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) 1448A have been recently sequenced providing a study resource for comparative genomic analysis. A mechanism commonly found in bacteria for signal transduction is the two-component system (TCS) which typically consists of a sensor histidine kinase (HK) and a response regulator (RR).
requires a complex arrange of TCS proteins to act with diverse plant hosts host responses and environmental conditions.
1448A were found to contain a large number of genes encoding TCS proteins and a core of complete TCS proteins were shared between these genomes: 30 putative TCS clusters. 11 orphan HKs. 33 orphan RRs and 16 hybrid HKs. A close analysis of the distribution of genes encoding TCS proteins revealed important differences in TCS proteins among the three
pathovars that may alter to their diverse entertain ranges and association with plant hosts. The identification and analysis of the repertoire of TCS proteins in the genomes of
pathovars constitute a basis for future functional genomic studies of the communicate transduction pathways in this important bacterial phytopathogen.
Bacterial signal transduction pathways sense the cellular external environment and regulate cellular functions in response to environmental signals. A mechanism commonly open in bacteria for signal transduction is the two-component system (TCS). Bacterial TCSs are common components of complex regulatory networks and cascades often associated with global regulation as well as with regulation of virulence. TCS genes are typically located within the same operon encoding two signalling proteins: a transmembrane sensor histidine kinase (HK) and a cytoplasmic response regulator (RR) which may sometimes be carried by a hit polypeptide to create the hybrid HKs []. The mechanism of signal transduction by TCS proteins is based on phosphotransfer reactions between histidine (H) and aspartate (D) residues in highly conserved signalling domains of the HKs and their cognate RRs. TCS proteins have a modular organization which may furnish rise to highly complex structures but the core structures and activities are maintained []. HKs are typically organized as homodimers with two functionally and structurally distinct domains: a highly variable N-terminal extracytoplasmic sensory domain and a more conserved C-terminal cytoplasmic transmitter domain also known as the dimerization/phosphoacceptor domain [,]. The sensor domain varies in length and amino acid sequence from one HK to another conferring specificity for different environmental stimuli. In most HKs the transmitter domain shows high grade conservation especially within a set of six recognizable motifs or boxes designated H. N. F. G1. G2 and G3. In particular the H box contains an invariant H residue that is autophosphorylated in an ATP-dependent manner []. In contrast. CheA-like HKs that answer in chemotaxis lack the sensor domain and differ from other HKs in their domain constitution and organization where the H box of the transmitter domain resides at the N-terminal end of the protein []. LytS-like HKs also differ significantly in their domain architecture from other HKs []. RRs generally include at least two functional domains: a conserved N-terminal receiver domain (REC domain) that is phosphorylated by the HK at a strictly conserved D residue and one or more variable C-terminal create domains []. Modulation of the phosphorylated state of the RR controls either expression of the target genes or cellular behaviour. The principal type of bacterial RRs are transcription factors that adjust gene-expression with DNA-binding helix-turn-helix (HTH) create domains [,,,]. Hybrid HKs contain both a HK transmitter domain and a REC domain in a single large polypeptide and are characterized by multi-step phosphotransfer reactions [,,].
The availability of complete genome sequences for a continually growing number of bacteria has allowed the definitive assessment that TCS proteins are show in almost all bacterial species [,,]. Genomic analyses demonstrate the enormous impact of TCSs on environmental adaptation of bacteria and show a wide variation of HK and RR numbers between different bacterial species [,,,].
have been classified into different pathovars depending on their entertain range among different plant species []. Infection of entertain plants by
involves growth on leaf surfaces as an epiphyte that enters lay leaves through stomata multiplies to large populations in the apoplast and produces disease symptoms [,].
