Pr protein

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Assignment on

PATHOGENESIS RELATED PROTEINS

Submitted byPrathmesh G. JoshiM.Sc (Agri) Biochemistry,AAU,Anand.

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Content

Introduction

Occurrence of PR protein

Properties of PR protein

Induction of PR protein

Families of PR protein

Function of PR protein

Conclusion

Recent studies

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INTRODUCTION

Pathogenesis-related proteins, often called PR proteins, are a structurally diverse

group of plant proteins that are toxic to invading fungal pathogens.

They are widely distributed in plants in trace amounts, but are produced in much

greater concentration in pathogen attack or stress.

Varying types of PR proteins have been isolated from each of several crop plants.

Different plant organs, e.g., leaves, seeds, and roots, may produce different sets of PR

proteins.

The several groups of PR proteins have been classified according to their function,

serological relationship, amino acid sequence, molecular weight, and certain other

properties.

PR proteins are either extremely acidic or extremely basic and therefore are highly

soluble and reactive.

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At least 14 families of PR proteins are recognized. The better known PR proteins are

PR1 proteins (antioomycete and antifungal),

PR2 (b-1,3-glucanases),

PR3 (chitinases),

PR4 proteins (antifungal),

PR6 (proteinase inhibitors)

thaumatine-like proteins,

Defensins, thionins, lysozymes, osmotinlike proteins, lipoxygenases, cysteine-rich

proteins, glycine-rich proteins, proteinases, chitosanases, and peroxidases.

There are often numerous isoforms of each PR protein in various host plants.

Although healthy plants may contain trace amounts of several PR proteins, attack by

pathogens, treatment with elicitors, wounding, or stress induce transcription of a

battery of genes that code for PR proteins .

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Occurrence:-

1. In several plant species upon infection with viruses, viroids or bacteria the

development of symptoms is accompanied by appearance of one or more new

proteins. such protein found in tobacco & recently has been detected in 16 species.

3. The occurance of these new proteins is not pathogen specific but determined by the

type of reaction in host plant this is indicated that they are host specific.

4. All are identified by polyacrylamide gel electrophoresis run either in the absence or in

the presence of SDS & stained with general protein stains.

5. At least tobacco & cowpea ,PRs are found predominantly outside the cytoplasm in the

intercellular spaces.

6. They must secreted through plasma lemma.at least four tobacco PRs first identified

are not glycoproteins nor oxidase or hydrolases such as peroxidases, Ribonuclease,

protease & phosphatase which are known to be present in intercellular space.

7. Their resistance to proteases in an obvious requirement for a function in this

environment in which proteolytic enzyme abound.

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Properties:-

1.Both tobacco & bean PR elute from gel filtration columns than bulk of protein from

healthy leaves i.e it indicate that they are low molecular weight protein & their large

polyacrylamide gel electrophoresis due to charge differences.

2. They are selectively low pH, where they are soluble than other proteins. Ten PRs can be

identified as prominent bands when crude low pH extracts are subjected to the same

electrophoretic procedure.

3.They are highly resistant to the endogenous plant proteases as well as to commercial

protease preparation including trypsin.chymotrypsin,papain, & protease k.

4.They are not protease inhibitor nor produced by treatment of protein extracts from non

infected leaves with proteases.

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Induction of PR protein :-

1.They are induced by plasmolysis. since they are also induced artificially by the

application of a variety of chemicals notably Polyacrylic acid, Benzoic acid derivatives .

2. Various plant hormones as well as culture filtrates from pathogenic fungus or

bacterium. It has been proposed that induction might be the result of some type of

stress.

3. Ethylene is produced by most plant tissues as a general reaction to stress & PRs can

be induced in all tobacco tested to date by ethepon by which ethylene released in plant

as well as natural precursor of ethylene i.e 1-aminocyclopropane-1-carboxylic acid

(ACC).

4. This gives idea that the induction of PRs is mediated by ethylene, at least in tobacco .

5.Induction under all conditions investigated so far is associated with stimulated

ethylene production.

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6. When leaf discs infected with TMV were floated on a solution of amino

ethoxyvinylglycine which specially blocks the formation of ACC

(1-aminocyclopropane-1-carboxylic acid) in biosynthesis of ethylene.

7.Induction of PRs by ethepon or salicylic acid in tobacco is inhibited by cyclohexamide

or D-2-(4-methyl-2,6-dinitroanilin)-N-methyl propionamide both inhibitor of protein

synthesis on cytoplasmic ribosomes.

