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''Pseudomonas syringae'' is a rod-shaped,
Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different
pathovar A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one o ...
s, all of which are available to researchers from international culture collections such as the NCPPB, ICMP, and others. ''Pseudomonas syringae'' is a member of the genus ''
Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...
'', and based on 16S rRNA analysis, it has been placed in the ''P. syringae'' group. It is named after the lilac tree (''
Syringa vulgaris ''Syringa vulgaris'', the lilac or common lilac, is a species of flowering plant in the olive family Oleaceae, native to the Balkan Peninsula, where it grows on rocky hills.Rushforth, K. (1999). ''Trees of Britain and Europe''. Collins .Med-Check ...
''), from which it was first isolated. A phylogenomic analysis of 494 complete genomes from the entire ''Pseudomonas'' genus showed that ''P. syringae'' does not form a monophyletic species in the strict sense, but a wider evolutionary group that also included other species as well, such as ''P. avellanae'', ''P. savastanoi'', ''P. amygdali'', and ''P. cerasi''. ''Pseudomonas syringae'' tests negative for arginine dihydrolase and oxidase activity, and forms the polymer levan on sucrose nutrient agar. Many, but not all, strains secrete the lipodepsinonapeptide plant toxin syringomycin, and it owes its yellow fluorescent appearance when cultured ''in vitro'' on King's B medium to production of the
siderophore Siderophores (Greek: "iron carrier") are small, high-affinity iron- chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is n ...
pyoverdin. ''Pseudomonas syringae'' also produces ice nucleation active (INA) proteins which cause water (in plants) to freeze at fairly high temperatures (), resulting in injury. Since the 1970s, ''P. syringae'' has been implicated as an atmospheric "biological ice nucleator", with airborne bacteria serving as cloud condensation nuclei. Recent evidence has suggested the species plays a larger role than previously thought in producing
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...
and
snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
. They have also been found in the cores of hailstones, aiding in bioprecipitation. These INA proteins are also used in making
artificial snow Snowmaking is the production of snow by forcing water and pressurized air through a "snow gun", also known as a "snow cannon". Snowmaking is mainly used at ski resorts to supplement natural snow. This allows ski resorts to improve the reliabilit ...
. ''Pseudomonas syringae'' pathogenesis is dependent on effector proteins secreted into the plant cell by the bacterial
type III secretion system The type III secretion system (T3SS or TTSS), also called the injectisome, is one of the bacterial secretion systems used by bacteria to secrete their effector proteins into the host's cells to promote virulence and colonisation. The T3SS is a ...
. Nearly 60 different type III effector families encoded by ''hop'' genes have been identified in ''P. syringae''. Type III effectors contribute to pathogenesis chiefly through their role in suppressing plant defense. Owing to early availability of the genome sequence for three ''P. syringae'' strains and the ability of selected strains to cause disease on well-characterized host plants, including '' Arabidopsis thaliana'', ''
Nicotiana benthamiana ''Nicotiana benthamiana'', colloquially known as benth or benthi, is a species of ''Nicotiana'' indigenous to Australia. It is a close relative of tobacco. A synonym for this species is ''Nicotiana suaveolens'' var. ''cordifolia'', a descrip ...
'', and the
tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
, ''P. syringae'' has come to represent an important model system for experimental characterization of the molecular dynamics of plant-pathogen interactions.


History

In 1961, Paul Hoppe of the
U.S. Department of Agriculture The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
studied a corn
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
by grinding up infected leaves each season, then applying the powder to test corn for the following season to track the disease. A surprise frost occurred that year, leaving peculiar results. Only plants infected with the diseased powder incurred frost damage, leaving healthy plants unfrozen. This phenomenon baffled scientists until graduate student Steven E. Lindow of the
University of Wisconsin–Madison A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United Stat ...
with D.C. Arny and C. Upper found a bacterium in the dried leaf powder in the early 1970s. Steven E. Lindow, now a plant pathologist at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
, found that when this particular bacterium was introduced to plants where it is originally absent, the plants became very vulnerable to frost damage. He went on to identify the bacterium as ''P. syringae'', investigate the role of ''P. syringae'' in ice nucleation and in 1977, discover the mutant ice-minus strain. He was later successful at producing the ice-minus strain of ''P. syringae'' through recombinant DNA technology, as well.