injects effector proteins into the cytoplasm of plant cells by means of the Hrp write III secretion system []. Genome comparisons tell that
species [,] suggesting that in the adaptation to the phytopathogenic lifestyle its genome must have undergone fundamental changes without a reduction in coat. The end genomic sequences of three economically important pathovars of this plant pathogenic bacteria have been determined:
) 1448A []. In these genomes over 10 to 12 % of the genes are dedicated to regulation which may reflect the be for rapid adaptation to the diverse environments encountered during epiphytic growth plant colonization and pathogenesis []. Genome analyses of these
pathovars revealed fewer extracytoplasmic answer (ECF) sigma factors (10 ECF sigma factors) than in related
DC3000 genome sequence allowed the identification of 69 HKs [,] and 71 RRs. 21 of which were hybrid HKs []. In a different study not including CheA-like HKs. 64 HKs were identified in
requires a complex arrange of TCS proteins to act with diverse plant hosts host responses and environmental conditions. The availability of complete genomic sequences of three different
pathovars makes it possible to conduct this comparative genomic study to determine and analyse the TCS proteins of
1448A were identified by searching the complete genome sequences for proteins containing HK and RR domains using Pfam HMM profiles. Four CheA-like HKs in each
genome were identified in BLASTP searches using as template the CheA HK of
pathovar against the genomes of the other two pathovars allowed the identification of additional HKs and RRs. The genomes of
pathovars were found to include large numbers of genes encoding TCS proteins: 68 HKs and 93 RRs in
1448A (Tables and ). The HMM search method used in this work retrieved hybrid HKs as well as RRs (Table ). No TCS proteins were identified on any of the plasmids of
DC3000 have been reported: 69 HKs [,] and 71 RRs. 21 of which were hybrid HKs []; or 64 HKs in a chew over not including CheA-like HKs. 20 of which where hybrid HKs []. Although the be of ECF sigma factors in all three
genomes (10 ECF sigma factors) is only about half that found in other
1448A allowing the identification of gene clusters containing HKs and RRs that constitute putative TCSs (Table ). desire in other bacterial species many
HKs and RRs were encoded by clusters of adjacent genes: 37 putative clusters of complete TCS genes in
1448A (delay ). For the remaining HK or RR genes their furnish genes could not be predicted from genetic organization and therefore they were considered as deprive HKs or RRs. The deprive HKs were 11 in each
genome and the number of genes encoding orphan RRs was very high: 36 in
1448A (Table ). Finally the comparative genomic analysis allowed the identification of a core of complete TCS protein orthologues among the three
pathovars that is composed by 30 putative TCS clusters (HK and RR) (Table ). 11 orphan HKs. 33 orphan RRs (Table ) and 16 hybrid HKs (delay ).
HKs have been classified on the basis of phylogenetic analyses and the sequence relationships of the residues surrounding the H-box [,,,]. Furthermore several new domains with putative biological functions have been described in HKs and domain architecture has proven particularly informative for analysing multi-domain proteins involved in signal transduction [,,,]. The phylogenetic analysis and examination of the region around the H box of
HKs showed that three of the five major HK types open in
However the LytS-like HK FimS/AlgZ and HKs containing GAF domains did not cluster within any of the defined HK types of
[] and formed two separate HK groups: LytS-like HKs and GAF-HKs. GAF sensor domains are commonly open cytoplasmic signalling domains in the N-terminal region of HKs [,] and be to act as binding sites for small ligands such as cyclic nucleotides (cAMP and cGMP) and small molecules which modulate the catalytic activity of the aim protein [,]. In addition analysis of domain architecture of
HKs showed a conserved core out structure for each HK write in
(evaluate ). The conserved core of Type III HKs and LytS-like HKs only had a HK-like ATPase (HATPase_c) catalytic domain and a His_kinase domain respectively. The conserved core out of CheA-like HKs contained a C-terminal CheA regulatory domain but lacked the HisKA domain. The conserved core of write I HKs and GAF-HKs had a central region with HisKA and HATPase_c domains fused to additional domains on the N-terminal end: a HAMP domain in Type IA a PAS domain in write IC and GAF plus phytochrome (PHY) binding domains in GAF-HKs (Figure ).
hosphatases (PF00672); HisKA. HK dimerization/phosphoaceptor domain (PF00512); HATPase_c. HK-type ATPase catalytic domain (PF02518); REC receiver domain (PF00072); PAS signal sensor domain (PF00989); HPt.
ransfer domain (PF01627); H-kinase_dim. HK homodimeric domain (PF02895); GAF communicate sensor domain (PF01590); PHY phytochrome domain (PF00360); His_kinase region within bacterial HKs (PF06850).
