Discrete Redox Signaling Pathways Regulate Photosynthetic Light-Harvesting and Chloroplast Gene Transcription

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Probing the nucleotide-binding activity of a redox sensor: two-component regulatory control in chloroplasts

Two-component signal transduction systems mediate adaptation to environmental changes in bacteria, plants, fungi, and protists. Each two-component system consists of a sensor histidine kinase and a response regu- lator. Chloroplast sensor kinase (CSK) is a modified sensor histidine kinase found in chloroplasts—photosynthetic organelles of plants and algae. CSK regulates the tran- scription of chloroplast genes in response to changes in photosynthetic electron transport. In this study, the full- length and truncated forms of Arabidopsis CSK proteins were overexpressed and purified in order to characterise their kinase and redox sensing activities. Our results show that CSK contains a modified kinase catalytic domain that binds ATP with high affinity and forms a quinone adduct that may confer redox sensing activity

Oligomeric states in sodium ion-dependent regulation of cyanobacterial histidine kinase-2

Two-component signal transduction systems (TCSs) consist of sensor histidine kinases and response regulators. TCSs mediate adaptation to environmental changes in bacteria, plants, fungi and protists. Histidine kinase 2 (Hik2) is a sensor histidine kinase found in all known cyanobacteria and as chloroplast sensor kinase in eukaryotic algae and plants. Sodium ions have been shown to inhibit the autophosphorylation activity of Hik2 with precedes phosphoryl transfer to response regulators, but the mechanism of inhibition has not been determined. We report on the mechanism of Hik2 activation and inactivation probed by chemical cross-linking and size exclusion chromatography together with direct visualisation of the kinase using negative-stain transmission electron microscopy of single particles. We show that the functional form of Hik2 is a higher-order oligomer such as a hexamer or octamer. Increased NaCl concentration converts the active hexamer into an inactive tetramer. The action of NaCl appears to be confined to the Hik2 kinase domain

Increased expression of the interleukin-1 receptor-associated kinase (IRAK)-1 is associated with adipose tissue inflammatory state in obesity

Figure S2. Comparison of IRAK-1 gene and protein expression in the adipose tissue. The gene and protein expression of IRAK-1 in non-diabetic obese, overweight, and lean adipose tissue samples, 5 each, were determined by using real-time RT-PCR and immunohistochemistry, respectively, as described in Patients and Methods. The relative mRNA expression was measured as fold expression over average of control gene expression taken as 1. The protein expression was measured as intensity which was calculated by using Aperio positive pixel count algorithm software (version 9)

Two-component signalling systems of chloroplasts: function, distribution and evolution

PhD 2008 QMTwo-component signal transduction, comprising sensor kinases and response regulators, is the predominant signalling mechanism in prokaryotes. This signalling system originated in bacteria, and has spread to the eukaryotic domain of life through symbiotic, lateral gene transfer from the bacterial ancestors of chloroplasts and mitochondria. During the course of their evolution, chloroplasts, with the exception of a few instances in non-green algae, appear to have relinquished all genes encoding two-component systems to their eukaryotic host cell nuclei. In green algae and plants, chloroplast genes for two-component systems were neither known nor were chloroplast two-component proteins shown to exist as products of nuclear genes prior to the work described here. This thesis describes the identification and characterisation of a novel two-component sensor kinase in chloroplasts. This Chloroplast Sensor Kinase (CSK) is the product of a nuclear gene in algae and plants. CSK is synthesised in the cytosol of Arabidopsis thaliana and imported into the chloroplast as a protein precursor. CSK is autophosphorylated and couples photosynthetic electron transport to gene transcription in chloroplasts. The identity of the response regulator partner of CSK reveals an unexpected phylogenetic and functional relatedness of CSK with chloroplast two-component systems of non-green algae. Chloroplast two-component systems are likely to be universal in photosynthetic eukaryotes and they persist in chloroplasts as products of nuclear genes even where chloroplast genomes no longer encode them. Chloroplast twocomponent systems have homologues in extant cyanobacterial lineages, indicating their ancient cyanobacterial origin. The persistence of cyanobacterial two-component systems in chloroplasts and their function in coupling photosynthesis with chloroplast gene expression are central to the premise that chloroplasts retain genes whose expression is regulated by the activity of the photosynthetic electron transport chain, using a mechanism conserved from their cyanobacterial ancestors.Queen Mary University of London Postgraduate Research Studentshi

Diversity and Evolution of Sensor Histidine Kinases in Eukaryotes

Histidine kinases (HKs) are primary sensor proteins that act in cell signaling pathways generically referred to as "two component systems" (TCSs). TCSs are among the most widely distributed transduction systems used by both prokaryotic and eukaryotic organisms to detect and respond to a broad range of environmental cues. The structure and distribution of HK proteins are now well documented in prokaryotes but information is still fragmentary for eukaryotes. Here, we have taken advantage of recent genomic resources to explore the structural diversity and the phylogenetic distribution of HKs in the prominent eukaryotic supergroups. Searches of the genomes of 67 eukaryotic species spread evenly throughout the phylogenetic tree of life identified 748 predicted HK proteins. Independent phylogenetic analyses of predicted HK proteins were carried out for each of the major eukaryotic supergroups. This allowed most of the compiled sequences to be categorised into previously described HK groups. Beyond the phylogenetic analysis of eukaryotic HKs, this study revealed some interesting findings: (i) characterisation of some previously undescribed eukaryotic HK groups with predicted functions putatively related to physiological traits; (ii) discovery of HK groups that were previously believed to be restricted to a single kingdom in additional supergroups and (iii) indications that some evolutionary paths have led to the appearance, transfer, duplication, and loss of HK genes in some phylogenetic lineages. This study provides an unprecedented overview of the structure and distribution of HKs in the Eukaryota and represents a first step towards deciphering the evolution of TCS signaling in living organisms

