NORMAL GENOMIC

• Beattie GA
• Water relations in the interaction of foliar bacterial pathogens with plants.
• Annu Rev Phytopathol. 2011; 49: 533-55
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• This review examines the many ways in which water influences the relations between foliar bacterial pathogens and plants. As a limited resource in aerial plant tissues, water is subject to manipulation by both plants and pathogens. A model is emerging that suggests that plants actively promote localized desiccation at the infection site and thus restrict pathogen growth as one component of defense. Similarly, many foliar pathogens manipulate water relations as one component of pathogenesis. Nonvascular pathogens do this using effectors and other molecules to alter hormonal responses and enhance intercellular watersoaking, whereas vascular pathogens use many mechanisms to cause wilt. Because of water limitations on phyllosphere surfaces, bacterial colonists, including pathogens, benefit from the protective effects of cellular aggregation, synthesis of hygroscopic polymers, and uptake and production of osmoprotective compounds. Moreover, these bacteria employ tactics for scavenging and distributing water to overcome water-driven barriers to nutrient acquisition, movement, and signal exchange on plant surfaces.

• Klinkert B, Narberhaus F
• Microbial thermosensors.
• Cell Mol Life Sci. 2009; 66: 2661-76
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• Temperature is among the most important of the parameters that free-living microbes monitor. Microbial physiology needs to be readjusted in response to sudden temperature changes. When the ambient temperature rises or drops to potentially harmful levels, cells mount protective stress responses--so-called heat or cold shock responses, respectively. Pathogenic microorganisms often respond to a temperature of around 37 degrees C by inducing virulence gene expression. There are two main ways in which temperature can be measured. Often, the consequences of a sudden temperature shift are detected. Such indirect signals are known to be the accumulation of denatured proteins (heat shock) or stalled ribosomes (cold shock). However, this article focuses solely on direct thermosensors. Since the conformation of virtually every biomolecule is susceptible to temperature changes, primary sensors include DNA, RNA, proteins and lipids.

• Swiderski MR, Birker D, Jones JD
• The TIR domain of TIR-NB-LRR resistance proteins is a signaling domain involved in cell death induction.
• Mol Plant Microbe Interact. 2009; 22: 157-65
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• In plants, the TIR (toll interleukin 1 receptor) domain is found almost exclusively in nucleotide-binding (NB) leucine-rich repeat resistance proteins and their truncated homologs, and has been proposed to play a signaling role during resistance responses mediated by TIR containing R proteins. Transient expression in Nicotiana benthamiana leaves of "TIR + 80", the RPS4 truncation without the NB-ARC domain, leads to EDS1-, SGT1-, and HSP90-dependent cell death. Transgenic Arabidopsis plants expressing the RPS4 TIR+80 from either dexamethasone or estradiol-inducible promoters display inducer-dependent cell death. Cell death is also elicited by transient expression of similarly truncated constructs from two other R proteins, RPP1A and At4g19530, but is not elicited by similar constructs representing RPP2A and RPP2B proteins. Site-directed mutagenesis of the RPS4 TIR domain identified many loss-of-function mutations but also revealed several gain-of function substitutions. Lack of cell death induction by the E160A substitution suggests that amino acids outside of the TIR domain contribute to cell death signaling in addition to the TIR domain itself. This is consistent with previous observations that the TIR domain itself is insufficient to induce cell death upon transient expression.

