PstDC3000
   HOME

TheInfoList



OR:

''Pseudomonas syringae'' is a rod-shaped,
Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...
bacterium Bacteria (; : 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 among the ...
with polar
flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
. As a
plant pathogen Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like orga ...
, 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 The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when com ...
, and others. ''Pseudomonas syringae'' is a member of the genus ''
Pseudomonas ''Pseudomonas'' is a genus of Gram-negative bacteria belonging to the family Pseudomonadaceae in the class Gammaproteobacteria. The 348 members of the genus demonstrate a great deal of metabolic diversity and consequently are able to colonize a ...
'', and based on
16S rRNA 16S ribosomal RNA (or 16Svedberg, S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as ...
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, it is widely cultivated for its scented flowers in Europe (particularly the north and west) and Nor ...
''), 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 In enzymology, an arginine deiminase () is an enzyme that catalyzes the chemical reaction :L-arginine + H2O \rightleftharpoons L-citrulline + NH3 Thus, the two substrates of this enzyme are L-arginine and H2O, whereas its two products are L- ...
and
oxidase In biochemistry, an oxidase is an oxidoreductase (any enzyme that catalyzes a redox reaction) that uses dioxygen (O2) as the electron acceptor. In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H2O) or hydrogen peroxid ...
activity, and forms the polymer levan on
sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...
nutrient
agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from " ogonori" and " tengusa". As found in nature, agar is a mixture of two components, t ...
. Many, but not all, strains secrete the lipodepsinonapeptide plant toxin
syringomycin Syringomycin E is a member of a class of lipodepsinonapeptide molecules that are secreted by the plant pathogen ''Pseudomonas syringae''. Lipodepsinonapeptides comprise a closed ring of nine nonribosomally synthesized amino acids bonded to a fatt ...
, 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 Pyoverdines (alternatively, and less commonly, spelled as pyoverdins) are fluorescent siderophores produced by certain pseudomonads. Pyoverdines are important virulence factors, and are required for pathogenesis in many biological models of infec ...
. ''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 Bioprecipitation is the concept of rain-making bacteria and was proposed by David Sands from Montana State University in the 1970s. This is precipitation that is beneficial for microbial and plant growth, it is a feedback cycle beginning with land ...
, with airborne bacteria serving as
cloud condensation nuclei Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2  μm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This c ...
. Recent evidence has suggested the species plays a larger role than previously thought in producing
rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...
and
snow Snow consists of 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 througho ...
. They have also been found in the cores of
hailstone Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
s, aiding in
bioprecipitation Bioprecipitation is the concept of rain-making bacteria and was proposed by David Sands from Montana State University in the 1970s. This is precipitation that is beneficial for microbial and plant growth, it is a feedback cycle beginning with lan ...
. 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) 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. While the type III secretion system has been ...
. 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 ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally ...
'', ''
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 descripti ...
'', and the
tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...
, ''P. syringae'' has come to represent an important model system for experimental characterization of the molecular dynamics of
plant-pathogen interaction Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organ ...
s.


History

In 1961, Paul Hoppe of the
U.S. Department of Agriculture The United States Department of Agriculture (USDA) is an executive department of the United States federal government that aims to meet the needs of commercial farming and livestock food production, promotes agricultural trade and production ...
studied a corn
fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
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 The University of Wisconsin–Madison (University of Wisconsin, Wisconsin, UW, UW–Madison, or simply Madison) is a public land-grant research university in Madison, Wisconsin, United States. It was founded in 1848 when Wisconsin achieved st ...
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 university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...
, 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 In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out of ...
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 Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...
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, infect ...
(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 In botany, a stoma (: stomata, from Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spa ...
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 In microbiology, the phyllosphere is the total above-ground surface of a plant when viewed as a habitat for microorganisms.Leveau, Johan H.J. (2006"Microbial communities in the phyllosphere" In: Riederer M. and Müller C. (Eds) ''Biology of the ...
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 Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathogen ...
, 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 A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
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 ''Scaptomyza flava'' is an herbivorous leaf mining fly species in the family Drosophilidae. In Latin, '' flava'' means golden or yellow. The fly is amber to dark brown in color and approximately 2.5 mm in length. In Europe and New Zealand t ...
'', which creates holes in leaves during
oviposition The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...
that the pathogen can take advantage of. The role of
taxis A taxis (; : taxes ) is the motility, movement of an organism in response to a Stimulus (physiology), stimulus such as light or the presence of food. Taxes are innate behavioural responses. A taxis differs from a tropism (turning response, often ...
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 botany) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following: * c ...
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

= s are type III effectors which interfere with the ''
Glycine max The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source of f ...
'' 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 a ...
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 mediat ...
, found in pathovars ''Pto'' and ''Pgl''.


