Functions of the Duplicated hik31 Operons in Central Metabolism and Responses to Light, Dark, and Carbon Sources in Synechocystis sp. Strain PCC 6803

Abstract

There are two closely related hik31 operons involved in signal transduction on the chromosome and the pSYSX plasmid in the cyanobacterium Synechocystis sp. strain PCC 6803. We studied the growth, cell morphology, and gene expression in operon and hik mutants for both copies, under different growth conditions, to examine whether the duplicated copies have the same or different functions and gene targets and whether they are similarly regulated. Phenotype analysis suggested that both operons regulated common and separate targets in the light and the dark. The chromosomal operon was involved in the negative control of autotrophic events, whereas the plasmid operon was involved in the positive control of heterotrophic events. Both the plasmid and double operon mutant cells were larger and had division defects. The growth data also showed a regulatory role for the chromosomal hik gene under high-CO 2 conditions and the plasmid operon under low-O 2 conditions. Metal stress experiments indicated a role for the chromosomal hik gene and operon in mediating Zn and Cd tolerance, the plasmid operon in Co tolerance, and the chromosomal operon and plasmid hik gene in Ni tolerance. We conclude that both operons are differentially and temporally regulated. We suggest that the chromosomal operon is the primarily expressed copy and the plasmid operon acts as a backup to maintain appropriate gene dosages. Both operons share an integrated regulatory relationship and are induced in high light, in glucose, and in active cell growth. Additionally, the plasmid operon is induced in the dark with or without glucose. Bacteria use several devices to monitor their environment and coordinate appropriate adaptive changes to maximize survival. These include chemotaxis receptors, sigma factors, Ser/Thr protein kinases, and two-component systems (2CSs) (25). The prototypical 2CS consists of a histidine kinase (Hik) sensor that is a transmembrane protein and a response regulator (Rre) that usually binds to DNA and acts as a transcription factor, either activating or repressing the target genes or both. Each protein has two or more domains that perform the various functions and participate in phosphotransfer reactions and can be classified into different types (3,7,8,42). Higher-order 2CSs can have a more complex interaction with combinations of domains and cross talk between different partner 2CSs (7).Signal transduction systems in the freshwater model cyanobacterium Synechocystis sp. strain PCC 6803 (here Synechocystis) are important for sensing, responding to, and adapting to different environmental changes. The Synechocystis genome includes about 47 Hik proteins and 45 Rre proteins, and these make up Ͼ2.5% of the genome. Although most of these are located on the chromosome, 3 each of the Hik proteins and Rre proteins are found on plasmids pSYSX and pSYSM. Unlike in other bacteria, the positions of these genes are scattered throughout the genome, and only 14 sets or 32 open reading frames are in close proximity to each other. The domains of the...

Pathway-Level Acceleration of Glycogen Catabolism by a Response Regulator in the Cyanobacterium Synechocystis Species PCC 6803

“…5) seems to be due to aberrant sugar catabolism, which has been demonstrated by several mutants in Synechocystis 6803 (Osanai et al, 2005Singh and Sherman, 2005;Kahlon et al, 2006;Nagarajan et al, 2012).…”

The CopRS Two-Component System Is Responsible for Resistance to Copper in the Cyanobacterium Synechocystis sp. PCC 6803

“…It is also anticipated that this excess of free copper could be detected and a response similar the one observed here could be launched to detoxify this copper. The proteins studied here are only conserved in some cyanobacteria (Nagarajan et al, 2012;J. GinerLamia, L. López-Maury, and F.J. Florencio, unpublished data), and therefore the response in photosynthetic eukaryotes is likely mediated by a different set of regulatory proteins and effectors, in the same way the petE to petJ switch is conserved between cyanobacteria and Chlamydomonas but the regulatory mechanisms are not (Merchant and Bogorad, 1986;Zhang et al, 1992;Merchant et al, 2006).…”

“…domain that is present in conserved proteins in several other cyanobacteria (Nagarajan et al, 2012) and bacteria, but the function of proteins containing the Duf305 domain has not been reported. CopM contained an elevated number of Met and His residues and a signal peptide that will target it to the periplasmic and/or thylakoid compartment.…”

“…The CopRS two-component system (previously known as Hik31-Rre34) was reported as affecting Synechocystis cell growth under mixotrophic and heterotrophic conditions (Kahlon et al, 2006;Nagarajan et al, 2012), and also in the regulation of the response to low-oxygen conditions (Summerfield et al, 2011). Even more, their mutants lack the expression of icfG, a gene essential for Glc metabolism (Kahlon et al, 2006).…”

Translating Divergent Environmental Stresses into a Common Proteome Response through Hik33 in a Model Cyanobacterium

“…In early gel-based proteomics studies, the relatively low resolution and low throughput nature of this technique limit the analyses to only high abundance proteins (34), which also prevents the identification of the majority of proteins of plasmid origin because they are usually low abundant (33,34). Though the functional significance of these upregulated proteins of plasmid origin is largely unknown, it is conceivable to presume they could complement the functions of some repressed proteins of chromosome origin, as previously observed for the hik31 operon on the plasmid pSYSX (102,103). However, in WT Synechocystis whether these proteins are also stress-inducible and functional in stress acclimation remain to be investigated.…”