Identification of Genes under Positive Selection Reveals Differences in Evolutionary Adaptation between Brown-Algal Species

Brown algae are an important taxonomic group in coastal ecosystems. The model brown algal species Ectocarpus siliculosus and Saccharina japonica are closely related lineages. Despite their close phylogenetic relationship, they vary greatly in morphology and physiology. To obtain further insights into the evolutionary forces driving divergence in brown algae, we analyzed 3,909 orthologs from both species to identify Genes Under Positive Selection (GUPS). About 12% of the orthologs in each species were considered to be under positive selection. Many GUPS are involved in membrane transport, regulation of homeostasis, and sexual reproduction in the small sporophyte of E. siliculosus, which is known to have a complex life cycle and to occupy a wide range of habitats. Genes involved in photosynthesis and cell division dominated the group of GUPS in the large kelp of S. japonica, which might explain why this alga has evolved the ability to grow very rapidly and to form some of the largest sporophytes. A significant number of molecular chaperones (e.g., heat-shock proteins) involved in stress responses were identified to be under positive selection in both species, potentially indicating their important roles for macroalgae to cope with the relatively variable environment of coastal ecosystems. Moreover, analysis of previously published microarray data of E. siliculosus showed that many GUPS in E. siliculosus were responsive to stress conditions, such as oxidative and hyposaline stress, whereas our RNA-seq data of S. japonica showed that GUPS in this species were most highly expressed in large sporophytes, which supports the suggestion that selection largely acts on different sets of genes in both marcoalgal species, potentially reflecting their adaptation to different ecological niches

Considering Environmental Effects on Porous Concrete Applications: An Experimental Investigation

Urban areas worldwide grapple with ecological disruption due to overpopulation, exacerbated by impermeable concrete surfaces that hinder rainwater absorption, curb plant growth and foster urban heat islands. Innovative porous concrete applications were pioneered in developed countries in recent times, offering alternative solutions albeit with limitations in strength (typically less than 20MPa). These include pavement systems (e.g. sidewalks, bike paths, parking lots), flood control infrastructure, green roofs and decorative / landscaping features. This experimental study investigates engineering properties of porous concrete mixes, suitably designed for harsh climatic conditions, with the incorporation of admixtures. A series of destructive & non-destructive tests were conducted at different ages of the concrete specimens. Test results were analysed and compared to conventional concrete to evaluate the potential benefits of using porous concrete in Scotland. This research makes a valuable contribution to the existing body of knowledge on porous concrete and provides data of direct applicability to designers and contractors so that they make more informed decisions about porous concrete applications, while considering environmental effects

Oligomeric states in sodium ion-dependent regulation of cyanobacterial histidine kinase-2

IMI thanks Queen Mary University of London for a graduate teaching studentship. LW thanks the China Scholarship Council (CSC) and Queen Mary University of London for financial support. SP held a Leverhulme Trust early-career post-doctoral research fellowship. JN is grateful for the continued support of the JST CREST Grant Number JPMJCR13M4, Japan. JFA acknowledges the support of research grant F/07 476/AQ and fellowship EM-2015-068 of the Leverhulme Trust

Transcriptional Control of Photosynthesis Genes: The Evolutionarily Conserved Regulatory Mechanism in Plastid Genome Function

Chloroplast sensor kinase (CSK) is a bacterial-type sensor histidine kinase found in chloroplasts—photosynthetic plastids—in eukaryotic plants and algae. Using a yeast two-hybrid screen, we demonstrate recognition and interactions between: CSK, plastid transcription kinase (PTK), and a bacterial-type RNA polymerase sigma factor-1 (SIG-1). CSK interacts with itself, with SIG-1, and with PTK. PTK also interacts directly with SIG-1. PTK has previously been shown to catalyze phosphorylation of plastid-encoded RNA polymerase (PEP), suppressing plastid transcription nonspecifically. Phospho-PTK is inactive as a PEP kinase. Here, we propose that phospho-CSK acts as a PTK kinase, releasing PTK repression of chloroplast transcription, while CSK also acts as a SIG-1 kinase, blocking transcription specifically at the gene promoter of chloroplast photosystem I. Oxidation of the photosynthetic electron carrier plastoquinone triggers phosphorylation of CSK, inducing chloroplast photosystem II while suppressing photosystem I. CSK places photosystem gene transcription under the control of photosynthetic electron transport. This redox signaling pathway has its origin in cyanobacteria, photosynthetic prokaryotes from which chloroplasts evolved. The persistence of this mechanism in cytoplasmic organelles of photosynthetic eukaryotes is in precise agreement with the CoRR hypothesis for the function of organellar genomes: the plastid genome and its primary gene products are Co-located for Redox Regulation. Genes are retained in plastids primarily in order for their expression to be subject to this rapid and robust redox regulatory transcriptional control mechanism, whereas plastid genes also encode genetic system components, such as some ribosomal proteins and RNAs, that exist in order to support this primary, redox regulatory control of photosynthesis genes. Plastid genome function permits adaptation of the photosynthetic apparatus to changing environmental conditions of light quantity and quality