Comparative studies of the AHP histidine-containing phosphotransmitters implicated in His-to-Asp phosphorelay in Arabidopsis thaliana

The evolutionarily-conserved histidine to aspartate (His-to-Asp) phosphorelay signal transduction is common in both prokaryotes and eukaryotes. Such a phosphorelay system is generally made up of 'a histidine (His)-kinase', 'a histidine-containing phosphotransmitter (HPt)', and 'a phospho-accepting response regulator (RR)'. In general, an HPt factor acts as an intermediate in a given multistep His-to-Asp phosphorelay. In Arabidopsis thaliana, this model higher plant has five genes (named AHP1 to AHP5), each of which seems to encode an HPt factor. Recent studies suggested that the His-to-Asp phosphorelay involving the AHP factors is at least partly implicated in signal transduction in response to cytokinin (a plant hormone). Nevertheless, the properties of AHPs have not yet been fully clarified. Here we did comparative studies of all the AHP factors, in terms of (i) expression profiles in plants, (ii) intracellular localization, (iii) ability to acquire a phosphoryl group in vitro, and (iv) ability to interact with the downstream components, ARRs (Arabidopsis response regulators). The results of this study provided us with a comprehensive view at the molecular level for understanding the functions of the AHP phosphotransmitters in the His-to-Asp phosphorelay.     

Compilation and Characterization of Histidine-Containing Phosphotransmitters Implicated in His-to-Asp Phosphorelay in Plants: AHP Signal Transducers of Arabidopsis thaliana

Histidine (His)-to-Aspartate (Asp) phosphorelay signal transduction systems are generally made up of a “sensor histidine (His)-kinase”, a “response regulator”, and a “histidine-containing phosphotransmitter (HPt)”. In the higher plant, Arabidopsis thaliana, results from recent intensive studies suggested that the His-to-Asp phosphorelay mechanism is at least partly responsible for propagation of environmental stimuli, such as phytohormones (e.g. ethylene and cytokinin). Here we compiled the members of the HPt family of phosphotransmitters in Arabidopsis thaliana (AHP- series, Arabidopsis HPt phosphotransmitters), based on both database and experimental analyses, in order to provide a comprehensive basis at the molecular level for understanding the function of the AHP phosphotransmitters that are implicated in the His-to-Asp phosphorelay of higher plants.     

Compilation and characterization of histidine-containing phosphotransmitters implicated in His-to-Asp phosphorelay in plants: AHP signal transducers of Arabidopsis thaliana

Histidine (His)-to-Aspartate (Asp) phosphorelay signal transduction systems are generally made up of a "sensor histidine (His)-kinase", a "response regulator", and a "histidine-containing phosphotransmitter (HPt)". In the higher plant, Arabidopsis thaliana, results from recent intensive studies suggested that the His-to-Asp phosphorelay mechanism is at least partly responsible for propagation of environmental stimuli, such as phytohormones (e.g. ethylene and cytokinin). Here we compiled the members of the HPt family of phosphotransmitters in Arabidopsis thaliana (AHP-series, Arabidopsis HPt phosphotransmitters), based on both database and experimental analyses, in order to provide a comprehensive basis at the molecular level for understanding the function of the AHP phosphotransmitters that are implicated in the His-to-Asp phosphorelay of higher plants.     

Cellular localization of the signaling components of Arabidopsis His-to-Asp phosphorelay.