• Sunderlikova V, Salaj J, Kopecky D, Salaj T, Wilhem E, Matusikova I
• Dehydrin genes and their expression in recalcitrant oak (Quercus robur) embryos.
• Plant Cell Rep. 2009; 28: 1011-21
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• In this work, three dehydrin genes, QrDhn1, QrDhn2, QrDhn3, were isolated from recalcitrant oak (Quercus robur). Their expression pattern was analyzed in both zygotic and somatic embryos as well as in vegetative tissues exposed to different kinds of abiotic stresses including desiccation, osmotic stress, and chilling. The QrDhn1 gene encoding for Y(n)SK(n) type dehydrin was expressed during later stages of zygotic embryo development but in somatic embryos only when exposed to osmotic or desiccation stress. In contrast, the other two oak dehydrin genes encoding for putative K(n) type dehydrins were expressed only in somatic embryos (both not-treated and osmotically stressed) and leaves of oak seedlings exposed to desiccation. Behavior of these genes suggests that different dehydrins are involved in processes of seed maturation and response to altered osmotic (water status) conditions in somatic embryos. Revealing further members of dehydrin gene family in recalcitrant oak might contribute to clarify non-orthodox seed behavior as well as identify mechanisms contributing to desiccation tolerance in plants.

• Gourion B, Francez-Charlot A, Vorholt JA
• PhyR is involved in the general stress response of Methylobacterium extorquens AM1.
• J Bacteriol. 2008; 190: 1027-35
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• PhyR represents a novel alphaproteobacterial family of response regulators having a structure consisting of two domains; a predicted amino-terminal extracytoplasmic function (ECF) sigma factor-like domain and a carboxy-terminal receiver domain. PhyR was first described in Methylobacterium extorquens AM1, in which it has been shown to be essential for plant colonization, probably due to its suggested involvement in the regulation of a number of stress proteins. Here we investigated the PhyR regulon using microarray technology. We found that the PhyR regulon is rather large and that most of the 246 targets are under positive control. Mapping of transcriptional start sites revealed candidate promoters for PhyR-mediated regulation. One of these promoters, an ECF-type promoter, was identified upstream of one-third of the target genes by in silico analysis. Among the PhyR targets are genes predicted to be involved in multiple stress responses, including katE, osmC, htrA, dnaK, gloA, dps, and uvrA. The induction of these genes is consistent with our phenotypic analyses which revealed that PhyR is involved in resistance to heat shock and desiccation, as well as oxidative, UV, ethanol, and osmotic stresses, in M. extorquens AM1. The finding that PhyR is involved in the general stress response was further substantiated by the finding that carbon starvation induces protection against heat shock and that this protection is at least in part dependent on PhyR.

• Stange C, Matus JT, Dominguez C, Perez-Acle T, Arce-Johnson P
• The N-homologue LRR domain adopts a folding which explains the TMV-Cg-induced HR-like response in sensitive tobacco plants.
• J Mol Graph Model. 2008; 26: 850-60
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• Following leaf infection with the tobacco mosaic virus (TMV), Nicotiana species that carry the disease resistance N gene develop a hypersensitive response (HR) that blocks the systemic movement of the virus. TMV-sensitive tobacco plants that lack the N gene develop classical disease symptoms following infection with most of the tobamoviruses. However, upon infection with TMV-Cg, these plants display a HR-like response that is unable to limit viral spread. We previously identified the NH gene in sensitive plants; this gene is homologous to the resistance N gene and both belong to the TIR/NBS/LRR family. Isolation and analysis of the NH transcript enabled the prediction of the amino acid sequence in which we detected a leucine-rich repeat domain, proposed to be involved in pathogen recognition. This domain is found in four of five classes of pathogen resistant proteins, in which sequence and structural changes may generate different specificities. In order to study the possible functional role of the LRR domain in the HR-like response, we developed a comparative three-dimensional model for the NH and N gene products, by means of functional and structural domains recognition, secondary structure prediction, domain assignment through profile Hidden Markov Models (HMM) and molecular dynamics (MD) simulations. Based on our results we postulate that the NH protein could adopt a LRR fold with a functional role in the HR-like response. Our two reliable LRR three-dimensional models (N-LRR, NH-LRR) can be used as structural frameworks for future experiments in which the structure-function relationships regarding the protein-protein interaction process may be revealed. Evolutionary aspects of the N and NH genes in Nicotiana species are also discussed.