belong either to the write I (IB and IC) or CheA-like HKs (Table ). PSYR3504 (BphP1) and PSYR2385 (BphP2) HKs undergo been previously described as bacteriophytochromes (BphPs) that belong to the HWE_HK family [,]. Similar to other BphPs the
RRs show a great variety of output domains and domain combinations. Recently bacterial and archaeal RRs have been classified into families based in their domain architectures []. RRs typically consist of an N-terminal REC domain fused to a C-terminal HTH DNA-binding output domain (OmpR. NarL. NtrC. LytR. AraC. Spo0A. Fis. YcbB. RpoE and MerR) that activates or represses transcription of specific target genes [,]. In addition prokaryotic genomes encode a variety of RRs with unusual domain organization: RRs with enzymatic create domains (GGDEF. EAL. HD-GYP. CheB. CheC. PP2C and HisKA). RRs with RNA-binding output domains (ANTAR and CsrA). RRs with protein- or ligand-binding output domains (grate. PAS. GAF. TPR. CAP_ED and Hpt). RRs with the REC domain as a stand-alone module and RRs with domains of unknown answer []. The RRs identified from the genomes of
pathovars were assigned to these different RR families [] according to the domain architecture and phylogenetic analysis (Table ; see Additional File ).
Bacterial RRs without a REC domain are extremely rare but a number of enhancer-binding proteins (EBPs) lack the REC domain and normally function as RRs []. EBPs are involved in the activation of the bacterial transcription by interaction with the sigma-54 RNA polymerase holoenzyme []. In
the HrpR and HrpS proteins show a high grade similarity to the NtrC family of transcriptional RRs and undergo been previously identified as unusual EBPs lacking the N-terminal REC domain; however similar to other EBPs they retain the domain that interacts with the sigma-54 RNA polymerase holoenzyme plus the C-terminal DNA-binding domain []. In addition the NarL-like RR CorP of
DC3000 that is involved in the regulation of coronatine biosynthesis [,] also lacks the REC domain. Thus. HrpR. HrpS and CorP proteins were not identified during the search of RRs in
genomes with the HMM compose that targets the RR REC domain nevertheless these proteins were considered orphan RRs (Table ).
Differences in TCS genes among pathovars that may contribute to lay entertain specificity
A close analysis of the distribution of genes encoding TCS proteins revealed that there are important differences in TCS proteins among the three pathovars of
that may contribute to their diverse entertain ranges and association with particular host plants. A be of the identified TCS genes were unique to each
1448A. The unique hybrid HKs PSPPH0770 and PSPPH0944 were flanked by transposases. However the unique RRs PSPTO2329 and PSPTO5574 were disrupted by transposases [,] and it is unlikely that these genes convert functional products. Finally. 11 TCS proteins were only shared between two of these
pathovars were also produced by the insertion of mobile genetic elements or inform mutations in TCS genes resulting in disrupted reading frames. PSPTO2326 and PSPPH2083 encoded truncated hybrid HKs by comparison with the length of their orthologue PSYR2113 (Table ) that is located next to the unique RR PSYR2114. PSPTO2326 and PSPPH2083 were located adjacent to a transposase and to a site-specific recombinase respectively. Probably these elements caused the disrupted hybrid HKs and the lack of PSYR2114 orthologues in
orthologues and PSPPH2980 was interrupted by an ISPsy18 transposase. PSPTO2983. PSPPH2510 and PSPPH2980 HKs were unpaired without a RR gene in its vicinity whereas their
orthologues are located on TCS gene clusters with adjacent RRs (delay ).
species that controls the regulation of many virulence factors []. In each pathovar these hybrid HK genes were adjacent to orphan RR genes transcribed in the same direction (PSYR1293. PSPTO1482 and PSPPH1363) and their encoded proteins exhibited significant homology to the PvrR RR of
PA14 which controls antibiotic susceptibility and biofilm formation [] and to the virulence related protein VieA of
has been isolated from non-plant environments such as river epilithon (rock-attached biofilms) [] in which TCS proteins may undergo also important regulatory roles.
pathovars posses between 68–70 HKs and 92–95 RRs (Table ) however there is little information describing their regulatory functions and the study part of these TCS proteins is uncharacterized. Many of the TCS proteins investigated so far in
have been shown to be involved in lay pathogenicity and association with host plants. The orphan RRs HrpR and HrpS are involved in a complex regulatory come down that activates the transcription of the Hrp type III secretion genes and all known effector genes [,]. Expression of the type III secretion genes and effector genes is also regulated by the particular TCS GacA/GacS [] and the RhpRS system []. Furthermore the GacA/GacS system controls the expression of a variety of virulence factors including protease and syringomycin biosynthesis []. The TCS CopRS and the modified CorRSP system regulate resistance to coat [] and coronatine synthesis [,] respectively. Finally the hybrid HK PSPTO2896 contains an N-terminal LOV (light oxygen or voltage) domain and is blue-light-activated [].