In the higher plant, Arabidopsis thaliana, histidine-to-aspartate (His-to-Asp) phosphorelay signal transduction systems play crucial roles in propagation of environmental stimuli, including plant hormones. This plant has 11 sensor His-kinases, 5 histidine-containing phosphotransfer (HPt) factors (AHPs), and 20 response regulators (ARRs). To gain new insight into the functions of these phosphorelay components, their intracellular localization was examined with use of GFP-fusion proteins, constructed for certain representatives of HPt factors (AHP2) and type-A and type-B ARRs (ARR6/ARR7 and ARR10, respectively). The results showed that AHP2 is mainly located in the cytoplasmic space, while both the types of ARRs have an ability to enter preferentially into the nuclei, if not exclusively. Together with the results from an in vitro phosphorelay assay with AHP2 and ARRs, these results are discussed, in terms of a geneal framework of the Arabidopsis His-to-Asp phosphorelay network.     

l-Serine Production Improved by Analogue-resistant Mutants of a Methanol-utilizing Bacterium

In the higher plant, Arabidopsis thaliana, histidine-to-aspartate (His-to-Asp) phosphorelay signal transduction systems play crucial roles in propagation of environmental stimuli, including plant hormones. This plant has 11 sensor His-kinases, 5 histidine-containing phosphotransfer (HPt) factors (AHPs), and 20 response regulators (ARRs). To gain new insight into the functions of these phosphorelay components, their intracellular localization was examined with use of GFP-fusion proteins, constructed for certain representatives of HPt factors (AHP2) and type-A and type-B ARRs (ARR6/ARR7 and ARR10, respectively). The results showed that AHP2 is mainly located in the cytoplasmic space, while both the types of ARRs have an ability to enter preferentially into the nuclei, if not exclusively. Together with the results from an in vitro phosphorelay assay with AHP2 and ARRs, these results are discussed, in terms of a geneal framework of the Arabidopsis His-to-Asp phosphorelay network.     

Histidine-containing phosphotransfer (HPt) signal transducers implicated in His-to-Asp phosphorelay in Arabidopsis

His to Asp phosphorelay signal transduction mechanisms involve three types of widespread signaling components: a sensor His-kinase, a response regulator, and a histidine-containing phosphotransfer (HPt) domain. In Arabidopsis, several sensor His-kinases have recently been discovered (e.g., ETR1 and CKI1) through extensive genetic studies. Furthermore, a recent search for response regulators in this higher plant revealed that it possesses a group of response regulators (ARR-series), each of which exhibits the phospho-accepting receiver function. However, no signal transducer containing the HPt domain has been reported. Here we identify three distinct Arabidopsis genes (AHP1 to AHP3), each encoding a signal transducer containing a HPt domain. Both in vivo and in vitro evidence that each AHP can function as a phospho-transmitting HPt domain with an active histidine site was obtained by employing both the Escherichia coli and yeast His-Asp phosphorelay systems. It was demonstrated that AHP1 exhibits in vivo ability to complement a mutational lesion of the yeast YPD1 gene, encoding a typical HPt domain involved in an osmosensing signal transduction. It was also demonstrated that AHPs can interact in vitro with ARRs through the His-Asp phosphotransfer reaction. It was thus suggested that the uncovered sensors-AHPs-ARRs lineups may play important roles in propagating environmental stimuli through the multistep His-Asp phosphorelay in Arabidopsis.     

Biochemical characterization of a putative cytokinin-responsive His-kinase, CKI1, from Arabidopsis thaliana

His-Asp phosphorelays are evolutionary-conserved powerful biological tactics for intracellular signal transduction. Such a phosphorelay is generally made up of "sensor histidine (His)-kinases", "response regulators", and "histidine-containing (HPt) phosphotransmitters". Results from recent intensive studies suggested that in the higher plant Arabidopsis thaliana, His-Asp phosphorelays may be widely used for propagating environmental stimuli, such as phytohormones (e.g., ethylene and cytokinin). In this study, we characterized, in vitro, the putative cytokinin-responsive CKI1 His-kinase, in terms of His-Asp phosphorelays. It was demonstrated for the first time that the receiver domain in this sensor exhibits a strong phosphohistidine phosphatase activity toward some Arabidopsis HPt phosphotransmitters (AHP1 and AHP2), suggesting the functional importance of the receiver domain for a resumed interaction of the sensor His-kinase with other His-Asp phosphorelay components.     