Genomics

Based on a comparative genomic and phylogenomic analysis of 494 complete genomes from the entire ''Pseudomonas'' genus, ''P. syringae'' does not form a monophyletic species in the strict sense, but a wider evolutionary group (34 genomes in total, organized into 3 subgroups) that includes other species as well. The core proteome of the ''P. syringae'' group comprised 2944 proteins, whereas the protein count and GC content of the strains of this group ranged between 4973 and 6026 (average: 5465) and between 58 and 59.3% (average: 58.6%), respectively.


Disease cycle

''Pseudomonas syringae'' overwinters on infected plant tissues such as regions of necrosis or
gummosis Gummosis is the formation of patches of a gummy substance on the surface of certain plants, particularly fruit trees. This occurs when sap oozes from wounds or cankers as a reaction to outside stimuli such as adverse weather conditions, infection ...
(sap oozing from wounds on the tree) but can also overwinter in healthy looking plant tissues. In the spring, water from rain or other sources will wash the bacteria onto leaves/blossoms where it will grow and survive throughout the summer. This is the epiphyte phase of ''P. syringae’s'' life cycle where it will multiply and spread but will not cause a disease. Once it enters the plant through a leaf's stomata or necrotic spots on either leaves or woody tissue then the disease will start. The pathogen will then exploit and grow in intercellular space causing the leaf spots and cankers. ''P. syringae'' can also survive in temperatures slightly below freezing. These below freezing temperatures increase the severity of infection within trees like sour cherry, apricot, and peach.


Epidemiology

Diseases caused by ''P. syringae'' tend to be favoured by wet, cool conditions—optimum temperatures for disease tend to be around , although this can vary according to the pathovar involved. The bacteria tend to be seed-borne, and are dispersed between plants by rain splash. Although it is a plant pathogen, it can also live as a
saprotroph Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...
in the phyllosphere when conditions are not favourable for disease. Some saprotrophic strains of ''P. syringae'' have been used as biocontrol agents against postharvest rots.


Mechanisms of pathogenicity

The mechanisms of ''P. syringae'' pathogenicity can be separated into several categories: ability to invade a plant, ability to overcome host resistance, biofilm formation, and production of proteins with ice-nucleating properties.


Ability to invade plants

Planktonic ''P. syringae'' is able to enter plants using its flagella and pili to swim towards a target host. It enters the plant via wounds of natural opening sites, as it is not able to breach the plant cell wall. An example of this is the partnership with the leaf-mining fly ''Scaptomyza flava'', which creates holes in leaves during oviposition that the pathogen can take advantage of. The role of
taxis A taxis (; ) is the movement of an organism in response to a stimulus such as light or the presence of food. Taxes are innate behavioural responses. A taxis differs from a tropism (turning response, often growth towards or away from a stim ...
in ''P. syringae'' has not been well-studied, but the bacteria are thought to use chemical signals released by the plant to find their host and cause infection.


Overcoming host resistance


Effectors

''Pseudomonas syringae'' isolates carry a range of
virulence factor Virulence factors (preferably known as pathogenicity factors or effectors in plant science) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following ...
s called type III secretion system (T3SS) effector proteins. These proteins primarily function to cause disease symptoms and manipulate the host's immune response to facilitate infection. The major family of T3SS effectors in ''P. syringae'' is the ''hrp'' gene cluster, coding for the Hrp secretion apparatus.


=Hop effectors

= HopZ1s are type III effectors which interfere with the ''
Glycine max Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...
'' 2-hydroxyisoflavanone dehydratase ('' GmHID1''). ''HopZ1b'' degrades
daidzein Daidzein (7-hydroxy-3-(4-hydroxyphenyl)-4H-chromen-4-one) is a naturally occurring compound found exclusively in soybeans and other legumes and structurally belongs to a class of compounds known as isoflavones. Daidzein and other isoflavones ar ...
after production, reducing concentrations and thus reducing the immunity it provides the plant.