• Zhou JM, Chai J
• Plant pathogenic bacterial type III effectors subdue host responses.
• Curr Opin Microbiol. 2008; 11: 179-85
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• Like animals, plants sense bacterial pathogens through surface-localized pattern recognition receptors (PRRs) and intracellular nucleotide-binding leucine-rich repeat proteins (NB-LRR) and trigger defense responses. Many plant-pathogenic bacteria secrete a large repertoire of effector proteins into host cells to modulate host responses, enabling successful infection and multiplication in plants. A number of these effector proteins target plant innate immunity signaling pathways, while others induce specific host genes to enhance plant susceptibility. Substantial progress has been made in the past two years concerning biochemical function of effectors and their host targets. These advances provide new insights into regulatory mechanisms of plant immunity and host-pathogen co-evolution.

• van Ooijen G, Mayr G, Kasiem MM, Albrecht M, Cornelissen BJ, Takken FL
• Structure-function analysis of the NB-ARC domain of plant disease resistance proteins.
• J Exp Bot. 2008; 59: 1383-97
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• Resistance (R) proteins in plants are involved in pathogen recognition and subsequent activation of innate immune responses. Most resistance proteins contain a central nucleotide-binding domain. This so-called NB-ARC domain consists of three subdomains: NB, ARC1, and ARC2. The NB-ARC domain is a functional ATPase domain, and its nucleotide-binding state is proposed to regulate activity of the R protein. A highly conserved methionine-histidine-aspartate (MHD) motif is present at the carboxy-terminus of ARC2. An extensive mutational analysis of the MHD motif in the R proteins I-2 and Mi-1 is reported. Several novel autoactivating mutations of the MHD invariant histidine and conserved aspartate were identified. The combination of MHD mutants with autoactivating hydrolysis mutants in the NB subdomain showed that the autoactivation phenotypes are not additive. This finding indicates an important regulatory role for the MHD motif in the control of R protein activity. To explain these observations, a three-dimensional model of the NB-ARC domain of I-2 was built, based on the APAF-1 template structure. The model was used to identify residues important for I-2 function. Substitution of the selected residues resulted in the expected distinct phenotypes. Based on the model, it is proposed that the MHD motif fulfils the same function as the sensor II motif found in AAA+ proteins (ATPases associated with diverse cellular activities)-co-ordination of the nucleotide and control of subdomain interactions. The presented 3D model provides a framework for the formulation of hypotheses on how mutations in the NB-ARC exert their effects.

• Zhang J, Wang X, Zhang Y, Zhang G, Wang J
• A conserved Hpa2 protein has lytic activity against the bacterial cell wall in phytopathogenic Xanthomonas oryzae.
• Appl Microbiol Biotechnol. 2008; 79: 605-16
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• The type III secretion system (TTSS) proteins form a needle-like structure injecting effector proteins into eukaryotic target cells. Although the TTSS forms an important pathway for bacterium-host interaction, its assembly process in vivo is poorly understood. The process is thought to include the opening of a pore before TTSS proteins are inserted into the bacterial cell wall. The proteins that break the bacterial cell wall have not yet been identified. We hypothesize that a hypersensitive response and pathogenicity (hrp) gene functions to digest the bacterial cell wall because it contains a conserved protein sequence similar to lytic transglycosylase. In this study, we cloned hrp-associated 2 (hpa2) genes from the bacteria Xanthomonas oryzae pathovars. We show in vitro that expressed Hpa2 protein has a lytic activity against bacterial cell walls. The analysis of a loss-of-function mutant of the hpa2 gene suggests that the hpa2 affects bacterial proliferation in host plants and a hypersensitive response in nonhost plants. As this is the first of such enzyme activity identified in the Hrp protein family, we speculate that the Hpa2 contributes to the assembly of the TTSS by enlarging gaps in the peptidoglycan meshwork of bacterial cell walls.