Two types of putative nuclear factors that physically interact with histidine-containing phosphotransfer (Hpt) domains, signaling mediators in His-to-Asp phosphorelay, in Arabidopsis thaliana

The higher plant, Arabidopsis thaliana, has a large number of genes, each of which encodes a component of His-to-Asp phosphorelay signal transduction systems. One type of such signal transducers are the histidine-containing phosphotransmitters (termed AHPs), which presumably mediate His-to-Asp phosphorelay. Here we attempted to isolate a factor or factors that interact with AHP1, AHP2 and AHP3 by means of a yeast two-hybrid system. This allowed us to identify two types of nuclear-localizing proteins. They are the members of the type-B family of response regulators (specifically, ARR1, APP2 and ARR10), and a novel protein named TCP10. The binding of ARR1 to AHP2 was also confirmed by in vitro binding assays. Moreover, dephosphorylation of AHP2 was observed in a manner dependent on ARR in vitro. A subset of AHPs appeared to also interact with a protein that contains a TCP domain, a recently proposed basic helix-loop-helix motif. Because several factors carrying the TCP domain have been implicated in the regulation of growth and development in lateral organs, the binding of TCP10 to this subset of AHPs suggests a possible linkage between the His-to-Asp phosphorelay systems and plant growth regulation.     

Spy1, a histidine-containing phosphotransfer signaling protein, regulates the fission yeast cell cycle through the Mcs4 response regulator

Common histidine-to-aspartate (His-to-Asp) phosphorelay signaling systems involve three types of signaling components: a sensor His kinase, a response regulator, and a histidine-containing phosphotransfer (HPt) protein. In the fission yeast Schizosaccharomyces pombe, two response regulators, Mcs4 and Prr1, have been identified recently, and it was shown that they are involved in the signal transduction implicated in stress responses. Furthermore, Mcs4 appears to be involved in mitotic cell-cycle control. However, neither the HPt phosphotransmitter nor His kinase has been characterized in S. pombe. In this study, we identified a gene encoding an HPt phosphotransmitter, named Spy1 (S. pombe YPD1-like protein). The spy1(+) gene showed an ability to complement a mutational lesion of the Saccharomyces cerevisiae YPD1 gene, which is involved in an osmosensing signal transduction. The result from yeast two-hybrid analysis indicated that Spy1 interacts with Mcs4. To gain insight into the function of Spy1, a series of genetic analyses were conducted. The results provided evidence that Spy1, together with Mcs4, plays a role in regulation of the G(2)/M cell cycle progression. Spy1-deficient cells appear to be precocious in the entry to M phase. In the proposed model, Spy1 modulates Mcs4 in a negative manner, presumably through a direct His-to-Asp phosphorelay, operating upstream of the Sty1 mitogen-activated protein kinase cascade.     

An Arabidopsis histidine-containing phosphotransfer (HPt) factor implicated in phosphorelay signal transduction: overexpression of AHP2 in plants results in hypersensitiveness to cytokinin

Histidine-containing phosphotransfer (HPt) factors from Arabidopsis thaliana, designated as AHPs, function most likely in concert with histidine (His)-kinases (HKs) and response regulators (RRs) in certain multistep histidine (His)-->aspartate (Asp) phosphorelays that are involved in the signal transduction mechanisms, by which plant cells appear to respond to certain hormonal stimuli, including cytokinin. Although some previous in vitro results from studies on Arabidopsis AHPs (AHP1 to AHP5) supported this hypothesis, it has not yet been proven. To this end, here we constructed transgenic plants that contained the AHP2 protein in a considerably higher amount than in wild-type plants. Such AHP2-overexpressing young seedlings were examined in comparison with wild-type plants, with special reference to hormone responses; particularly, their inhibitory effects on root elongation of plants grown on agar-plates, and also hypocotyl elongation of etiolated seedlings grown in the dark. The results of this study suggested that AHP2-overexpressing plants showed a characteristic phenotype of cytokinin-hypersensitive. These in vivo observations were best interpreted by assuming that the AHP factor(s) is somehow implicated, if not directly, in a cytokinin-mediated His-->Asp phosphorelay signaling in Arabidopsis.     