Elicitors

''Pst'' DC3000 produces a ''
PsINF1 ''Pseudomonas syringae'' is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from internat ...
'', the '' INF1'' in ''P. syringae''. Hosts respond with
autophagy Autophagy (or autophagocytosis; from the Greek language, Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-depe ...
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) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes Imm ...
leading to mass
programmed cell death Programmed cell death (PCD) sometimes referred to as cell, or 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 usual ...
.


Biofilm formation

''Pseudomonas syringae'' produces
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
s which allow it to adhere to the surface of plant cells. It also releases
quorum sensing In biology, quorum sensing or quorum signaling (QS) is the process of cell-to-cell communication that allows bacteria to detect and respond to cell population density by gene regulation, typically as a means of acclimating to environmental disadv ...
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 Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival in temperatures below the freezing point of water. AFPs bind to small ...
, frost damage usually occurs between as the water in plant tissue can remain in a
supercooled Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. Per the established international definition, supercooling means ''‘cooling a substance be ...
liquid state. ''P. syringae'' can cause water to freeze at temperatures as high as , but strains causing ice
nucleation In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...
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 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 Ice-minus bacteria is a common name given to a variant of the common bacterium ''Pseudomonas syringae'' (''P. syringae''). This strain of ''P. syringae'' lacks the ability to produce a certain surface protein, usually found on wild-type ''P. syri ...
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
bactericide A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics. However, material surfaces can also have bactericidal properties based solely on their p ...
s 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 language, Gascon ; ) is a city on the river Garonne in the Gironde Departments of France, department, southwestern France. A port city, it is the capital of the Nouvelle-Aquitaine region, as well as the Prefectures in F ...
, copper hydroxide, and cupric sulfate 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 Streptomycin is an antibiotic medication used to treat a number of bacterial infections, including tuberculosis, Mycobacterium avium complex, ''Mycobacterium avium'' complex, endocarditis, brucellosis, Burkholderia infection, ''Burkholderia'' i ...
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 Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
(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 A bacteriophage (), also known informally as a phage (), is a virus that infects and replicates within bacteria. The term is derived . Bacteriophages are composed of proteins that Capsid, encapsulate a DNA or RNA genome, and may have structu ...
and
carvacrol Carvacrol, or cymophenol, C6H3(CH3)(OH)C3H7, is a monoterpene, monoterpenoid phenol. It has a characteristic pungent, warm odor of oregano. Natural occurrence Carvacrol is present in the essential oil of ''Origanum vulgare'' (oregano), oil of t ...
shows promise in control of both the
plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
ic and
biofilm A biofilm is a Syntrophy, syntrophic Microbial consortium, community of microorganisms in which cell (biology), cells cell adhesion, stick to each other and often also to a surface. These adherent cells become embedded within a slimy ext ...
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 Kiwifruit (often shortened to kiwi), or Chinese gooseberry, is the edible berry (botany), berry of several species of woody vines in the genus ''Actinidia''. The most common cultivar group of kiwifruit (Actinidia chinensis var. deliciosa, ...
''
Actinidia chinensis ''Actinidia chinensis'' is a fruiting vine native to China. It is one of some 40 related species of the genus '' Actinidia'', and the origin of most commercial varieties of kiwifruit. There are three accepted varieties of the species. ''Actini ...
''. * attacks horse chestnut ''
Aesculus hippocastanum ''Aesculus hippocastanum'', the horse chestnut, is a species of flowering plant in the maple, Sapindus, soapberry and lychee family Sapindaceae. It is a large, deciduous, synoecious (hermaphroditic-flowered) tree. It is also called horse-chestnu ...
'', causing bleeding canker. * attacks beets ''
Beta vulgaris ''Beta vulgaris'' (beet) is a species of flowering plant in the subfamily Betoideae of the family Amaranthaceae. Economically, it is the most important crop of the large order Caryophyllales. It has several cultivar groups: the sugar beet, of gre ...
''. * attacks wheat ''
Triticum aestivum Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield. Ta ...
''. * attacks the kohekohe tree '' Dysoxylum spectabile''. * 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. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...
''Glycine max'', causing bacterial blight of soybean. * attacks barley ''
Hordeum vulgare Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikelets ...