• Battaglia M, Olvera-Carrillo Y, Garciarrubio A, Campos F, Covarrubias AA
• The enigmatic LEA proteins and other hydrophilins.
• Plant Physiol. 2008; 148: 6-24

• Jia XY et al.
• Molecular cloning and characterization of wheat calreticulin (CRT) gene involved in drought-stressed responses.
• J Exp Bot. 2008; 59: 739-51
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• Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca(2+)-binding protein in multicellular eukaryotes. CRT plays a crucial role in many cellular processes including Ca(2+) storage and release, protein synthesis, and molecular chaperone activity. To elucidate the function of CRTs in plant responses against drought, a main abiotic stress limiting cereal crop production worldwide, a full-length cDNA encoding calreticulin protein namely TaCRT was isolated from wheat (Triticum aestivum L.). The deduced amino acid sequence of TaCRT shares high homology with other plant CRTs. Phylogenetic analysis indicates that TaCRT cDNA clone encodes a wheat CRT3 isoform. Southern analysis suggests that the wheat genome contains three copies of TaCRT. Subcellular locations of TaCRT were the cytoplasm and nucleus, evidenced by transient expression of GFP fused with TaCRT in onion epidermal cells. Enhanced accumulation of TaCRT transcript was observed in wheat seedlings in response to PEG-induced drought stress. To investigate further whether TaCRT is involved in the drought-stress response, transgenic plants were constructed. Compared to the wild-type and GFP-expressing plants, TaCRT-overexpressing tobacco (Nicotiana benthamiana) plants grew better and exhibited less wilt under the drought stress. Moreover, TaCRT-overexpressing plants exhibited enhanced drought resistance to water deficit, as shown by their capacity to maintain higher WUE (water use efficiency), WRA (water retention ability), RWC (relative water content), and lower MDR (membrane damaging ratio) (P < or = 0.01) under water-stress conditions. In conclusion, a cDNA clone encoding wheat CRT was successfully isolated and the results suggest that TaCRT is involved in the plant response to drought stress, indicating a potential in the transgenic improvements of plant water-stress.

• Zhou H et al.
• Molecular analysis of three new receptor-like kinase genes from hexaploid wheat and evidence for their participation in the wheat hypersensitive response to stripe rust fungus infection.
• Plant J. 2007; 52: 420-34
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• Considerable progress has been made in understanding the function of receptor-like kinase (RLK) genes in model plants. However, much less is known about these genes in crop species. Here we report the characterization of three new wheat RLK genes (TaRLK-R1, 2 and 3). The primary structure of the putative proteins TaRLK-R1, 2 and 3 contained a signal peptide, a cysteine-rich extracellular domain, a transmembrane domain, and a predicted intracellular kinase domain. The fusions between TaRLK-R1, 2 or 3 and the green fluorescence protein (GFP) were targeted to the plasma membrane; such targeting required the signal peptide, extracellular domain and transmembrane domain. Transcription of TaRLK-R1, 2 and 3 was found mainly in the green organs, and was regulated by light. Transcript levels of TaRLK-R1, 2 and 3 increased during the hypersensitive reaction (HR) to stripe rust fungus. In addition, the TaRLK-R3 transcript level was also upregulated by abiotic stresses. Further experiments revealed that the recombinant kinase domain of TaRLK-R3 exhibited auto-phosphorylation activity in vitro. Knocking down the transcript levels of TaRLK-R1, 2 or 3 individually or all together by virus-induced gene silencing compromised the wheat HR to stripe rust fungus. The demonstration of TaRLK-R1, 2 and 3 as positive contributors in the wheat HR to stripe rust fungus suggests a new direction for further functional studies of this important family of RLK genes, and may facilitate the breeding of wheat varieties resistant to stripe rust disease.