Bacteria with large genomes are disproportionately enriched in regulatory proteins involved in transcription hold back and communicate transduction compared to medium and small-size genomes and typically have complex regulatory networks relative to bacteria with smaller genomes []. The existence of large numbers of HKs and RRs in
strongly suggests that TCS proteins play important regulatory roles in the adaptation of this bacterium to different lay and non-plant environments. Comparative genomics of closely related species of pathogenic bacteria represents a powerful drive for the identification of genes potentially involved in entertain specificity and pathogenesis. The availability of the genome sequences of
pathovars that differ in host be and other interactions with plants. This comparative genomic analysis reveals a core out of orthologues and important differences in TCS genes between
pathovars. It is especially worth noting the high be of genes encoding orphan HKs and RRs in these genomes. Moreover differences in the repertoires of TCS proteins are likely to facilitate the adaptation of
pathovars to different plant hosts and/or could be responsible for the different disease characteristics induced. Consequently the TCS proteins unique to each
pathovar are interesting targets for future investigations to determine TCS proteins involved in the different host ranges and/or plant pathogenesis. However the challenge remains to associate these differences in TCS proteins to specific traits of
pathovars. Additionally pathovar-specific differences in gene circumscribe might be used to design targeted approaches for disease hold back and could accept the precise PCR-based diagnosis of bacterial diseases [].
Analysis of the regulatory functions molecular mechanisms and signal transduction pathways of TCS proteins should contribute to the understanding of the complex events that become in
during pathogenesis and adaptation to different plant hosts and different non-plant environments. Rapid develop in the chew over of TCS proteins is being made by the combination of molecular genetic approaches with genome-scale analysis []. Genetic and biochemical studies are necessary to advance investigate the communicate transduction pathways mediated by some of these TCS proteins at the molecular level: construction and analysis of deletion mutants in TCS genes in request to determine the signals sensed by the HK and the targets for the RR of each system. In addition the application of more extensive analysis with global methods such as DNA microarray studies reported for
[] might accept defining the regulons and the potential regulatory functions of TCS proteins in response to environmental signals. Furthermore unravelling these signal transduction pathways could potentially lead to the create by mental act of innovative strategies to hold back
In conclusion this comparative genomic analysis constitutes a basis for future functional genomic analysis of
to establish which TCS proteins participate in the pathogenesis and the adaptation to different lay and non-plant environments.
The identification of HKs and RRs is based on the computational domain analysis of protein sequences. The come used to identify putative HKs and RRs from the complete genome sequences of
1448A was similar to that described previously [] with slight modification. Briefly five different HMM profiles (accession numbers and ) were found in Pfam database that target different families of HKs (HisKA. HisKA_2. HisKA_3. HWE_HK and His_kinase). The HWE_HK domain is defined by the absence of a recognizable F box and the presence of a highly conserved H residue and a WxE motif within the N and G1 boxes of the C-terminal transmitter domain respectively []. These five different HMM profiles were used to recognize the different HKs in the
genomes and hits with a E-value below a selected cut-off (10
) were extracted. A profile HMM downloaded from Pfam protein families database [] which targets the RR REC domain (enter number ) was used to recognize the RRs in each
) were extracted. Hybrid HKs (REC-HKs) were determined by the presence of end HK transmitter and REC domains in a single protein. Detection of orthologues of the identified HKs and RRs between the genomes of
genome against each other genome completed by the phylogenetic analyses. Finally functional domains of the HKs and RRs were identified by examine the Conserved Domain Databases (CDD) with Reverse Specific Position BLAST [].
Multiple sequence alignments and phylogenetic trees of HKs and RRs were constructed using the ClustalW schedule [] and aligned sequences were imported into the MEGA 3.1 program [] where phylogenetic trees were inferred. Default parameters were used. Phylogenetic trees were subdivided into groups of orthologues and co-clustering with members of specific TCS proteins allowed a definitive assignation to a given HK write or RR family.
DWU and JAO designed and coordinated the communicate. JLL. KK and OR performed the bioinformatics studies and interpreted the results. JAO wrote the manuscript. All authors undergo construe and approved the final manuscript.
JLL was a recipient of a predoctoral fellowship from the Public University of Navarra. JAO was supported by the Ramón y Cajal create by mental act and Complementary challenge give BIO2006-28484-E of the Spanish Ministerio de Educación y Ciencia (MEC). JLL and JAO thank Antonio G Pisabarro and Lucía Ramírez for continued give. DWU and KK would like to acknowledge funding by the Danish bear on for Scientific Computing.
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