).…”

Section: Modification Of Carotenoid Biosynthesis Pathway In Synechocymentioning

confidence: 99%

Construction and Characterization of Genetically Modified Synechocystis sp. PCC 6803 Photosystem II Core Complexes Containing Carotenoids with Shorter π-Conjugation than β-Carotene

Bautista

Tracewell

Schlodder

et al. 2005

␤-Carotene has been identified as an intermediate in a secondary electron transfer pathway that oxidizes Chl Z and cytochrome b 559 in Photosystem II (PS II) when normal tyrosine oxidation is blocked. To test the redox function of carotenoids in this pathway, we replaced the -carotene desaturase gene (zds) or both the zds and phytoene desaturase (pds) genes of Synechocystis sp. PCC 6803 with the phytoene desaturase gene (crtI) of Rhodobacter capsulatus, producing carotenoids with shorter conjugated -electron systems and higher reduction potentials than ␤-carotene. The PS II core complexes of both mutant strains contain approximately the same number of chlorophylls and carotenoids as the wild type but have replaced ␤-carotene (11 double bonds), with neurosporene (9 conjugated double bonds) and ␤-zeacarotene (9 conjugated double bonds and 1 ␤-ionylidene ring). The presence of the ring appears necessary for PS II assembly. Visible and near-infrared spectroscopy were used to examine the light-induced formation of chlorophyll and carotenoid radical cations in the mutant PS II core complexes at temperatures from 20 to 160 K. At 20 K, a carotenoid cation radical is formed having an absorption maximum at 898 nm, an 85 nm blue shift relative to the ␤-carotene radical cation peak in the WT, and consistent with the formation of the cation radical of a carotenoid with 9 conjugated double bonds. The ratio of Chl ؉ /Car ؉ is higher in the mutant core complexes, consistent with the higher reduction potential for Car ؉ . As the temperature increases, other carotenoids become accessible to oxidation by P 680A carotenoid molecule is an extended polyene chain with a variety of end groups and has been thought of as a "molecular wire," because, in the one-electron oxidized form, or carotenoid radical cation, the hole is delocalized over the entire conjugated -system. Carotenoid radical cations have recently been observed in several photosynthetic pigmentprotein complexes, including PS II, 3 bacterial light-harvesting complexes LHC II, and recently in plant PsbS where they may have a role in non-photochemical energy quenching (1). Among photosynthetic reaction centers, carotenoid photooxidation is unique to PS II, which uses light energy to catalyze the oxidation of water to molecular oxygen. The process of water oxidation involves highly oxidizing species that can also oxidize a carotenoid molecule. Carotenoid radical cations have been identified as intermediates in the secondary electron transport pathway of PS II (2-6).Detergent-solubilized PS II core complexes contain up to 25 different integral membrane and extrinsic polypeptide subunits, including the D1/D2 complex and light-harvesting pigment-protein complexes CP43 (PsbC) and CP47 (PsbB). Light energy is absorbed by the chlorophyll-containing light-harvesting antenna and transferred to the primary donor chlorophyll(s) coordinated by the D1/D2 polypeptides. The term "PS II reaction centers" describes a structure that includes the D1 and D2 polypeptides, cytochrome b 559 (Cyt b ...

“…One class, represented by the bchC promoters of R. capsulatus and Rhodobacter sphaeroides and by the R. sphaeroides puc promoter, contains two CrtJ recognition palindromes, one of which spans the Ϫ35 and the other the Ϫ10 -70 recognition sequences (4 -8). The other class, represented by the R. capsulatus puc and crtI promoters and by the R. sphaeroides crtI promoter, has only a single CrtJ palindrome that is near or overlapping with the Ϫ10 or Ϫ35 regions (9,10,11). It is not clear why some promoters contain only one palindrome and others contain two.…”

mentioning

confidence: 99%

Aerobic Repression of the Rhodobacter capsulatus bchCPromoter Involves Cooperative Interactions between CrtJ Bound to Neighboring Palindromes

Ponnampalam

Elsen

Bauer

1998

Previous studies demonstrated that bacteriochlorophyll, carotenoid, and light harvesting gene expression in Rhodobacter capsulatus is repressed under aerobic growth conditions by the repressor CrtJ. Isolated CrtJ is known to bind to the palindrome TGTN 12 ACA, which is present in two copies in the bchC promoter, one of which spans the ؊35 and the other the ؊10 -70 recognition sequences. In this study, we demonstrate that CrtJ binds to the two palindromic sites in the bchC promoter in a cooperative manner. The level of cooperativity of CrtJ binding to the ؊35 palindrome was shown to be 26-fold. A distance of 8 base pairs between the two palindromic sites was shown to be critical for cooperative binding, as evidenced by the disruption of binding that resulted when ؉6 and ؉11 base pairs were inserted between the palindromes.