Phytotoxins

The pathogens also produce phytotoxins which injure the plant and can suppress the host immune system. One such phytotoxin is
coronatine Coronatine (COR) is a toxin produced by the bacterium ''Pseudomonas syringae''. It is involved in causing stomata to re-open after they close in response to pathogen-associated molecular patterns, as well as interfering with the responses media ...
, found in pathovars ''Pto'' and ''Pgl''.


Elicitors

''Pst'' DC3000 produces a '' PsINF1'', the '' INF1'' in ''P. syringae''. Hosts respond with autophagy upon detection of this elicitor. Liu et al. 2005 finds this to be the only alternative to mass
hypersensitivity Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. They are usually referred to as an over-reaction of the immune ...
leading to mass
programmed cell death Programmed cell death (PCD; sometimes referred to as cellular suicide) is the death of a cell (biology), cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usually confers ...
.


Biofilm formation

''Pseudomonas syringae'' produces polysaccharides which allow it to adhere to the surface of plant cells. It also releases
quorum sensing In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...
molecules, which allows it to sense the presence of other bacterial cells nearby. If these molecules pass a threshold level, the bacteria change their pattern of gene expression to form a biofilm and begin expression of virulence-related genes. The bacteria secrete highly viscous compounds such as polysaccharides and DNA to create a protective environment in which to grow.


Ice-nucleating properties

''Pseudomonas syringae''—more than any mineral or other organism—is responsible for the surface frost damage in plants exposed to the environment. For plants without antifreeze proteins, frost damage usually occurs between as the water in plant tissue can remain in a supercooled liquid state. ''P. syringae'' can cause water to freeze at temperatures as high as , but strains causing ice nucleation at lower temperatures (down to ) are more common. The freezing causes injuries in the epithelia and makes the nutrients in the underlying plant tissues available to the bacteria. ''Pseudomonas syringae'' has ''ina'' (ice nucleation-active) genes that make INA proteins which translocate to the outer bacterial
membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
on the surface of the bacteria, where the proteins act as nuclei for ice formation. Artificial strains of ''P. syringae'' known as ice-minus bacteria have been created to reduce frost damage. ''Pseudomonas syringae'' has been found in the center of hailstones, suggesting the bacterium may play a role in Earth's hydrological cycle.


Management

Currently there is not a 100% effective way to eradicate ''P. syringae'' from a field. The most common way to control this pathogen is to spray bactericides with copper compounds or other heavy metals that can be combined with fungicides or other pest control chemicals. Chemical treatments with fixed copper such as
Bordeaux Bordeaux ( , ; Gascon oc, Bordèu ; eu, Bordele; it, Bordò; es, Burdeos) is a port city on the river Garonne in the Gironde department, Southwestern France. It is the capital of the Nouvelle-Aquitaine region, as well as the prefect ...
, copper hydroxide, and
cupric sulfate Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered hy ...
are used to stop the spread of ''P. syringae'' by killing the bacteria while it is in the epiphyte stage on leaves, or woody parts of trees - however resistant ''P. syringae'' strains do exist. Spraying antibiotics such as streptomycin and organic bactericides is another way to control ''P. syringae'' but is less common than the methods listed above.   New research has shown that adding ammonium (NH4+) nutrition to tomato plants can cause a metabolic change leading to resistance against ''Pseudomonas syringae.'' This "ammonium syndrome" causes nutrient imbalances in the plant and therefore triggers a defense response against the pathogen. Strict hygiene practices used in orchards along with pruning in early spring and summer were proven to make the trees more resistant to ''P. syringae.'' Cauterizing cankers found on orchard trees can save the tree's life by stopping the infection from spreading. Breeding plants for resistance is another somewhat effective way to avoid ''P. syringae.'' It has been successful in the cherry rootstock with ''Pseudomonas syringae'' pv. ''syringae'', but so far, no other species are 100% resistant to this pathogen. Resistance breeding is a slow process, especially in trees. Unfortunately, ''P. syringae'' bacteria can adapt genetically to infect resistant plants, and the process for resistance breeding has to start over again. A combination treatment of bacteriophage and carvacrol shows promise in control of both the
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
ic and
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
forms.