• Nimchuk ZL, Fisher EJ, Desveaux D, Chang JH, Dangl JL
• The HopX (AvrPphE) family of Pseudomonas syringae type III effectors require a catalytic triad and a novel N-terminal domain for function.
• Mol Plant Microbe Interact. 2007; 20: 346-57
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• Many gram-negative plant pathogenic bacteria employ type III secretion systems to deliver effector proteins directly into the host cell during infection. On susceptible hosts, type III effectors aid pathogen growth by manipulating host defense pathways. On resistant hosts, some effectors can activate specific host disease resistance (R) genes, leading to generation of rapid and effective immune responses. The biochemical basis of these processes is poorly understood. The HopX (AvrPphE) family is a widespread type III effector among phytopathogenic bacteria. We determined that HopX family members are modular proteins composed of a conserved putative cysteine-based catalytic triad and a conserved potential target/cofactor interaction domain. HopX is soluble in host cells. Putative catalytic triad residues are required for avirulence activity on resistant bean hosts and for the generation of a cell-death response in specific Arabidopsis genotypes. The putative target/cofactor interaction domain is also required for these activities. Our data suggest that specific interaction with and modification of a cytosolic host target drives HopX recognition in resistant hosts and may contribute to virulence in susceptible hosts. Surprisingly, the Legionella pneumophila genome was found to contain a protein with similarity to HopX in sequence and domain arrangement, suggesting that these proteins might also contribute to animal pathogenesis and could be delivered to plant and animal hosts by diverse secretion systems.

• Zhang D, Martyniuk CJ, Trudeau VL
• SANTA domain: a novel conserved protein module in Eukaryota with potential involvement in chromatin regulation.
• Bioinformatics. 2006; 22: 2459-62
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• Since packaging of DNA in the chromatin structure restricts the accessibility for regulatory factors, chromatin remodeling is required to facilitate nuclear processes such as gene transcription, replication, and genome recombination. Many conserved non-enzymatic protein domains have been identified that contribute to the activities of multiprotein remodeling complexes. Here we identified a novel conserved protein domain in Eukaryota whose putative function may be in regulating chromatin remodeling. Since this domain is associated with a known SANT domain in several vertebrate proteins, we named it the SANTA (SANT Associated) domain. Sequence analysis showed that the SANTA domain is approximately a 90 amino acid module and likely composed of four central beta-sheets and three flanking alpha-helices. Many hydrophobic residues exhibited high conservation along the domain, implying a possible function in protein-protein interactions. The SANTA domain was identified in mammals, chicken, frog, fish, sea squirt, sea urchin, worms and plants. Furthermore, a phylogenetic tree of SANTA domains showed that one plant-specific duplication event happened in the Viridiplantae lineage.

• Jacques A, Ghannam A, Erhardt M, de Ruffray P, Baillieul F, Kauffmann S
• NtLRP1, a tobacco leucine-rich repeat gene with a possible role as a modulator of the hypersensitive response.
• Mol Plant Microbe Interact. 2006; 19: 747-57
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• Plant defense responses against pathogens often involve the restriction of the pathogen to its site of penetration achieved through the combined effects of the hypersensitive response (HR) and its tightly connected localized acquired resistance (LAR). The tobacco DD9-3 expressed sequence tag was previously isolated from a screen designed to isolate genes induced early during the HR, thus potentially involved in the induction/regulation of the HR or LAR. Translation of the open reading frame of DD9-3 revealed a leucine-rich repeat (LRR) domain highly homologous with the receptor domain of a receptor kinase, suggesting a potential function in signaling pathways. The full-length cDNA was cloned. It encodes a small (232 amino acids) LRR protein, designated Nicotiana tabacum leucine-rich protein 1 (NtLRP1), containing a signal peptide, four leucine zipper repeats, five LRR repeats, and a C-terminal domain rich in proline. NtLRP1 expression is induced early during the HR initiated by elicitins, Ralstonia solanacearum, or Tobacco mosaic virus. NtLRP1 coupled with the green fluorescent protein localizes to the endoplasmic reticulum (ER). Loss-of-function through virus-induced gene silencing or through RNA interference did not modify the elicitin-induced HR or LAR. Gain-of-function experiments through transient Agrobacterium tumefaciens-mediated NtLRP1 expression in tobacco leaves caused the suppression of the HR induced by 2 nM elicitin and delayed the HR when the elicitin was applied at higher concentrations. The results suggest that NtLRP1 acts as a modulator of the HR and that retention in the ER is essential for its function.