Genetic analysis of the His-to-Asp phosphorelay implicated in mitotic cell cycle control: involvement of histidine-kinase genes of Schizosaccharomyces pombe.

Common histidine-to-aspartate (His-to-Asp) phosphorelay signaling systems involve three types of signaling components: a sensor His-kinase, a response regulator, and a histidine-containing phosphotransfer (HPt) protein. In the fission yeast Schizosaccharomyces pombe, two response regulators, Mcs4 and Prr1, have been identified, and it was shown that they are involved in signal transduction in stress responses. Furthermore, Mcs4 and Prr1 appear to be involved in mitotic cell-cycle control and meiosis, respectively. Recently we have identified Spy1 (also known as Mpr1), which encodes an HPt phosphotransmitter, and reported that Spy1, together with Mcs4, plays a role in cell cycle regulation. In this study, we identified and characterized three genes encoding histidine kinase, named Phk1, Phk2, and Phk3 (S. pombe histidine kinase) (also referred as Mak2, Mak3, and Mak1, respectively). Deletion of individual kinase genes has no apparent phenotypes but multiple deletion of these kinases showed the same phenotype of Spyl (Mpr1)-deficient cells, indicating precocious entry into M phase. These results indicated that three histidine kinases that work upstream of the HPt-transmitter, Spy1 (Mpr1), have a redundant function in cell cycle control.     

Screening of Dextranase Producing Microorganisms

Common histidine-to-aspartate (His-to-Asp) phosphorelay signaling systems involve three types of signaling components: a sensor His-kinase, a response regulator, and a histidine-containing phosphotransfer (HPt) protein. In the fission yeast Schizosaccharomyces pombe, two response regulators, Mcs4 and Prr1, have been identified, and it was shown that they are involved in signal transduction in stress responses. Furthermore, Mcs4 and Prr1 appear to be involved in mitotic cellcycle control and meiosis, respectively. Recently we have identified Spy1 (also known as Mpr1), which encodes an HPt phosphotransmitter, and reported that Spy1, together with Mcs4, plays a role in cell cycle regulation. In this study, we identified and characterized three genes encoding histidine kinase, named Phk1, Phk2, and Phk3 (S. pombe histidine kinase) (also referred as Mak2, Mak3, and Mak1, respectively). Deletion of individual kinase genes has no apparent phenotypes but multiple deletion of these kinases showed the same phenotype of Spy1 (Mpr1)-deficient cells, indicating precocious entry into M phase. These results indicated that three histidine kinases that work upstream of the HPt-transmitter, Spy1 (Mpr1), have a redundant function in cell cycle control.     

Compilation and characterization of Arabidopsis thaliana response regulators implicated in His-Asp phosphorelay signal transduction.

His-Asp phosphorelays are evolutionary-conserved powerful biological tactics for intracellular signal transduction. Such a phosphorelay is generally made up of "sensor histidine (His)-kinases", "response regulators", and "histidine-containing (HPt) phosphotransmitters". In the higher plant, Arabidopsis thaliana, results from recent intensive studies suggested that His-Asp phosphorelays may be widely used for propagating environmental stimuli, such as phytohormones (e.g., ethylene and cytokinin). In this study, we first inspected extensively the occurrence of Arabidopsis response regulators in order to compile and characterize them. The results showed that this higher plant has, at least, 14 members of the family of response regulators that can be classified into two distinct subtypes (type-A and type-B), as judged from their structural designs, biochemical properties, and expression profiles. Comparative studies were conducted for each representative (ARR3 and ARR4 for type-A, and ARR10 for type-B). It was suggested that expression of the type-A response regulator is cytokinin-inducible, while that of the type-B response regulator appears to be not. Results from yeast two-hybrid analyses suggested that the type-B response regulator may have an ability to stably interact with a set of HPt phosphotransmitters (AHPs). These and other results will be discussed with special reference to the His-Asp phosphorelay signaling network in Arabidopsis thaliana.     