Pathovars

Following ribotype analysis, incorporation of several pathovars of ''P. syringae'' into other species was proposed (see '' P. amygdali'', '' 'P. tomato''', '' P. coronafaciens'', '' P. avellanae'', '' 'P. helianthi''', '' P. tremae'', '' P. cannabina'', and '' P. viridiflava''). According to this schema, the remaining pathovars are: * attacks maple '' Acer'' species. * attacks kiwifruit '' Actinidia deliciosa''. * attacks horse chestnut '' Aesculus hippocastanum'', causing bleeding canker. * attacks beets '' Beta vulgaris''. * attacks wheat '' Triticum aestivum''. * attacks the kohekohe tree ''
Dysoxylum spectabile Kohekohe ('' Dysoxylum spectabile'') is a medium-sized tree in the Meliaceae family, native to New Zealand. It is found in lowland and coastal forests throughout most of the North Island and also occurs in the Marlborough Sounds in the north ...
''. * attacks
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu a ...
''Glycine max'', causing bacterial blight of soybean. * attacks barley '' Hordeum vulgare''. * attacks wheat ''Triticum aestivum''. * attacks ''
Panicum ''Panicum'' (panicgrass) is a large genus of about 450 species of grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone. They are often large, annual or perennial grasses, growi ...
'' grass species. * attacks crabapple ''
Malus sylvestris ''Malus sylvestris'', the European crab apple, is a species of the genus ''Malus'', native to Europe. Its scientific name means "forest apple" and the truly wild tree has thorns. Description Wild apple has an expanded crown and often appears mo ...
'' species. * attacks nectarine and
peach The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy fruits with various characteristics, most called peaches and others (the glossy-skinned, non-f ...
. * causes halo blight of beans. * attacks peas ''
Pisum sativum The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
''. * attacks ''
Syringa ''Syringa'' is a genus of 12 currently recognized species of flowering woody plants in the olive family or Oleaceae called lilacs. These lilacs are native to woodland and scrub from southeastern Europe to eastern Asia, and widely and commonly ...
'', ''
Prunus ''Prunus'' is a genus of trees and shrubs, which includes (among many others) the fruits plums, Cherry, cherries, peaches, Peach#Nectarine, nectarines, apricots, and almonds. Native to the North American temperate regions, the neotropics of Sou ...
'', and '' Phaseolus'' species. * attacks
tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
. However, many of the strains for which new species groupings were proposed continue to be referred to in the scientific literature as pathovars of ''P. syringae'', including pathovars ''tomato'', ''phaseolicola'', and ''maculicola''. '' Pseudomonas savastanoi'' was once considered a pathovar or subspecies of ''P. syringae'', and in many places continues to be referred to as ''P. s.'' pv. ''savastanoi'', although as a result of DNA-relatedness studies, it has been instated as a new species. It has three host-specific pathovars: ''P. s.'' ''fraxini'' (which causes ash canker), ''P. s.'' ''nerii'' (which attacks oleander), and ''P. s.'' ''oleae'' (which causes olive knot).


Determinants of host specificity

A combination of the pathogen's effector genes and the plant's resistance genes is thought to determine which species a particular pathovar can infect. Plants can develop resistance to a pathovar by recognising
pathogen-associated molecular pattern Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals. A vast arra ...
s (PAMPs) and launching an immune response. These PAMPs are necessary for the microbe to function, so cannot be lost, but the pathogen may find ways to suppress this immune response, leading to an
evolutionary arms race In evolutionary biology, an evolutionary arms race is an ongoing struggle between competing sets of co-evolving genes, phenotypic and behavioral traits that develop escalating adaptations and counter-adaptations against each other, resembling an ...
between the pathogen and the host.


