Pathogenesis-related proteins (initially named “b” proteins) were discovered in tobacco leaves hypersensitively reacting to TMV by two independently working groups (Van Loon and Van Kammen, 1970; Gianinazzi et al., 1970)

1. Department of Mycology and Plant Pathology
Institute of Agricultural Sciences
Banaras Hindu University
Presented by:
Mamoon Rasheed
M.Sc. (Ag.) Prev

2. • Pathogenesis-related proteins (initially named “b” proteins) were discovered in tobacco leaves
hypersensitively reacting to TMV by two independently working groups (Van Loon and Van Kammen,
1970; Gianinazzi et al., 1970)
• Assumption : These proteins are commonly induced in resistant plants, expressing a hypersensitive
necrotic response (HR) to pathogens of viral, fungal and bacterial origin.
• Later, however, it turned out that b-proteins are induced not only in resistant, but also in susceptible
plant – pathogen interactions, as well as in plants, subjected to abiotic stress factors (Van Loon, 1985)
• 1980 Antoniw et al. coined the term “pathogenesis-related proteins” (PRs), which have been defined
as “proteins encoded by the host plant but induced only in pathological or related situations”, the
latter implying situations of non-pathogenic origin.
Where it all started
Source : Edreva, A. (2005). Pathogenesis-related proteins: research progress in the last 15 years. Gen Appl Plant
Physiol, 31(1-2), 105-24.

3. • Originally, five main groups of PRs (PR-1 to PR-5) - numbered in order of decreasing
electrophoretic mobility. Each group consists of several members with similar properties
(Bol et al., 1990)
• Criteria used for the inclusion of new families into PRs are that
(a)The protein must be induced by a pathogen in tissues that do not normally express it
(b)Induced expression must occur in at least two different plant-pathogen
combinations, or expression in a single plant-pathogen combination must be confirmed
independently in different laboratories (Van Loon and Van Strien, 1999)
Classification
Citation : Edreva, A. (2005). Pathogenesis-related proteins: research progress in the last 15 years. Gen Appl Plant
Physiol, 31(1-2), 105-24.

4. Text
Head
Citation : Van Loon, L. C., & Van Strien, E. A. (1999). The families of pathogenesis-related proteins, their activities, and comparative
analysis of PR-1 type proteins. Physiological and molecular plant pathology, 55(2), 85-97.

5. Head
Citation : van Loon, L. C., Rep, M., & Pieterse, C. M. (2006). Significance of inducible defense-related proteins in infected plants. Annu. Rev.
Phytopathol., 44, 135-162.

6. • They are low-molecular proteins (6-43 kDa), extractable and stable at low pH (< 3),
thermostable, and highly resistant to proteases (Van Loon, 1999).
• Apart from being present in the primary and secondary cell walls of infected plants,
PRs are also found in cell wall appositions (papillae) deposited at the inner side of
cell wall in response to fungal attack (Benhamou et al., 1991; Jeun, 2000).
• PRs are established in all plant organs – leaves, stems, roots, flowers (Van Loon,
1999), being particularly abundant in the leaves, where they can amount to 5-10% of
total leaf proteins.
Biochemical and structural character

7. • The four α-helices I to IV are shown red and yellow, the
four β-strands A to D cyan arranged antiparallel
between helices, other polypeptide segments gray, and
the polypeptide chain ends are indicated with N and C.
• The tight packing of the α-helices on both sides of the
central β-sheet (α−β−α sandwich structure) results in a
compact, bipartite molecular core, which is stabilized
by hydrophobic interactions and multiple hydrogen
bonds
Biochemical and structural character
Citation : Fernández, C., Szyperski, T., Bruyere, T., Ramage, P., Mösinger, E., & Wüthrich, K. (1997). NMR solution
structure of the pathogenesis-related protein P14a. Journal of molecular biology, 266(3), 576-593.
The structure of a PR-1 family member (tomato PR1-b) was
solved by nuclear magnetic resonance

8. • 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
PR2

9. PR2 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.

10. • 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
PR3

11. • 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.
• Bipolaris oryzae for brown spot of rice
PR3 Mode of action
Citation : Nejad, M. S., Bonjar, G. H. S., & Dehkaei, F. P. (2014). Control of Bipolaris oryzae the causal agent of rice
brown spot disease via soil Streptomyces sp. isolate G. International Journal of Advanced Biological and Biomedical
Research, New Delhi, 2, 310-317.