• Meng X, Bonasera JM, Kim JF, Nissinen RM, Beer SV
• Apple proteins that interact with DspA/E, a pathogenicity effector of Erwinia amylovora, the fire blight pathogen.
• Mol Plant Microbe Interact. 2006; 19: 53-61
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• The disease-specific (dsp) gene dspA/E of Erwinia amylovora encodes an essential pathogenicity effector of 198 kDa, which is critical to the development of the devastating plant disease fire blight. A yeast two-hybrid assay and in vitro protein pull-down assay demonstrated that DspA/E interacts physically and specifically with four similar putative leucine-rich repeat (LRR) receptor-like serine/threonine kinases (RLK) from apple, an important host of E. amylovora. The genes encoding these four DspA/E-interacting proteins of Malus xdomestica (DIPM1 to 4) are conserved in all genera of hosts of E. amylovora tested. They also are conserved in all cultivars of apple tested that range in susceptibility to fire blight from highly susceptible to highly resistant. The four DIPMs have been characterized, and they are expressed constitutively in host plants. In silico analysis indicated that the DIPMs have similar sequence structure and resemble LRR RLKs from other organisms. Evidence is presented for direct physical interaction between DspA/E and the apple proteins encoded by the four identified clones, which may act as susceptibility factors and be essential to disease development. Knowledge of DIPMs and the interaction with DspA/E thus may facilitate understanding of fire blight development and lead to new approaches to control of disease.

• Tang X, Xiao Y, Zhou JM
• Regulation of the type III secretion system in phytopathogenic bacteria.
• Mol Plant Microbe Interact. 2006; 19: 1159-66
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• The type III secretion system (TTSS) is a specialized protein secretion machinery used by numerous gram-negative bacterial pathogens of animals and plants to deliver effector proteins directly into the host cells. In plant-pathogenic bacteria, genes encoding the TTSS were discovered as hypersensitive response and pathogenicity (hrp) genes, because mutation of these genes typically disrupts the bacterial ability to cause diseases on host plants and to elicit hypersensitive response on nonhost plants. The hrp genes and the type III effector genes (collectively called TTSS genes hereafter) are repressed in nutrient-rich media but induced when bacteria are infiltrated into plants or incubated in nutrient-deficient inducing media. Multiple regulatory components have been identified in the plant-pathogenic bacteria regulating TTSS genes under various conditions. In Ralstonia solanacearum, several signal transduction components essential for the induction of TTSS genes in plants are dispensable for the induction in inducing medium. In addition to the inducing signals, recent studies indicated the presence of negative signals in the plant regulating the Pseudomonas syringae TTSS genes. Thus, the levels of TTSS gene expression in plants likely are determined by the interactions of multiple signal transduction pathways. Studies of the hrp regulons indicated that TTSS genes are coordinately regulated with a number of non-TTSS genes.

• Mukherjee K, Burglin TR
• MEKHLA, a novel domain with similarity to PAS domains, is fused to plant homeodomain-leucine zipper III proteins.
• Plant Physiol. 2006; 140: 1142-50
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• Homeodomain (HD) proteins play important roles in the development of plants, fungi, and animals. Here we identify a novel domain, MEKHLA, in the C terminus of HD-Leu zipper (HD-ZIP) III plant HD proteins that shares similarity with a group of bacterial proteins and a protein from the green alga Chlamydomonas reinhardtii. The group of bacterial MEKHLA proteins is found in cyanobacteria and other bacteria often found associated with plants. Phylogenetic analysis suggests that a MEKHLA protein transferred, possibly from a cyanobacterium or an early chloroplast, into the nuclear genome of an early plant in a first step, and attached itself to the C terminus of an HD-ZIP IV homeobox gene in a second step. Further position-specific iterated-BLAST searches with the bacterial MEKHLA proteins revealed a subregion within the MEKHLA domain that shares significant similarity with the PAS domain. The PAS domain is a sensory module found in many proteins through all kingdoms of life. It is involved in light, oxygen, and redox potential sensation. The fact that HD-ZIP III proteins are transcription factors that have this sensory domain attached to their C terminus uncovers a potential new signaling pathway in plants.