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Sr No. Family Type /Member Properties

1. PR-1 Tobacco PR-1a Unknown

2. PR-2 Tobacco PR-2 β-1,3-glucanase

3. PR-3 Tobacco P,Q Chitinase type I,II,IV,V,VI,VII

4. PR-4 Tobacco R Chitinase type I,II

5. PR-5 Tobacco S Thaumatin like protein

6. PR-6 Tomato Inhibitor-I Protease inhibitor

7. PR-7 Tomato P69 Endoproteinase

8. PR-8 Cucumber chitinase Chitinase type III

9. PR-9 Tobacco lignin forming peroxidase

Peroxidase

10. PR-10 Parsley PR-1 Ribosome inactivating protein

11. PR-11 Tobacco class V chitinase Chitinase type I

12. PR-12 Radish R5 AFP-3 Defensins

13. PR-13 Arabidopsis TH.12-1 Thionins

14. PR-14 Barley LTP-4 Lipid transfer protein

The families of pathogenesis-related proteins

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Pathogenesis-related (PR) protein 1

The first PR- 1 protein was discovered in 1970.

Since then, a number of PR-1 proteins have been identified in

1. Arabidopsis

2. Barley

3. Tobacco

4. Rice

5. Pepper

6. Tomato

7. Wheat

8. Maize

These PR-1 having 14 to 17 kD molecular weight and mostly of basic nature.

Occurance & Molecular nature

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Non-expressors of Pathogenesis-Related Genes1 (NPR1) regulate systemic acquired

resistance via regulation pathogenesis related-1 (PR-1) in Arabidopsis thaliana.

The interaction of nucleus-localized NPR1 with TGA transcription factors, after reduction

of cysteine residues of NPR 1 by salicylic acid (SA) results in the activation of defense

genes of PR-1. In the absence of TAG 2 and/or SA expression of PR-1 not occur in

Arabidopsis thaliana.

PR-1 proteins have antifungal activity at the micromolar level against a number of plant

pathogenic fungi, including Uromyces fabae, Phytophthora infestans, and Erysiphe

graminis.

The exact mode of action of the antifungal activities of these proteins are yet to

be identified but a PR-1-like protein, helothermine, from the Mexican banded

lizard have been found to be interacting with the membrane-channel proteins of

target cells, inhibiting the release of Ca2+.

Mode of action

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Pathogenesis related protein-2

Example:- β-Glucanases

Occurance & Properties:-

Plant β-1,3-glucanases ( β -1,3-Gs) comprises of large and highly complex gene families

involved in pathogen defense as well as a wide range of normal developmental processes.

β -1,3-Gs have molecular mass in the range from 33 to 44 kDa .

These enzymes are found in wide variety of plants like

1. Peanut,

2. Chickpea

3. Tobacco, etc. and having resistivity against various fungi like Aspergillus parasiticus, A.

flavs, Blumeria graminis.

These enzymes have wide range of isoelectric pH.

Most of the basic -1,3-Gs are localized in vacuoles of the plant cells while the acidic β β –

1,3-Gs are secreted outside the plant cell.

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Wounding, hormonal signals like methyl jasmonate and ethylene , pathogen attack like

fungus Colletotrichum lagenarium and some fungal elicitors releases from pathogen

cell wall can also induced -1,3-Gs in the various parts of plant.β

-1,3-glucanases are involves in β hydrolytic cleavage of the 1,3-β-D-glucosidic linkages

in -1,3-glucans, a major componant of fungi cell wall. So that β cell lysis and cell death

occur as a result of hydrolysis of glucans present in the cell wall of fungi.

The enzyme -1,3-Gs was found to be strongly induced by ultraviolet (UV-B; 280– β

320nm) radiation in primary leaves of French bean (Phaseolus vulgaris), so that UV-I

induced DNA damage is a primary step for the induction of -1,3-Gs.β

-1,3- glucanases β and chitinases are down regulated by combination of auxin and

cytokinin while Abscisic acid (ABA) at a concentration of 10 M markedly inhibited the μ

induction of -1,3-glucanases but not of chitinases.β

Mode of Action

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Occurrence & properties

Example:- Chitinase

Most of Chitinase having molecular mass in the range of 15 kDa and 43 kDa.

Chitinase can be isolated from Chickpea, Cucumber, barley.

The main substrate of Chitinases is chitin is a natural homopolymer of -1,4- linkedβ N-

acetylglucosamine residues.