''. * attacks wheat ''Triticum aestivum''. * attacks ''
Panicum ''Panicum'' (panicgrass) is a large genus of about 250 species of Poaceae, grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone. They are often large, Annual plant, annual or P ...
'' grass species. * attacks crabapple ''
Malus sylvestris ''Malus sylvestris'', the European crab apple, also known as the European wild apple or simply the crab apple, is a species of the genus ''Malus''. Its scientific name means "forest apple", reflecting its habitat. It is native to western Eurasia ...
'' species. * attacks
nectarine The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in China. It bears edible juicy fruits with various characteristics, most called peaches and the glossy-skinned, non-fuzzy varieties called nectarines. Peach ...
and
peach The peach (''Prunus persica'') is a deciduous tree first domesticated and Agriculture, cultivated in China. It bears edible juicy fruits with various characteristics, most called peaches and the glossy-skinned, non-fuzzy varieties called necta ...
. * causes halo blight of beans. * attacks peas ''
Pisum sativum Pea (''pisum'' in Latin) is a pulse or fodder crop, but the word often refers to the seed or sometimes the pod of this flowering plant species. Peas are eaten as a vegetable. Carl Linnaeus gave the species the scientific name ''Pisum sativum ...
''. * attacks ''
Syringa ''Syringa'' is a genus of 12 currently recognized species of flowering plant, 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 wid ...
'', ''
Prunus ''Prunus'' is a genus of flowering plant, flowering trees and shrubs from the family (biology), family Rosaceae. The genus includes plums, cherries, peaches, nectarines, apricots and almonds (collectively Drupe, stonefruit). The genus has a cosm ...
'', and ''
Phaseolus ''Phaseolus'' (bean, wild bean) is a genus of herbaceous to woody annual and perennial vines in the family Fabaceae containing about 70 plant species, all native to the Americas, primarily Mesoamerica. It is one of the most economically importan ...
'' species. * attacks
tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...
. 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 ''Pseudomonas savastanoi'' is a gram-negative plant pathogenic bacterium that infects a variety of plants. It was once considered a pathovar of ''Pseudomonas syringae,'' but following DNA-relatedness studies, it was instated as a new species. It ...
'' 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 ''Nerium oleander'' ( ), commonly known as oleander or rosebay, is a shrub or small tree cultivated worldwide in temperate and subtropical areas as an ornamental and landscaping plant. It is the only species currently classified in the genus ...
), 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, but not present in the host. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both p ...
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 the ...
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 ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally ...
'', ''
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 descripti ...
'', 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 succi ...
, 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 Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its abilit ...
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 a ...
to this pathogen. Many
gene-for-gene relationship The gene-for-gene relationship is a concept in plant pathology that plants and their diseases each have single genes that interact with each other during an infection. It was proposed by Harold Henry Flor who was working with rust (''Melampsora l ...
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 (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originated from and was d ...
''). 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 Flagellins are a family of proteins present in flagellated bacteria which arrange themselves in a hollow cylinder to form the filament in a bacterial flagellum. Flagellin has a mass on average of about 40,000 daltons. Flagellins are the princi ...
, 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 CRISPR (; acronym of clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea. Each sequence within an individual prokaryotic CRISPR is d ...
-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
mutant In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It i ...
s 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, a Romance ethnic group related to or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance languag ...
kiwifruit 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 the 1970s. This is precipitation that is beneficial for microbial and plant growth, it is a feedback cycle beginning with lan ...
*
Ice-minus bacteria Ice-minus bacteria is a common name given to a variant of the common bacterium ''Pseudomonas syringae'' (''P. syringae''). This strain of ''P. syringae'' lacks the ability to produce a certain surface protein, usually found on wild-type ''P. syri ...
* ''Pseudomonas'' phage Φ6 *
National Collection of Plant Pathogenic Bacteria The National Collection of Plant Pathogenic Bacteria (NCPPB) is a bacterial culture repository hosted and maintained by Fera Science in York, United Kingdom. It specializes in bacterial plant pathogens and related bacteria. The NCPPB maintains ...


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