12. • 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
• Serine proteinase inhibitors
• Cysteine proteinase inhibitors
• Aspartate/metallo proteinase inhibitor
PR6

13. • 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
PR6 Mode of action

14. • “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
PR12

15. • 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
PR12 Mode of action

16. PR12 Mode of action
https://www.macmillanhighered.com/BrainHoney/Resource/6716/digital_first_content/trunk/test/hillis2e/hillis2e_ch28_2.html

17. • Recent report shows that SA-dependent expression of PR-1, PR-2, and PR-5 is required for
increased protection against the biotrophic fungus Peronospora parasitica in Arabidopsis,
whereas SA-independent but JA-dependent induction of PR-3 and PR-4 is associated with
the induced resistance against the necrotrophic fungi A. brassicicola (Penninckx et al.
1996)
• SA induces acidic PR genes that are normally activated during SAR, whereas ethylene and
jasmonates are known to induce proteinase inhibitors, defensin, thionin, and basic PR
proteins (Epple et al. 1995; Donnell, et al. 1996; Penninckx et al. 1996)
Role of PR in SAR ISR
Citation : Jain D., Khurana J.P. (2018) Role of Pathogenesis-Related (PR) Proteins in Plant Defense Mechanism. In:
Singh A., Singh I. (eds) Molecular Aspects of Plant-Pathogen Interaction. Springer, Singapore

18. PR pattern in R vs S
Citation : CV, Tonón & Guevara, María & Oliva, Claudia & GR, Daleo. (2002). Isolation of a Potato Acidic 39 kDa
β‐1,3‐glucanase with Antifungal Activity against Phytophthora infestans and Analysis of its Expression in Potato
Cultivars Differing in their Degrees of Field Resistance. Journal of Phytopathology. 150. 189 - 195.
10.1046/j.1439-0434.2002.00729.x.
• beta-1,3-glucanase extracted (GLU-39), The enzyme produces a direct inhibitory effect on the germination
of sporangia of P. infestans.
• In the resistant cultivar (cv Pampeana INTA) GLU-39 induction (four-fold with respect to healthy tubers)
occurred 14 h after inoculation and remained over basal levels at 38 h after inoculation.
• By contrast, in the susceptible cultivar (cv Bintje), GLU-39 was induced at lower levels than those observed
in cv Pampeana INTA, and no differences were detected between wounding and infection.
• Stronger accumulation of PRs in inoculated resistant as compared to susceptible plants
• 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)

19. Relevance of PRs to disease resistance
• Important constitutive expression of PRs in plants with high level of natural disease resistance. This
correlation was observed in several pathosystems, such as apple – Venturia inaequalis (Gau et al.,
2004)
• Significant constitutive expression of PRs in transgenic plants overexpressing PR genes accompanied
by increased resistance to pathogens. Thus, increased tolerance to Peronospora tabacina and
Phytophthora parasitica var. nicotianae was demonstrated in tobacco overexpressing PR1a gene
(Alexander et al., 1993).
• silencing of PR-1b gene in barley facilitates the penetration of the fungal pathogen Blumeria graminis f.
sp. hordei in the leaves (Schultheiss et al., 2003).
• Accumulation of PRs in plants in which resistance is locally or systemically induced

20. Commercial and engineering
• Increased resistance to crown rust disease in transgenic Italian ryegrass expressing the rice chitinase
gene was demonstrated (Takahashi et al., 2005)
• Brassica napus transgenic plants, constitutively expressing a chimeric chitinase gene, display field
tolerance to fungal pathogens (Grison et al., 1996)
• The constitutive overexpression of tobacco class I PR-2 and PR-3 transgenes in potato plants
enhanced their resistance to Phytophthora infestans, the causal agent of late blight (Bachmann et
al., 1998)
• overexpression of the cloned rice thaumatin-like (PR-5) gene in transgenic rice plants enhanced the
environmental friendly resistance to Rhizoctonia solani causing sheath blight disease (Datta et al.,
2001)

21. 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.