• Howles P et al.
• Autoactive alleles of the flax L6 rust resistance gene induce non-race-specific rust resistance associated with the hypersensitive response.
• Mol Plant Microbe Interact. 2005; 18: 570-82
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• L6 is a nucleotide binding site-leucine rich repeat (NBS-LRR) gene that confers race-specific resistance in flax (Linum usitatissimum) to strains of flax rust (Melampsora lini) that carry avirulence alleles of the AvrL567 gene but not to rust strains that carry only the virulence allele. Several mutant and recombinant forms of L6 were made that altered either the methionine-histidine-aspartate (MHD) motif conserved in the NBS domain of resistance proteins or exchanged the short domain C-terminal to the LRR region that is highly variable among L allele products. In transgenic flax some of these alleles are autoactive; they cause a gene dosage-dependent dwarf phenotype and constitutive expression of genes that are markers for the plant defense response. Their effects and penetrance ranged from extreme to mild in their degree of plant stunting, survival, and reproduction. Dwarf plants were also resistant to flax rust strains virulent to wild-type L6 plants, and this nonspecific resistance was associated with a hypersensitive response (HR) at the site of rust infection. The strongest autoactive allele, expressed in Arabidopsis from an ethanol-inducible promoter, gave rise to plant death dependent on the enhanced disease susceptibility 1 (EDS1) gene, which indicates that the mutant flax (Linaceae) L6 gene can signal cell death through a defined disease-resistance pathway in a different plant family (Brassicaceae).

• Ciccarelli FD, Bork P
• The WHy domain mediates the response to desiccation in plants and bacteria.
• Bioinformatics. 2005; 21: 1304-7
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• MOTIVATION: The hypersensitive response (HR) is a process activated by plants after microbial infection. Its main phenotypic effects are both a programmed death of the plant cells near the infection site and a reduction of the microbial proliferation. Although many resistance genes (R genes) associated to HR have been identified, very little is known about the molecular mechanisms activated after their expression. RESULTS: The analysis of the product of one of the R genes, the Hin1 protein, led to the identification of a novel domain, which we named WHy because it is detectable in proteins involved in Water stress and Hypersensitive response. The expression of this domain during both biotic infection and response to desiccation points to a molecular machinery common to these two stress conditions. Moreover, its presence in a restricted number of bacteria suggests a possible use for marking plant pathogenicity. CONTACT: francesca.ciccarelli@embl.de SUPPLEMENTARY INFORMATION: Supplementary data (Figures S1 and S2 and Table S1) and the alignment in clustal format are available at http://www.bork.embl.de/~ciccarel/WHy_add_data.html.

• Wittenberg JB, Bolognesi M, Wittenberg BA, Guertin M
• Truncated hemoglobins: a new family of hemoglobins widely distributed in bacteria, unicellular eukaryotes, and plants.
• J Biol Chem. 2002; 277: 871-4

• Prade RA, Zhan D, Ayoubi P, Mort AJ
• Pectins, pectinases and plant-microbe interactions.
• Biotechnol Genet Eng Rev. 1999; 16: 361-91

• Collmer A
• Determinants of pathogenicity and avirulence in plant pathogenic bacteria.
• Curr Opin Plant Biol. 1998; 1: 329-35
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• Many plant pathogenic bacteria possess a conserved protein secretion system that is thought to transfer Avr (avirulence) proteins, with potential activities in both parasitism and defense elicitation, into plant cells. avr genes may be acquired horizontally by these bacteria, and avr gene compositions are highly variable. In the past year, heterologous expression experiments have revealed that the products of avr genes can be interchanged among different genera of bacteria with retention of secretion, pathogenicity, and avirulence activities, suggesting mechanisms for rapid coevolution of these parasites with changing plant hosts.