Chitinases can be divided into two categories:

1. Exochitinases:- demonstrating activity only for the non-reducing end of the chitin chain.

2. Endochitinases:- which hydrolyse internal -1,4- glycoside bonds.β

Many plant endochitinases,especially those with a high isoelectric point, exhibit an

additional lysozyme or lysozyme like activity.

Chitinase and -1,3-Glucanase are differentially regulated by Wounding, Methyl β

Jasmonate, Ethylene, and Gibberellin.

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Mode of action Chitinases hydrolyze chitin to soluble oligosaccharides, mainly N,N-diacetylchitobiose

(G2), which is further hydrolyzed to G1 (N-acetylglucosamine) by GlcNAcases.

In some study, it is also found that Chitinase gene are also expressed in response to stress

like cold up to -2 to -5ºC.

These Chitinases have significant antifungal activities against plant pathogenic fungi like

Alternaria sp. For grain discoloration of rice, Bipolaris oryzae for brown spot of rice.

The mode of action of PR-3 proteins is relatively simple i.e. Chitinases cleaves the cell

wall chitin polymers in situ, resulting in a weakened cell wall and rendering fungal cells

osmotically sensitive.

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Chitin Binding Protein

All chitin binding proteins do not possess antifungal activities.CBP can be isolate from

plant

1. suger beet,

2. Hortensia

3. tobacco

4. pepper

5. tomato and potato

6. bacteria like Streptomyces tendae.

Moleculer weight of the CBP was found to be in the range of 9 kDa to 30 kDa and having

basic isoelectric pH.

CBP shows strong inhibitory effect against fungi Aspergillus species, Cercospora beticola,

Xanthomonas campestris and many more and several crop fungal pathogen.

Enzymetically CBP has not any function but it binds to insoluble chitin and enhances

hydrolysis of chitin by other enzyme like Chitinase.


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Chitin’s biodegradable and anti-fungal properties are also useful for environmental and

agricultural uses.

Chitooligosaccharides, which are the sugar intermediates released during chitin

hydrolysis, also are pharmaceutically important.

CBP, which binds to the insoluble crystalline substrate, leading to structural changes in

the substrate and increased substrate accessibility.

CBP21 strongly promoted hydrolysis of crystalline chitin by chitinases A and C, while it

was essential for full degradation by chitinase B.

CBP variants with single mutations on the largely polar binding surface lost their ability

to promote chitin degradation, while retaining considerable affinity for the polymer.

Thus, binding alone is not sufficient for CBP21 functionality, which seems to depend on

specific, mostly polar interactions between the protein and crystalline chitin.

Mode of Action

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Thaumatin like protein:-

Occurrence & Properties

Thaumatin-like proteins comprise of polypeptides classes that share homology with

thaumatin, sweet protein from (Bennett) Benth.

Thaumatin-like proteins can be isolated from barley, kiwifruit, maize.

Most of the TLPs have a molecular weight in the range of 18 kDa to 25 kDa and have a pH

in the range from 4.5 to 5.5.

Constitutive levels of Thaumatin-Like Protein is typically absent in healthy plants, with

the proteins being induced exclusively in response to wounding or to pathogen attack

like Uncinula necator, Phomopsis viticola.

Linusitin is a 25-kDa Thaumatin-like Protein isolated from flax seeds.

Linustin shows antifungal activity against Alternaria alternata by the mechanism of

membrane permeabilization. Concentration of protein and lipid and composition of cell

wall of fungi play a major role in these mechanisms.

Pathogenesis Related Protein-5

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Thaumatin production is induced in katemfe fruit in response to an attack upon the

plant by viroid pathogens.

Several members of the thaumatin protein family display significant in vitro inhibition

of hyphal growth and sporulation by various fungi.

The thaumatin protein is considered a prototype for a pathogen-response protein

domain. This thaumatin domain has been found in species as diverse as rice and

Caenorhabditis elegans.

The proteins are involved in systematically acquired resistance and stress response

in plants, although their precise role is unknown.

It is induced by attack by viroids, which are single-stranded unencapsulated RNA

molecules that do not code for protein.

The thaumatin protein I consists of a single polypeptide chain of 207 residues.

Like other PR proteins, thaumatin is predicted to have a mainly beta structure, with a

high content of beta-turns and little helix.

