Pathogenesis-related (PR) proteins are proteins produced in plants in the event of a pathogen attack.[1] They are induced as part of systemic acquired resistance. Infections activate genes that produce PR proteins. Some of these proteins are antimicrobial, attacking molecules in the cell wall of a bacterium or fungus. Others may function as signals that spread “news” of the infection to nearby cells. Infections also stimulate the cross-linking of molecules in the cell wall and the deposition of lignin, responses that set up a local barricade that slows spread of the pathogen to other parts of the plant

1. UNIVERSITY OF AGRICULTURAL SCIENCES BANGLORE
COLLEGE OF AGRICULTURE V.C. FARM , MANDYA
Course: Disease Resistance in Plants,PAT 515 (1+1)
Topic: P. R. Proteins
SUBMITTED TO
DR. Jadesha
SUBMITTED BY
Reddy Kumar A V
PAMM1026
Msc 1st year
COA, Mandya

2. INTRODUCTION
 PR protein, 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.
 Exist in plant cells both intracellularly and also in the intercellularly.

4. INTRODUCTION
 Different plant organs, e.g., leaves, seeds, and roots, may produce different sets of PR
proteins.
 They are either extremely acidic or extremely basic and therefore are highly soluble and
reactive.
 Seventeen families (Van Loon et al., 2006).
 Inhibit the invading pathogens by their enzymatic activities 
 The signal compounds responsible for induction of PRPs include salicylic acid, ethylene,
xylanase, the polypeptide systemin and jasmonic acid.

6.  Although healthy plants may contain trace amounts of several PRPs, attack by pathogens, treatment with
elicitors, wounding, or stress induce transcription of a battery of genes that code for PRPs.

8. Occurrence and Distribution
 Thirty-three PR proteins - tobacco, 20 - sugar beet and more than 30 - Norway spruce
 Glucanases and chitinases - potato plants
 PR proteins developmentally regulated and are found in leaves of healthy tobacco plants during flowering and
are constitutively present in bean leaves
 In potato, leaving aside the leaves, PR 10a is reported to accumulate in tubers, petioles and stem region after
infection

11. Association of PRPs with Disease Resistance
Pathogen Inducible
 Bacteria, fungi, viruses and nematodes induce PR proteins upon entry into the incompatible host
 Rice leaves inoculated with Pseudomonas syringae enhance the production of PR-1, 2,3,5 and 9
 PR-6 proteins showed increasing accumulating trends in tomato and pepper when inoculated with
Xanthomonas vesicatoria
 peroxidases, glucanases and chitinases are found to increase in rice upon inoculation with Erwinia caratovora

13. Pathogenesis Related Function of PRPs
Possible function of PRPs
 Plays important role in defence not only against pathogen infection but also in eliciting acquired resistance
 Glucanases and the chitinases might be involved in the recognition process-releasing defence activating
signaling molecules from the invading pathogen Antimicrobial Properties of PR Proteins
 PR-1, 2, 3, 4 and 5 - inhibit growth of fungi
 Tobacco gp 35 with glucanase like properties and gp 22 with PR-5 inhibit the viral infection
 PR-1 was inhibited oomycetes like Phytophthora parasitica and Peronospora tabacina and bacteria like
Pseudomonas syringae.

14. PR-1 Protein
 Detected - Rice, Wheat, Barley, Corn, Tomato, Tobacco and several other Plant species belonging to
Graminae, Solanacae , Amaranthaceae And Chenopodiaceae (Rodrigues et al., 2005: Makandar et al., 2006).
 Soluble in acidic buffers (pH 3.0) .
 Molecular weight ranges from 14 to 16 kDa.

15. Mode of action
• Strengthening of host cell walls to prevent spread of the Pathogen (santen et al., 2005)
• Inhibitory function on growth of the pathogen (santen et al., 2005)
• In tomato leaves inhibit germination of zoospores and pathogenicity of Phytophthora
infestance

16. PR-2 Proteins
 Shows β-1,3-glucanase activity
M.W. of β -1,3-Gs 33 to 44 kDa
In Nicotiana species: Class I: PR2e subgroup, these are
basic protein localized in cell vacuole
Class II: PR2a ,PR2b and PR2c subgroup, these are acidic
protein Class III: include - PR2d subgroup it is also acidic
protein but differs in sequence by at least 43% from class I
and class II

17. Mode of action
β-1,3-glucanases are involves in hydrolytic cleavage of the
1,3-β-D-glucosidic linkages in β- 1,3-glucans, a major
componant of fungi cell wall.
So that cell lysis and cell death occur as a result of
hydrolysis of glucans present in the cell wall of fungi.