• Osbourn AE, Bowyer P, Daniels MJ
• Saponin detoxification by plant pathogenic fungi.
• Adv Exp Med Biol. 1996; 404: 547-55

• Dure L 3rd
• A repeating 11-mer amino acid motif and plant desiccation.
• Plant J. 1993; 3: 363-9
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• Among the proteins that accumulate as plant seeds desiccate are several protein families that are composed principally of a tandemly repeated 11-mer amino acid motif. Proteins containing the same motif accumulate in the desiccating leaves of a desiccation-tolerant plant species. This motif is characterized by apolar residues in positions 1, 2, 5 and 9, and charged or amide residues in positions 3, 6, 7, 8 and 11. An alpha helical arrangement of the 11-mer repeating unit gives an amphiphilic helix whose hydrophobic stripe twists in a right-handed fashion around the helix. Should these proteins dimerize via binding of their hydrophobic faces, a right-handed coiled coil would be formed. Such a structure has not previously been observed. A conceivable function for these proteins in ion sequestration in the desiccated state is proposed.

• Close TJ, Lammers PJ
• An osmotic stress protein of cyanobacteria is immunologically related to plant dehydrins.
• Plant Physiol. 1993; 101: 773-9
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• Dehydrins are a family of desiccation proteins that were identified originally in plants (T.J. Close, A.A. Kortt, P.M. Chandler [1989] Plant Mol Biol 13: 95-108; G. Galau, T.J. Close [1992] Plant Physiol 98: 1523-1525). Dehydrins are characterized by the consensus amino acid sequence domain EKKGIMDKIKEKLPG found at or near the carboxy terminus; the core of this domain (KIKEKLPG) may be repeated from one to many times within the complete polypeptide. Dehydrins generally accumulate in plants in response to dehydration stress, regardless of whether the stimulus is evaporation, chilling, or a decrease in external osmotic potential. Polyclonal antibodies highly specific to the consensus carboxy terminus of plant dehydrins were used to search for dehydrins in cyanobacteria, many of which are known to survive desiccation. A 40-kD osmotic-stress-induced protein was identified in Anabaena sp. strain PCC 7120. The 40-kD protein was usually not detected in logarithmic cultures and was induced by shifting the growth medium to higher solute concentrations. Several solutes have inductive effects, including sucrose, sorbitol, and polyethylene glycol (PEG). Measurements of osmotic potential suggest that a shift of -0.5 MPa (sucrose and PEG) or -1.2 MPa (sorbitol) is sufficient to induce synthesis of the 40-kD protein. Glycerol, which is highly permeable, was not an inducer at -1.2 MPa (0.5 M), nor was the plant hormone abscisic acid. Induction appears to be evoked by a shift in osmotic potential approximately equal in absolute magnitude to the expected turgor pressure of bacterial cells in logarithmic phase growth. A dehydrin-like polypeptide was also identified among osmotically induced proteins from two other filamentous, heterocyst-forming cyano-bacteria. A 40-kD protein was observed in Calothrix sp. strain PCC 7601, and in Nostoc sp. strain Mac-R2, an osmotic-induced doublet at 39 and 40 kD was observed. From these data, it appears that cyanobacteria produce a dehydrin-like protein under osmotic stress.

• Prasad M
• The dynamics of amino acid variations during pathogenesis and host resistance.
• Zentralbl Bakteriol Naturwiss. 1980; 135: 162-84

• Iurchak LD
• [Biological activity of microorganism metabolites decomposing the lupine green mass].
• Mikrobiol Zh. 1971; 33: 730-1

• FASQUELLER R, BARBIER P
• [A few examples on preservation of bacterial and virus viability by desiccation under congelation].
• C R Seances Soc Biol Fil. 1950; 144: 1618-21

• Hammer BW
• A Note on the Vacuum Desiccation of Bacteria.
• J Med Res. 1911; 24: 527-30