''Pseudomonas syringae'' as a model system

Owing to early availability of genome sequences for , ''P. syringae'' pv. ''syringae'' strain B728a, and ''P. syringae'' pv. ''phaseolicola'' strain 1448A, together with the ability of selected strains to cause disease on well-characterized host plants such as '' Arabidopsis thaliana'', ''
Nicotiana benthamiana ''Nicotiana benthamiana'', colloquially known as benth or benthi, is a species of ''Nicotiana'' indigenous to Australia. It is a close relative of tobacco. A synonym for this species is ''Nicotiana suaveolens'' var. ''cordifolia'', a descrip ...
'', and tomato, ''P. syringae'' has come to represent an important model system for experimental characterization of the molecular dynamics of plant-pathogen interactions. The ''P. syringae'' experimental system has been a source of pioneering evidence for the important role of pathogen gene products in suppressing plant defense. The nomenclature system developed for ''P. syringae'' effectors has been adopted by researchers characterizing effector repertoires in other bacteria, and methods used for bioinformatic effector identification have been adapted for other organisms. In addition, researchers working with ''P. syringae'' have played an integral role in the Plant-Associated Microbe Gene Ontology working group, aimed at developing gene ontology terms that capture biological processes occurring during the interactions between organisms, and using the terms for annotation of gene products.


''Pseudomonas syringae'' pv. ''tomato'' strain DC3000 and ''Arabidopsis thaliana''

As mentioned above, the genome of ''P. syringae'' pv. ''tomato'' DC3000 has been
sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...
, and approximately 40 Hop (Hrp Outer Protein) effectors - pathogenic proteins that attenuate the host cell - have been identified. These 40 effectors are not recognized by ''A. thaliana'' thus making ''P. syringae'' pv. ''tomato'' DC3000 virulent against it - that is, ''P. syringae'' pv. ''tomato'' DC3000 is able to infect ''A. thaliana'' - thus ''A. thaliana'' is
susceptible Susceptibility may refer to: Physics and engineering In physics the susceptibility is a quantification for the change of an extensive property under variation of an intensive property. The word may refer to: * In physics, the susceptibility of ...
to this pathogen. Many
gene-for-gene relationship The gene-for-gene relationship was discovered by Harold Henry Flor who was working with rust (''Melampsora lini'') of flax ('' Linum usitatissimum''). Flor showed that the inheritance of both resistance in the host and parasite ability to cause d ...
s have been identified using the two model organisms, ''P. syringae'' pv. ''tomato'' strain DC3000 and ''Arabidopsis''. The gene-for-gene relationship describes the recognition of pathogenic avirulence (''avr'') genes by host resistance genes (R-genes). ''P. syringae'' pv. ''tomato'' DC3000 is a useful tool for studying ''avr'': R-gene interactions in ''A. thaliana'' because it can be transformed with ''avr'' genes from other bacterial pathogens, and furthermore, because none of the endogenous ''hops'' genes is recognized by ''A. thaliana'', any observed ''avr'' recognition identified using this model can be attributed to recognition of the introduced ''avr'' by ''A. thaliana''. The transformation of ''P. syringae'' pv. ''tomato'' DC3000 with effectors from other pathogens have led to the identification of many R-genes in ''Arabidopsis'' to further advance knowledge of plant pathogen interactions. The '' Dynamin-related protein 2b/ drp2b'' gene in ''A. thaliana'' is not directly an immunity gene, but by helping move external material into the intracellular network is indirectly related, and some mutants increase susceptibility.


''Pseudomonas syringae'' pv. ''tomato'' strain DC3000, its derivatives, and its tomato host