18. PR-3 Proteins
Shows Chitinase activity
Chitinases are endo β-1,4-glucosaminidases which
hydrolyze the β-glycosidic bond at the reducing end of
lucosaminidinides found in chitin, chitosan or
peptidoglycan (Neuhaus,1999)
Most of Chitinase having molecular mass in the range of
15 kDa and 43 kDa
Chitinase can be isolated from Chickpea, Cucumber, barley.

19. Mode of action
• Cleaves the cell wall chitin polymers , resulting in a weakened cell
wall and rendering fungal cells osmotically sensitive
• 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.

20. PR-4 Proteins (Chitin Binding Protein)
• Isolate from -sugar beet, tobacco, pepper, tomato and
potato
• Molecular weight -9 kDa to 30 kDa

21. Mode of action
Shows strong inhibitory effect against fungi Aspergillus species,
Cercospora beticola, Xanthomonas campestris and many more and
several crop fungal pathogen
Enzymatically CBP has not any function but it binds to insoluble
chitin and enhances hydrolysis of chitin by other enzyme like
Chitinase

22. PR-5 Proteins (Thaumatin like protein)
Resemblances to sweet- tasting protein ,thaumatin, which occurs in
the fruit of West African shrub (Pierpoint et al., 1987)
Isolated from barley, kiwifruit, maize
Molecular weight -18 kDa to 25 kDa and pH 4.5 to 5.5
Linusitin is a 25-kDa Thaumatin-like Protein isolated from flax seeds

23. Mode of action
Involved in systemetically acquired resistance and stress response in
plants
Thaumatin production is induced in katemfe fruit -by viroid pathogens
Display significant in vitro inhibition of hyphal growth and
sporulation by various fungi.

24. PR-6 Proteins (Plant protease inhibitors)
The possible role of protease inhibitors (PIs) in plant protection was
investigated as early as 1947 by, Mickel and Standish.
Highly stable defensive proteins that are developmentally regulated
and induced only in response to insect and pathogen attack The
proteinase inhibitors are classified into 1. Serine proteinase inhibitors
2. Cysteine proteinase inhibitors 3. Aspartate/metallo proteinase
inhibitor

25. Mode of action
Exhibit a very broad spectrum of activity including suppression of
pathogenic nematodes like Globodera tabaccum, G. pallida, and
Meloidogyne incognita (Williamson and Hussey, 1996)
Based on the active amino acid in their “reaction center” (Koiwa et al.
1997), are classified as serine, cysteine, aspartic and metallo-proteases

26. PR-10 Proteins (Ribosome inactivating protein)
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

27. Mode of action
RIPs are active against a wide variety of both pathogenic and non-
pathogenic fungi including Fusarium and Trichoderma species
A type 2 RIP from seeds of the camphor tree Cinnamomum camphora,
was toxic to larvae of mosquito and cotton bollworm.

28. Pathogenesis related protein-12 (Plant defensins)
“Plant defensin” was coined in 1995 by Terras
 Plant defensins are small (M.W. 5kDa), basic, cysteine-rich
antifungal peptides ranging from 45 to 54 amino acids, and are
positively charged
Isolated from wheat and barley and were initially classified as a
subgroup of the thionin family called the γ-thionins

29. Mode of action
In bacteria, permeabilization coincided with the inhibition of RNA,
DNA and protein synthesis and decreased bacterial viability
Antifungal defensins reduce hyphal elongation and induce
hyperbranching

30. Pathogenesis related protein-13 (Thionins)
45 to 50 amino acids in length, which include three or four conserved
disulfide linkages
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

31. Mode of action
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.
γ –hordothionins isolated from sorghum was the first example of a
thionin able to inhibit insect -amylases

32. PR protein -14 (Lipid-transfer Proteins In Plants)
LTP are basic, 9-kDa proteins present in high amounts in higher plants
Located in the cell wall
LTPs: participation in cutin formation, embryogenesis, defense
reactions against phytopathogens, symbiosis, and the adaptation of
plants to various environmental conditions

33. 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.