Mode of action

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Pathogenesis Related Protein-6

Plant protease inhibitors:-

The possible role of protease inhibitors (PIs) in plant protection was investigated as

early as 1947 by, Mickel and Standish.

The term “protease” includes both “endopeptidases” and “exopeptidases” whereas,

the term “proteinase” is used to describe only “endopeptidases” (Ryan, 1990).

Several non-homologous families of proteinase inhibitors are recognized among the

animal, microorganisms and plant kingdom.

Majority of proteinase inhibitors studied in plant kingdom originates from three

main families namely leguminosae, solanaceae and gramineae (Richardson, 1991).

Many of protease inhibitors are rich in cysteine and lysine, contributing to better

and enhanced nutritional quality.

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These protease inhibitor genes have practical advantages over genes encoding for

complex pathways i.e. by transferring single defensive gene from one plant species to

another and expressing them from their own wound inducible or constitutive

promoters thereby imparting resistance against insect pests (Boulter, 1993).

Protease inhibitors also exhibit a very broad spectrum of activity including

suppression of pathogenic nematodes like Globodera tabaccum, G. pallida, and

Meloidogyne incognita by CpTi (Williamson and Hussey, 1996).

These inhibitor families that have been found are specific for each of the four

mechanistic classes of proteolytic enzymes, and based on the active amino acid in

their “reaction center” (Koiwa et al. 1997), are classified as serine, cysteine, aspartic

and metallo-proteases.

Mode of action

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Pathogenesis related Protein ( PR-10)

Ribosome inactivating protein

Ribosome-inactivating proteins (RIPs) are toxic N-glycosidases that depurinate the

universally conserved sarcin loop of large rRNAs.

This depurination inactivates the ribosome, thereby blocking its further participation

in protein synthesis.

RIPs are widely distributed among different plant genera and within a variety of

different tissues.

Recent work has shown that enzymatic activity of at least some RIPs is not limited to

site-specific action on the large rRNAs of ribosomes but extends to depurination and

even nucleic acid scission of other targets.

Characterization of the physiological effects of RIPs on mammalian cells has

implicated apoptotic pathways. For plants, RIPs have been linked to defense by

antiviral, antifungal, and insecticidal properties demonstrated in vitro and in

transgenic plants.

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CLASSIFICATION OF RIP

1. Type 1 RIPs, such as pokeweed antiviral protein (PAP), saporin (from soapwort) and

barley translation inhibitor, are monomeric enzymes, each with an approximate MW

of 30,000.

They are basic proteins that share a number of highly conserved active cleft residues

and secondary structure within the active site region but are distinctly different in

overall sequence homology and posttranslational modifications

2. Type 2 RIPs, like ricin and abrin, are highly toxic heterodimeric proteins with

enzymatic and lectin properties in separate polypeptide subunits, each of

approximate MW of 30,000 .

One polypeptide with RIP activity (A-chain) is linked to a galactose binding lectin (B-

chain) through a disulfide bond.

3. Type 3 RIPs, are synthesized as inactive precursors (proRIPs) that require

proteolytic processing events to occur between amino acids involved in formation of

the active site. They are isolated from maize and barley, although several close

relatives of maize, including sorghum.

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Mode of action

Type 1 RIPs from Mirabilis expansa roots were active at microgram levels against

several soil borne bacterial species, the first such demonstration of antibacterial

activity from a plant RIP in bioassays.

In addition, these RIPs were active against a wide variety of both pathogenic and

nonpathogenic fungi including Fusarium and Trichoderma species.

Type 1 barley RIP was inhibitory to fungal growth on solid media when tested against

Trichoderma reesei.

Inhibition of growth in liquid media, however, was minimal with barley RIP alone but

increased dramatically when chitinase was also included.

A type 2 RIP from seeds of the camphor tree Cinnamomum camphora, was toxic to

larvae of mosquito and cotton bollworm.

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Plant defensins:-

Occurance & Properties

The main groups of antimicrobial peptides found in plants are thionins, defensins and lipid transfer proteins. The name “plant defensin” was coined in 1995 by Terras and collegues.

Plant defensins are small (M.W. 5kDa), basic, cysteine-rich antifungal peptides ranging

from 45 to 54 amino acids, and are positively charged.

The first plant defensins were isolated from wheat and barley and were initially classified

as a subgroup of the thionin family called the γ-thionins.

since they showed a similar size and the same number of disulfide bridges as and α β-

thionins.