The SixA phospho-histidine phosphatase modulates the ArcB phosphorelay signal transduction in Escherichia coli

The Escherichia coli SixA protein is the first discovered prokaryotic phospho-histidine phosphatase, which was implicated in a His-to-Asp phosphorelay. The sixA gene was originally identified as the one that interferes with, at its multi-copy state, the cross-phosphorelay between the histidine-containing phosphotransmitter (HPt) domain of the ArcB anaerobic sensor and its non-cognate OmpR response regulator. Nevertheless, no evidence has been provided that the SixA phosphatase is indeed involved in a signaling circuitry of the authentic ArcB-to-ArcA phosphorelay in a physiologically meaningful manner. In this study, a SixA-deficient mutant was characterized with special reference to the ArcB signaling, which allows E. coli cells to respond to not only external oxygen, but also certain anaerobic respiratory conditions. Here evidence is provided for the first time that the SixA phosphatase is a crucial regulatory factor that is involved in the ArcB signaling, particularly, under certain anaerobic respiratory growth conditions. We propose a novel mechanism, involving an HPt domain and a phospho-histidine phosphatase, by which a given multi-step His-to-Asp signaling can be modulated.     

The <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> response regulator ARR22 is a putative AHP phospho-histidine phosphatase expressed in the chalaza of developing seeds

Background  

The Arabidopsis response regulator 22 (ARR22) is one of two members of a recently defined novel group of two-component system (TCS) elements. TCSs are stimulus perception and response modules of prokaryotic origin, which signal by a His-to-Asp phosphorelay mechanism. In plants, TCS regulators are involved in hormone response pathways, such as those for cytokinin and ethylene. While the functions of the other TCS elements in Arabidopsis, such as histidine kinases (AHKs), histidine-containing phosphotransfer proteins (AHPs) and A-type and B-type ARRs are becoming evident, the role of ARR22 is poorly understood.     

Roles of the His-Asp phosphorelay signal transduction system in controlling cell growth and development in Aspergillus nidulans

The His-Asp phosphorelay signal transduction system has been identified in most organisms, including bacteria, yeasts, fungi, and plants, except for animals. This system is important in adaptation to stress, control of cell growth, and induction of development in response to environmental changes. On the basis of genomic information, it has been found that Aspergillus nidulans, a model species of fungi, includes 15 histidine kinases (HKs), one histidine-containing phosphotransmitter protein (HPt), and four response regulators (RRs) as factors related to the signal transduction system. In this review, it is explain that the His-Asp phosphorelay system is important in controlling cell growth (responses to fungicides, the induction of asexual and sexual development, and so on) under different growth conditions with reference to A. nidulans.     

Genome-wide comparison of the His-to-Asp phosphorelay signaling components of three symbiotic genera of Rhizobia.

Histidine-to-aspartate (His-Asp) phosphorelay (or two-component) systems are very common signal transduction mechanisms that are implicated in a wide variety of cellular responses to environmental stimuli. The His-Asp phosphorelay components include "sensor histidine kinase (HK)", "phosphotransfer intermediate (HPt)", and "response regulator (RR)". With special reference to three bacterial species (Mesorhizobium loti, Bradyrhizobium japonicum, Sinorhizobium meliloti), each of which belongs to a different genera of Rhizobia, here we attempted to compile all of the His-Asp phosphorelay components in order to reveal a comparative genome-wide overview as to the His-Asp phosphorelay. It was revealed that M. loti has 47 HKs, 1 HPts, and 58 RRs; B. japonicum has 80 HKs, 3 HPts, and 91 RRs; whereas S. meliloti has 40 HKs, 1 HPt, and 58 RRs. These His-Asp phosphorelay components were extensively compiled and characterized. The resulting overview as to the His-Asp phosphorelay of Rhizobia will provide us with a basis for understanding of the fundamental mechanisms underlying interactions between plants and microorganisms (including symbiosis), as well as nitrogen fixation.