As its name suggests, ''P. syringae'' pv. ''tomato'' DC3000 (''Pst'' DC3000) is virulent to tomato (''
Solanum lycopersicum The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish wor ...
''). However, the tomato cultivar Rio Grande-PtoR (RG-PtoR), harboring the resistance gene ''Pto'', recognizes key effectors secreted by ''Pst'' DC3000, making it resistant to the bacteria. Studying the interactions between the ''Pto''-expressing tomato lines and ''Pst'' DC3000 and its pathovars is a powerful system for understanding plant-microbe interactions. Like other plants, the tomato has a two-tier pathogen defense system. The first and more universal line of plant defense, pattern-triggered immunity (PTI), is activated when plant pattern recognition receptors (PRRs) on the cell surface bind to pathogen-associated molecular patterns (PAMPs). The other branch of plant immunity, effector-triggered immunity (ETI), is triggered when intracellular (Nucleotide-binding site, Leucine-rich repeat) NB-LRR proteins bind to an effector, a molecule specific to a particular pathogen. ETI is generally more severe than PTI, and when a threshold of defense activation is reached, it can trigger a hypersensitive response (HR), which is purposeful death of host tissue to prevent the spread of infection. Two key effectors secreted by ''Pst'' DC3000 are AvrPto and AvrPtoB, which initiate ETI by binding the Pto/Prf receptor complex in ''Pto''-expressing tomato lines like RG-PtoR. ''Pst'' DC3000 has been modified to create the mutant strain ''Pst'' DC3000''∆avrPto∆avrPtoB'' (''Pst'' DC3000∆∆), which expresses neither AvrPto nor AvrPtoB. By infecting RG-PtoR with ''Pst'' DC3000∆∆, ETI to the pathogen is not triggered due to the absence of the main effectors recognized by the Pto/Prf complex. In the lab this is highly valuable, as using ''Pst'' DC3000∆∆ allows researchers to study the function of PTI-candidate genes in RG-PtoR, which would otherwise be masked by ETI. Another useful DC3000 derivative is ''Pst'' DC3000''∆avrPto∆avrPtoB∆fliC'' (''Pst'' DC3000∆∆∆). Like ''Pst'' DC3000∆∆, this strain does not express AvrPto and AvrPtoB, but it also has an additional knock-out for ''fliC'', the gene encoding flagellin, whose fragments serve as main PAMPs required for tomato PTI. By comparing plants within the same line that have been infected with either ''Pst'' DC3000∆∆ or ''Pst'' DC3000∆∆∆, researchers can determine if genes of interest are important to the flagellin recognition pathway of PTI. By treating CRISPR-induced tomato knockout mutants (in a RG-PtoR background) with ''Pst'' DC3000, ''Pst'' DC3000''∆avrPto∆avrPtoB'', or ''Pst'' DC3000''∆avrPto∆avrPtoB∆fliC'' has led to the characterization of key components of the tomato immune system and continues to be used to further the field of tomato pathology.


Importance

''Pseudomonas syringae'' has impacted many crop and orchard industries with its various pathovars.


''P. s.'' pv. ''actinidiae''

Mesarich et al. 2017 provides several libraries for transposon insertion sequencing of mutants of ''P. s. a.'' The kiwifruit industry in New Zealand has suffered catastrophic losses since their first known outbreak in 2007 from ''P. syringae'' pv. ''actinidiae''. New Zealand is second to Italy in the total volume of kiwifruit exports making an annual revenue of $NZ 1 billion, making it the most economically valuable export in the country. In 2014 the loss of exports alone was as high as NZ$930 million. Growers had to pay for treatments, and removal of infected vines along with suffering the loss of capital value in their orchards. For some, the orchard values went from NZ$450,000/ha to $70,000/ha after the outbreak, which is the price of bare land. The total loss of equity for the country of New Zealand was as high as NZ$2 billion. Between 2010 and 2012 over of
Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
kiwi orchards either were killed by ''P. syringae'' pv. ''actinidiae'' or were killed to contain the disease. The financial consequences for growers and their suppliers were severe, as were the economic consequences more widely.


See also

*
Bioprecipitation Bioprecipitation is the concept of rain-making bacteria and was proposed by David Sands from Montana State University in 1982. The formation of ice in clouds is required for snow and most rainfall. Dust and soot particles can serve as ice nuclei, b ...
* Ice-minus bacteria * ''Pseudomonas'' phage Φ6 * National Collection of Plant Pathogenic Bacteria


References


External links

*
Type strain of ''Pseudomonas syringae'' at Bac''Dive'' – the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q311202 Pseudomonadales Bacterial plant pathogens and diseases Soybean diseases Bacteria described in 1904