The plant defensins Rs-AFP1 and Rs-AFP2 from radish, and alfAFP isolated from seeds of

the alfalfa plants, are examples of potent antifungal proteins.


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The structure-activity relationships and modes of action for most of the plant defensins

remain unknown. Not all plant defensins have the same mode of action. Some of them

exhibit potent antifungal activity in vitro at micromolar concentrations against a broad

spectrum of filamentous fungi.

Morphogenic antifungal defensins reduce hyphal elongation and induce hyperbranching,

whereas non-morphogenic defensins reduce hyphal elongation without causing any

morphological distortions.

The antifungal activity of plant defensins, whether morphogenic or not, is reduced by

increasing the ionic strength of the fungal growth assay medium.

Antifungal plant defensin, Rs-AFP2, appears to act primarily at the cell membrane and

induces rapid Ca2+ uptake and K+ efflux from Neurospora crassa hyphae and it may thus

inhibit the growth of filamentous fungi by disrupting cytosolic Ca2+ gradients essential

for hyphal tip growth.

Mode of action

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Example:-

Plant -thionins

Thionins are small, basic plant proteins, 45 to 50 amino acids in length, which include

three or four conserved disulfide linkages.

Thionins are mainly found in seeds where they may act as a defence against consumption

by animals.

A barley leaf thionin that is highly toxic to plant pathogens and is involved in the

mechanism of plant defence against microbial infections has also been identified.

The hydrophobic protein crambin from the Abyssinian kale is also a member of the

thionin family.


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The proteins are toxic to animal cells, presumably attacking the cell membrane and

rendering it permeable, this results in the inhibition of sugar uptake and allows

potassium and phosphate ions, proteins, and nucleotides to leak from cells.

Some thionins are able to inhibit digestive enzymes, bringing thionins to a select

group of plant proteins synthesized in response to insect-pests.

Some thionins described until now are capable to inhibit insect α-amylases and others

could inhibit serine proteases.

γ –hordothionins isolated from sorghum was the first example of a thionin

able to inhibit insect -amylases.

Mode of action

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Example:-LIPID-TRANSFER PROTEINS IN PLANTSProperties:- Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were participate in membrane biogenesis and regulation of the intracellular fatty acid pools. The principle of the assays is to monitor the transfer of labelled lipids from donor to acceptor membranes. Acceptor membranes are either natural membranes such as mitochondria, chloroplasts, plasma membranes, and “microsomes” (endoplasmic rich-fraction) or artificial Membranes (liposomes or lipid vesicles). Donor membranes are either natural membranes or liposomes. The lipids to be transferred are either radioactive, spin labelled, or fluorescent. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions.

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Mode of action

Their mode of action is not completely understood. A shuttle mechanism has been

proposed for the phosphatidylcholine- specific LTP from mammalian cells, which

suggests the formation of a phospholipid-LTP complex that interacts with the

membrane and exchanges its bound phospholipid with a phospholipid molecule from

the membrane. A similar sequence of events has been suggested for plant LTPs.

Such a complex has never been isolated from a plant LTP (and also with nonspecific

LTPs from mammalian cells), which suggests that the binding is too weak to allow

formation of a stable complex.

In contrast, a strong binding of acyl chains or of lyso-phosphatidylcholine has been

noted for several plant LTPs.

These binding properties are in agreement with the model suggesting that LTPs

contain a hydrophobic cavity that can accept one acyl chain but not a whole

phospholipid molecule.

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osmotin

Properties & occurance

Cultured tobacco cells adapted to grow under osmotic stress synthesize and

accumulate a 26 Kda protein (osmotin) which can constitute as much as 12%

of total cellular protein.

In cells adapted to NaCl osmotic occurs in two forms:

1. An aqueous soluble form (osmotin-I) and

2. A detergent soluble form (osmotin II) in the approximate ratio of 2:3.

Osmotin strongly resembles the sweet protein thaumatin in its molecular weight,

amino acid composition, N-terminal sequence, and the presence of a signal peptide

on the precursor protein. Thaumatin does not cross-react with antiosmotin.

Immunocytochemical detection of osmotin revealed that osmotin is concentrated in

dense inclusion bodies within the vacuole. Although antiosmotin did not label

organelles, cell walls, or membranes, osmotin appeared sparsely distributed in the

cytoplasm.

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Mode of action:-

Osmotin and other osmotin-like proteins were shown to have antifungal activity in

vitro against a broad range of fungi, including several plant pathogens.

The fungal growth inhibition by osmotin and zeamatin, a maize PR-5 protein,

correlated with plasma membrane permeabilization and dissipation of the

membrane potential, suggesting a physical interaction between PR-5 proteins and

the plasma membrane of sensitive fungi, but the precise mechanism of cytotoxicity

remains unknown.

Many of the PR proteins, including osmotin, exhibit clear specificity of their toxicity

against fungi, indicating that there must be determinants of sensitivity and resistance

in fungal cells osmotin stimulates a mitogen-activated protein kinase (MAPK) signal

system in yeast to induce changes in the cell wall that enhance cytotoxicity of this

antifungal protein.

It has been suggested earlier that the cytotoxic action of plant antifungal proteins

could involve activation of signaling cascades, based on the ability of G protein

inhibitors to block the cytotoxic effect of plant defensin.

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Other Proteins

Theis et al, 2003 investigated the inhibitory effects of the antifungal protein (AFP)

from Aspergillus giganteus.

AFP is a highly basic (Isoelectric point 8.8) polypeptide of 51 amino acids with a

high content of cysteine, tyrosine, and lysine residues.

Seetharaman et al. (1996) identified other AFPs, sormatin,, that increase during

caryopsis development; they were high at physiological maturity and decrease at

combine harvest maturity of the grain.

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They show that the growth inhibitory effect of the AFP is caused by

permebealization of the fungal membranes by using an assay based on the uptake of

the fluorescent dye SYTOX Green.

Pozo et al., 2002 also found the same AFP protein from the Aspergillus giganteus, it

promotes charge neutralization and condensation of DNA as demonstrated by

electrophoretic mobility shift and ethidium bromide displacement assays.

Hagen et al., 2007 found AFP can inhibit the chitin synthesis by the In situ chitin

synthase activity assays.

It indicate that AFP causes cell wall stress and disturbs cell integrity by inactivating

chitin synthase that results in membrane permeability.

Mode of action

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Function of PR protein:-

1. PRs are synthesized in response to some type of stress, their function analogs to the

one postulated heat shock protein might be protect the plant from extensive

damage.

2. During hypersensitive reaction, PRs are first detectable in a ring around are necrosis

center.

3. In the subsequent phase of slow lesion expansion, they reach the highest

concentration at the lesion margin

4. they also accumulate between lesion in that inoculated leaves & may appear in lower

concentration in distant non infected leaves.

5. the occurrence of PRs merely reflects a particular type of stress which changes the

metabolism of the plant & induces as well as resistance further to infection.

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Conclusion PR proteins play important role in disease resistance, seed germination and also help

the plant to adapt to the environmental stress.

The increasing knowledge about the PR proteins gives better idea regarding the

development and defense system of plants.

Primary aspects of the gene regulation of the PR proteins are understood but the

study of exact mechanism of gene regulation and receptor cascade will open new

ways for the plant genetic engineering technology for crop improvement.

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Recent studies

1. Additional resistance gene(s) against Cladosporium fulvum present on the Cf-9

introgression segment have been shown to be associated with strong PR-protein

accumulation (Laugé et al., 1998).

2. In some pathosystems mRNAs for certain PRs members accumulate to similar levels

in compatible and incompatible interactions, but the maximum level of expression is

reached much faster in the latter (Van Kan et al., 1992).

3. Accumulation of PRs in plants in which resistance is locally or systemically induced.

Generalizing this broad research area it can be stated that PRs are recognized

as markers of the systemic acquired resistance (SAR), and PRs genes are involved

in the list of the so-called SAR-genes (Ward et al., 1991).

4. Some SAR-inducing chemicals, such as benzothiadiazole (BTH), -β aminobutyric acid

(BABA) or 2,6-dichloroisonicotinic acid (DCINA) are harmless commercially

supplied compounds and have promising practical application as novel tools in plant

protection (Van Loon, 1997; Ku, 2001; Edreva, 2004 and references therein).

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5. Gene-engineering of PR-5 is another promising strategy for improvement of crop

disease resistance, based on the potent plasmolyzing and antifungal effect of this PRs

family.

6. Overexpression of a pepper basic pathogenesis related protein 1 gene in tobacco

plants enhances resistance to heavy metal and pathogen stresses (Sarowar et al.,

2005).

7. For biotechnological purposes PR genes are transferred from novel sources, such as

the insectivorous sundew (Drosera rotundifolia L.) (Matušikova et al., 2004).

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Thank You

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Pr protein